Ricardo Bull | Universidad de Chile (original) (raw)
Papers by Ricardo Bull
International Journal of Molecular Sciences, 2018
Ventricular arrhythmias are a common cause of sudden cardiac death, and their occurrence is highe... more Ventricular arrhythmias are a common cause of sudden cardiac death, and their occurrence is higher in obese subjects. Abnormal gating of ryanodine receptors (RyR2), the calcium release channels of the sarcoplasmic reticulum, can produce ventricular arrhythmias. Since obesity promotes oxidative stress and RyR2 are redox-sensitive channels, we investigated whether the RyR2 activity was altered in obese mice. Mice fed a high fat diet (HFD) became obese after eight weeks and exhibited a significant increase in the occurrence of ventricular arrhythmias. Single RyR2 channels isolated from the hearts of obese mice were more active in planar bilayers than those isolated from the hearts of the control mice. At the molecular level, RyR2 channels from HFD-fed mice had substantially fewer free thiol residues, suggesting that redox modifications were responsible for the higher activity. Apocynin, provided in the drinking water, completely prevented the appearance of ventricular arrhythmias in HFD-fed mice, and normalized the activity and content of the free thiol residues of the protein. HFD increased the expression of NOX4, an isoform of NADPH oxidase, in the heart. Our results suggest that HFD increases the activity of RyR2 channels via a redox-dependent mechanism, favoring the appearance of ventricular arrhythmias.
Frontiers in Ageing Neuroscience, 2018
We have previously reported that primary hippocampal neurons exposed to synaptotoxic amyloid beta... more We have previously reported that primary hippocampal neurons exposed to synaptotoxic amyloid beta oligomers (AbOs), which are likely causative agents of Alzheimer’s disease (AD), exhibit abnormal Ca2+ signals, mitochondrial dysfunction and defective structural plasticity. Additionally, AbOs-exposed neurons exhibit a decrease in the protein content of type-2 ryanodine receptor (RyR2) Ca2+ channels, which exert critical roles in hippocampal synaptic plasticity and spatial memory processes. The antioxidant N-acetylcysteine (NAC) prevents these deleterious effects of AbOs in vitro. The main contribution of the present work is to show that AbOs injections directly into the hippocampus, by engaging oxidation-mediated reversible pathways significantly decreased RyR2 protein content but increased single RyR2 channel activation by Ca2+ and caused considerable spatial memory deficits. AbOs injections into the CA3 hippocampal region impaired rat performance in the Oasis maze spatial memory task, decreased hippocampal glutathione levels and overall content of plasticity-related proteins (c-Fos, Arc, and RyR2) and increased ERK1/2 phosphorylation. In contrast, in hippocampus-derived mitochondria-associated membranes (MAM) AbOs injections increased RyR2 levels. Rats fed with NAC for 3-weeks prior to AbOs injections displayed comparable redox potential, RyR2 and Arc protein contents, similar ERK1/2 phosphorylation and RyR2 single channel activation by Ca2+ as saline-injected (control) rats. NAC-fed rats subsequently injected with AbOs displayed the same behavior in the spatial memory task as control rats. Based on the present in vivo results, we propose that redox-sensitive neuronal RyR2 channels partake in the mechanism underlying AbOs-induced memory disruption in rodents.
Keywords: Ca 2 +-induced Ca 2 + release Redox signaling Single channel Preconditioning Ischemia/r... more Keywords: Ca 2 +-induced Ca 2 + release Redox signaling Single channel Preconditioning Ischemia/reperfusion The response of ryanodine receptor (RyR) channels to cytoplasmic free calcium concentration ([Ca 2+ ]) is redox sensitive. Here, we report the effects of a mild oxidative stress on cardiac RyR (RyR2) channels in Langendorff perfused rat hearts. Single RyR2 channels from control ventricles displayed the same three responses to Ca 2+ reported in other mammalian tissues, characterized by low, moderate, or high maximal activation. A single episode of 5 min of global ischemia, followed by 1 min of reperfusion, enhanced 2.3-fold the activity of NOX2 compared to controls and changed the frequency distribution of the different responses of RyR2 channels to calcium, favoring the more active ones: high activity response increased and low activity response decreased with respect to controls. This change was fully prevented by perfusion with apocynin or VAS 2870 before ischemia and totally reversed by the extension of the reperfusion period to 15 min. In vitro activation of NOX2 in control SR vesicles mimicked the effect of the ischemia/reperfusion episode on the frequencies of emergence of single RyR2 channel responses to [Ca 2+ ] and increased 2.2-fold the rate of calcium release in Ca 2+-loaded SR vesicles. In vitro changes were reversed at the single channel level by DTT and in isolated SR vesicles by glutaredoxin. Our results indicate that in whole hearts a mild oxidative stress enhances the response of cardiac RyR2 channels to calcium via NOX2 activation, probably by S-glutathionylation of RyR2 protein. This change is transitory and fully reversible, suggesting a possible role of redox modification in the physiological response of cardiac RyR2 to cellular calcium influx.
Cranio®-The Journal of Craniomandibular & Sleep Practice, Jan 20, 2017
This study compares the electromyographic (EMG) activity of the muscles from the lips and hyoid b... more This study compares the electromyographic (EMG) activity of the muscles from the lips and hyoid bone in subjects with or without lip competence. Two groups of 20 subjects each, with or without lip competence were studied. EMG activity of the superior orbicularis oris (SOO), inferior orbicularis oris (IOO), suprahyoid (SH) and infrahyoid (IH) muscles was recorded with the subject seated in the upright position during the following tasks: (1) at rest; (2) speaking; (3) swallowing; (4) forced deep breathing; (5) maximal voluntary clenching; and (6) chewing. EMG activity was significantly higher in subjects without competent lips than with competent lips in the SOO and IOO muscles during tasks 3 and 4, SOO during task 2 and IOO during task 6. EMG activity was similar in the SOO and IOO muscles during tasks 1 and 5, SOO during task 6 and IOO during task 2. Activity of the SH and IH muscles was similar in both groups for all tasks. Higher activity in subjects without competent lips implies a higher muscular effort due to the requirement of lip sealing during functional activities. Hyoid muscular activity was not modified by the presence or absence of lip competence.
Acta Odontologica Scandinavica , Apr 20, 2015
This study evaluated the effect of a natural mediotrusive contact on the electromyographic (EMG) ... more This study evaluated the effect of a natural mediotrusive contact on the electromyographic (EMG) activity of the anterior temporalis and sternocleidomastoid muscles during chewing in healthy subjects. The study sample included two groups of 15 subjects each (Group 1: with natural mediotrusive contact; Group 2: without natural mediotrusive contact). Bilateral surface EMG activity was recorded on anterior temporalis and sternocleidomastoid muscles during unilateral chewing of a half cookie and unilateral chewing of a piece of apple. Anterior temporalis and sternocleidomastoid muscle activity was normalized against activity recorded during maximal voluntary clenching in intercuspal position and maximal intentional isometric head-neck rotation to each side, respectively. The partial and total asymmetry indexes were also calculated. Data were analyzed using Mann-Whitney, Wilcoxon and unpaired t-test. EMG activity of anterior temporalis and sternocleidomastoid muscles showed no significant difference between the groups. EMG activity of anterior temporalis was similar between working and non-working sides during chewing in both groups. EMG activity of sternocleidomastoid muscle was higher in the working side than in the non-working side in Group 2 subjects. Asymmetry indexes were not significantly different between groups. The similar EMG pattern and asymmetry indexes observed suggest the predominance of central nervous control over peripheral inputs on anterior temporalis and sternocleidomastoid motor neuron pools.
American Journal of Physiology - Cell Physiology, Jul 1, 2007
Despite their relevance for neuronal Ca(2+)-induced Ca(2+) release (CICR), activation by Ca(2+) o... more Despite their relevance for neuronal Ca(2+)-induced Ca(2+) release (CICR), activation by Ca(2+) of ryanodine receptor (RyR) channels of brain endoplasmic reticulum at the [ATP], [Mg(2+)], and redox conditions present in neurons has not been reported. Here, we studied the effects of varying cis-(cytoplasmic) free ATP concentration ([ATP]), [Mg(2+)], and RyR redox state on the Ca(2+) dependence of endoplasmic reticulum RyR channels from rat brain cortex. At pCa 4.9 and 0.5 mM adenylylimidodiphosphate (AMP-PNP), increasing free [Mg(2+)] up to 1 mM inhibited vesicular [(3)H]ryanodine binding; incubation with thimerosal or dithiothreitol decreased or enhanced Mg(2+) inhibition, respectively. Single RyR channels incorporated into lipid bilayers displayed three different Ca(2+) dependencies, defined by low, moderate, or high maximal fractional open time (P(o)), that depend on RyR redox state, as we have previously reported. In all cases, cis-ATP addition (3 mM) decreased threshold [Ca(2+)] for activation, increased maximal P(o), and shifted channel inhibition to higher [Ca(2+)]. Conversely, at pCa 4.5 and 3 mM ATP, increasing cis-[Mg(2+)] up to 1 mM inhibited low activity channels more than moderate activity channels but barely modified high activity channels. Addition of 0.5 mM free [ATP] plus 0.8 mM free [Mg(2+)] induced a right shift in Ca(2+) dependence for all channels so that [Ca(2+)] <30 microM activated only high activity channels. These results strongly suggest that channel redox state determines RyR activation by Ca(2+) at physiological [ATP] and [Mg(2+)]. If RyR behave similarly in living neurons, cellular redox state should affect RyR-mediated CICR.
Angle Orthodontist, Jul 15, 1991
Integrated electromyographic activity of masseter and anterior temporal muscles was recorded usin... more Integrated electromyographic activity of masseter and anterior temporal muscles was recorded using bipolar surface electrodes in 33 young adults. Subjects were skeletally classified according to ANB angle reading corrected both for maxillary position and rotation of the jaw. Postural activity for both muscles was higher in Class III subjects than in Class I and Class II, whereas in Class I and II subjects activity was similar. During swallowing, masseter muscle activity in Class III subjects was higher than Classes I and II, whereas anterior temporal muscle activity was not different between Classes III and I. During maximal voluntary clenching, activity was not different among classes. High correlations between electromyographic activity and corrected ANB angle as well as with overjet were observed. Skeletal classification used in the present study may have clinical relevance regarding treatment and prognosis, as well as in the assessment of the relationship between muscular activity and craniofacial characteristics.
Journal of Physiology, 1991
1. The modulation by Ca2+ of the activation by inositol 1,4,5‐trisphosphate (IP3) of Ca2+ channel... more 1. The modulation by Ca2+ of the activation by inositol 1,4,5‐trisphosphate (IP3) of Ca2+ channels present in native sarcoplasmic reticulum membranes from frog skeletal muscle was studied after channel incorporation into planar phospholipid bilayers in the presence of Ca2+ or Ba2+ as current carrier species.
2. Channel activity expressed as fractional open time (Po) was low (less than or equal to 0.15) in the presence of varying free Ca2+ concentrations bathing the myoplasmic face of the channel (cis side), and did not increase significantly between 0.01 and 30 microM‐Ca2+
3. Channel activation mediated by IP3 could be elicited from free Ca2+ levels similar to those of resting skeletal muscle (about 0.1 microM) and was found to be strongly regulated by the free Ca2+ concentration present at the myoplasmic moiety of the channel.
4. Channel activation by 10 microM‐IP3 depended on the Ca2+ concentration on the cis side. Po reached a maximum between pCa 7.0 and 6.0, but decreased at higher concentrations of free Ca2+. Thus, Ca2+ exerted a modulatory influence on IP3‐mediated activation in a concentration range where the channel was insensitive to Ca2+.
5. The results indicate that Ca2+ ions act as modulators of IP3 efficacy to open the channel. This could arise from an interaction of Ca2+ with the channel gating mechanism or with the agonist binding site.
CRANIO®-The Journal of Craniomandibular & Sleep Practice, 2017
To compare the effect of breathing type on the activity of respiratory muscles at different body ... more To compare the effect of breathing type on the activity of respiratory muscles at different body positions. Two groups of 20 subjects each, one with upper costal and the other with costodiaphragmatic breathing, were studied. Electromyographic activity of sternocleidomastoid (SCM), diaphragm (DIA), external intercostal (EIC), and latissimus dorsi (LAT) muscles was recorded at standing and lateral decubitus positions during swallowing and maximal voluntary clenching. All muscles showed higher activity during standing in upper costal breathing subjects except the SCM muscle. EIC activity was higher during standing in the costodiaphragmatic breathing group. Subjects with upper costal breathing showed higher DIA activity than subjects with costodiaphragmatic breathing at both body positions and higher SCM activity at lateral decubitus position, whereas, EIC activity was only higher during swallowing. Subjects with upper costal breathing presented higher respiratory effort than subjects with costodiaphragmatic breathing, being most prominent at the lateral decubitus position.
Biological Research, 2000
The effects of redox reagents on the activity of the intracellular calcium release channels (ryan... more The effects of redox reagents on the activity of the intracellular calcium release channels (ryanodine receptors) of skeletal and cardiac muscle, or brain cortex neurons, was examined. In lipid bilayer experiments, oxidizing agents (2,2'-dithiodipyridine or thimerosal) modified the calcium dependence of all single channels studied. After controlled oxidation channels became active at sub microM calcium concentrations and were not inhibited by increasing the calcium concentration to 0.5 mM. Subsequent reduction reversed these effects. Channels purified from amphibian skeletal muscle exhibited the same behavior, indicating that the SH groups responsible for modifying the calcium dependence belong to the channel protein. Parallel experiments that measured calcium release through these channels in sarcoplasmic reticulum vesicles showed that following oxidation, the channels were no longer inhibited by sub mM concentrations of Mg2+. It is proposed that channel redox state controls the high affinity sites responsible for calcium activation as well as the low affinity sites involved in Mg2+ inhibition of channel activity. The possible physiological and pathological implications of these results are discussed.
American journal of physiology - Cell Physiology, 1994
The effect of halothane on calcium channels present in sarcoplasmic reticulum membranes isolated ... more The effect of halothane on calcium channels present in sarcoplasmic reticulum membranes isolated from frog skeletal muscle was studied at the single channel level after fusing the isolated vesicles into planar lipid bilayers. Addition of 91 microM halothane to the cytosolic compartment containing 1 microM free calcium activated the channel by increasing fractional open time from 0.11 to 0.59, without changing the channel conductance. The activation of the channels by halothane was calcium dependent. At resting calcium concentrations in the cytosolic compartment, halothane failed to activate the channel, whereas maximal activation was found at 10 microM calcium. The free energy of halothane binding to the channel decreased from -5.8 kcal/mol at 1 microM calcium to -6.6 kcal/mol at 10 microM calcium. Halothane increased the open time constants and decreased the closed time constants, indicating that it binds to both the open and the closed configurations of the channel.
Febs Letters, 1993
Calcium channels derived from sarcoplasmic reticulum of frog skeletal muscle were fused with plan... more Calcium channels derived from sarcoplasmic reticulum of frog skeletal muscle were fused with planar lipid bilayers. Fractional open times displayed two types of calcium dependence: (i) blockable channels showed a bell‐shaped calcium dependence with an activation constant of 4.5 μM, a Hill coefficient for activation of 1.46 and a blocking constant of 226 μM, and (ii) non‐blockable channels displayed a sigmoidal calcium dependence with an activation constant of 1.1 μM and a Hill coefficient of 1.42; no blocking effect was seen with calcium up to 0.5 mM. These two types of calcium dependence may underlie the coexistence of two different pathways for calcium release in frog skeletal muscle.
We studied the effects of tetracaine on high conductance (90 pS) calcium channels from frog skele... more We studied the effects of tetracaine on high conductance (90 pS) calcium channels from frog skeletal muscle incorporated into POPE:PS:PC (5:3:2) bilayers, with 37 mM Ca or Ba HEPES in the trans compartment, and 225 mM HEPES-Tris in the cis compartment, at pH 7.4. Cis pCa was controlled in the range 7.0 to 5.0. Tetracaine produced a complex effect on channel kinetics. In channels activated by 1 mM cis ATP (pCa 6 or 5), tetracaine further increased fractional open time (Po) from 0.56 to 1 in a concentration-dependent manner (0.25 to 4 mM), with no change in conductance. Mean duration of open events increased, whereas duration of closed events decreased. In channels activated by caffeine (5 or 10 mM) at pCa 7, tetracaine (0.05 to 1 mM) decreased Po from 0.8 to 0.3. These results suggest that a) there are at least two types of high conductance channels with different pharmacological profiles, or b) there is a single population of channels with different responses to tetracaine depending...
Ryanodine receptor (RyR) channels can participate in the amplification of calcium signals, as the... more Ryanodine receptor (RyR) channels can participate in the amplification of calcium signals, as they are activated by μM increases in cytoplasmic free [Ca2+]. The aim of this research was to determine the calcium dependence of brain RyR-channels at near physiological [ATP] and/or [Mg2+] and after exposure to NO donors. Methods: Endoplasmic reticulum vesicles from rat brain cortex were fused with planar bilayers and channel activity was recorded at various cytoplasmic [Ca2+]. Results: In the presence of 3 mM [ATP], RyR-channels were activated at lower [Ca2+], reaching a higher plateau of maximal activity and were inhibited at higher [Ca2+]. The change in Ca2+ dependence induced by ATP can be interpreted as a decrease in K0.5 for calcium activation and an increase in K0.5 for calcium inhibition. Addition of 0.5 mM free [ATP] and 0.8 mM free [Mg2+] to the cytoplasmic compartment shifted the Ca2+ response curve to higher [Ca2+].
Ryanodine receptor (RyR) channels can participate in the amplification and propagation of calcium... more Ryanodine receptor (RyR) channels can participate in the amplification and propagation of calcium signals through the process of calcium induced calcium release (CICR). The aim of this research was to determine the calcium dependence of brain RyR-channels at near physiological [ATP] and/or [Mg2+] and after exposure to NO donors in vitro. For this purpose, endoplasmic reticulum vesicles obtained from rat brain cortex were fused with planar lipid bilayers and single channel activity was recorded at various cytoplasmic [Ca2+]. In the presence of 3 mM free [ATP] in the cytoplasmic compartment, RyR-channels were activated at lower [Ca2+], reaching a higher plateau of maximal activity and were inhibited at higher [Ca2+], than in the absence of ATP. The changes in the response to Ca2+ induced by ATP can be interpreted as a decrease in K0.5 for calcium activation and an increase in K0.5 for calcium inhibition. Mg2+, added to the cytoplasmic compartment, inhibited RyR-channels in the presenc...
American Journal of Physiology - Cell Physiology, 1996
The effect of halothane on calcium release kinetics was studied in triad-enriched sarcoplasmic re... more The effect of halothane on calcium release kinetics was studied in triad-enriched sarcoplasmic reticulum vesicles from frog skeletal muscle. Release from vesicles passively equilibrated with 3 mM 45CaCl2 was measured in the millisecond time range by use of a fast-filtration system. Halothane (400 microM) increased release rate constants at pH 7.1 and 7.4 as a function of extravesicular pCa. In contrast, halothane at pH 6.8 produced the same stimulation of release from pCa 7.0 to 3.0; no release took place in these conditions in the absence of halothane. Halothane shifted the calcium activation curve at pH 7.1, but not at pH 7.4, to the left and increased channel open probability at pH 7.1 in the cis pCa range of 7.0 to 5.0. These results indicate that cytosolic pCa and pH modulate the stimulatory effects of halothane on calcium release. Furthermore, halothane stimulated release in frog skeletal muscle at low pH and resting calcium concentration, indicating that in frog muscle haloth...
American journal of Physiology - Cell Physiology, 1998
Adenosine 5′-cyclic diphosphoribose [cyclic ADP-ribose (cADPR)], a metabolite of NAD+ that promot... more Adenosine 5′-cyclic diphosphoribose [cyclic ADP-ribose (cADPR)], a metabolite of NAD+ that promotes Ca2+ release from sea urchin egg homogenates and microsomal fractions, has been proposed to act as an endogenous agonist of Ca2+ release in sea urchin eggs. We describe experiments showing that a microsomal fraction isolated from Tetrapigus nyger sea urchin eggs displayed Ca2+-selective single channels with conductances of 155.0 ± 8.0 pS in asymmetric Cs+ solutions and 47.5 ± 1.1 pS in asymmetric Ca2+ solutions. These channels were sensitive to stimulation by Ca2+, ATP, and caffeine, but not inositol 1,4,5-trisphosphate, and were inhibited by ruthenium red. The channels were also activated by cADP-ribose in a Ca2+-dependent fashion. Calmodulin and Mg2+, but not heparin, modulated channel activity in the presence of cADP-ribose. We propose that these Ca2+ channels constitute the intracellular Ca2+-induced Ca2+ release pathway that is activated by cADP-ribose in sea urchin eggs.
![Research paper thumbnail of [Ethics code of the Chilean Biological Society]](https://attachments.academia-assets.com/53723330/thumbnails/1.jpg)
](Revista médica de Chile, 1997
The Chilean Biological Society has approved an ethics code for researchers, elaborated by its Eth... more The Chilean Biological Society has approved an ethics code for researchers, elaborated by its Ethic Committee. The text, with 16 articles, undertakes the main ethical problems that researchers must solve, such as institutional, professional or societal ethics, scientific fraud, breaches in collaborative work, relationships between researchers, participation in juries and committees, ethical breaches in scientific publications, scientific responsibility and punishments. This code declares its respect and valorization of all life forms and adheres to international biomedical ethical codes. It declares that all knowledge, created or obtained by researchers is mankind's heritage.
Cranio : the journal of craniomandibular practice, 1991
The effect of anesthetic blocking of the periodontal afferents of the canine teeth was studied in... more The effect of anesthetic blocking of the periodontal afferents of the canine teeth was studied in order to determine its influence on any changes in the jaw elevation activity. Unilateral integrated EMG recordings were made of the masseter and anterior temporal muscles during maximal voluntary clenching in centric occlusion and laterotrusive position with canine contact. After anesthetic blocking of the periodontal afferents of one or both ipsilateral canines, a significant increase was observed of the EMG activity of both jaw elevator muscles studied, in centric occlusion as well as with canine contact. The elevator activity increase was of a greater magnitude when antagonistic canines were anesthetized. These findings thus support the hypothesis that high threshold periodontal receptors exert an inhibitory effect on jaw elevator muscular activity.
International Journal of Molecular Sciences, 2018
Ventricular arrhythmias are a common cause of sudden cardiac death, and their occurrence is highe... more Ventricular arrhythmias are a common cause of sudden cardiac death, and their occurrence is higher in obese subjects. Abnormal gating of ryanodine receptors (RyR2), the calcium release channels of the sarcoplasmic reticulum, can produce ventricular arrhythmias. Since obesity promotes oxidative stress and RyR2 are redox-sensitive channels, we investigated whether the RyR2 activity was altered in obese mice. Mice fed a high fat diet (HFD) became obese after eight weeks and exhibited a significant increase in the occurrence of ventricular arrhythmias. Single RyR2 channels isolated from the hearts of obese mice were more active in planar bilayers than those isolated from the hearts of the control mice. At the molecular level, RyR2 channels from HFD-fed mice had substantially fewer free thiol residues, suggesting that redox modifications were responsible for the higher activity. Apocynin, provided in the drinking water, completely prevented the appearance of ventricular arrhythmias in HFD-fed mice, and normalized the activity and content of the free thiol residues of the protein. HFD increased the expression of NOX4, an isoform of NADPH oxidase, in the heart. Our results suggest that HFD increases the activity of RyR2 channels via a redox-dependent mechanism, favoring the appearance of ventricular arrhythmias.
Frontiers in Ageing Neuroscience, 2018
We have previously reported that primary hippocampal neurons exposed to synaptotoxic amyloid beta... more We have previously reported that primary hippocampal neurons exposed to synaptotoxic amyloid beta oligomers (AbOs), which are likely causative agents of Alzheimer’s disease (AD), exhibit abnormal Ca2+ signals, mitochondrial dysfunction and defective structural plasticity. Additionally, AbOs-exposed neurons exhibit a decrease in the protein content of type-2 ryanodine receptor (RyR2) Ca2+ channels, which exert critical roles in hippocampal synaptic plasticity and spatial memory processes. The antioxidant N-acetylcysteine (NAC) prevents these deleterious effects of AbOs in vitro. The main contribution of the present work is to show that AbOs injections directly into the hippocampus, by engaging oxidation-mediated reversible pathways significantly decreased RyR2 protein content but increased single RyR2 channel activation by Ca2+ and caused considerable spatial memory deficits. AbOs injections into the CA3 hippocampal region impaired rat performance in the Oasis maze spatial memory task, decreased hippocampal glutathione levels and overall content of plasticity-related proteins (c-Fos, Arc, and RyR2) and increased ERK1/2 phosphorylation. In contrast, in hippocampus-derived mitochondria-associated membranes (MAM) AbOs injections increased RyR2 levels. Rats fed with NAC for 3-weeks prior to AbOs injections displayed comparable redox potential, RyR2 and Arc protein contents, similar ERK1/2 phosphorylation and RyR2 single channel activation by Ca2+ as saline-injected (control) rats. NAC-fed rats subsequently injected with AbOs displayed the same behavior in the spatial memory task as control rats. Based on the present in vivo results, we propose that redox-sensitive neuronal RyR2 channels partake in the mechanism underlying AbOs-induced memory disruption in rodents.
Keywords: Ca 2 +-induced Ca 2 + release Redox signaling Single channel Preconditioning Ischemia/r... more Keywords: Ca 2 +-induced Ca 2 + release Redox signaling Single channel Preconditioning Ischemia/reperfusion The response of ryanodine receptor (RyR) channels to cytoplasmic free calcium concentration ([Ca 2+ ]) is redox sensitive. Here, we report the effects of a mild oxidative stress on cardiac RyR (RyR2) channels in Langendorff perfused rat hearts. Single RyR2 channels from control ventricles displayed the same three responses to Ca 2+ reported in other mammalian tissues, characterized by low, moderate, or high maximal activation. A single episode of 5 min of global ischemia, followed by 1 min of reperfusion, enhanced 2.3-fold the activity of NOX2 compared to controls and changed the frequency distribution of the different responses of RyR2 channels to calcium, favoring the more active ones: high activity response increased and low activity response decreased with respect to controls. This change was fully prevented by perfusion with apocynin or VAS 2870 before ischemia and totally reversed by the extension of the reperfusion period to 15 min. In vitro activation of NOX2 in control SR vesicles mimicked the effect of the ischemia/reperfusion episode on the frequencies of emergence of single RyR2 channel responses to [Ca 2+ ] and increased 2.2-fold the rate of calcium release in Ca 2+-loaded SR vesicles. In vitro changes were reversed at the single channel level by DTT and in isolated SR vesicles by glutaredoxin. Our results indicate that in whole hearts a mild oxidative stress enhances the response of cardiac RyR2 channels to calcium via NOX2 activation, probably by S-glutathionylation of RyR2 protein. This change is transitory and fully reversible, suggesting a possible role of redox modification in the physiological response of cardiac RyR2 to cellular calcium influx.
Cranio®-The Journal of Craniomandibular & Sleep Practice, Jan 20, 2017
This study compares the electromyographic (EMG) activity of the muscles from the lips and hyoid b... more This study compares the electromyographic (EMG) activity of the muscles from the lips and hyoid bone in subjects with or without lip competence. Two groups of 20 subjects each, with or without lip competence were studied. EMG activity of the superior orbicularis oris (SOO), inferior orbicularis oris (IOO), suprahyoid (SH) and infrahyoid (IH) muscles was recorded with the subject seated in the upright position during the following tasks: (1) at rest; (2) speaking; (3) swallowing; (4) forced deep breathing; (5) maximal voluntary clenching; and (6) chewing. EMG activity was significantly higher in subjects without competent lips than with competent lips in the SOO and IOO muscles during tasks 3 and 4, SOO during task 2 and IOO during task 6. EMG activity was similar in the SOO and IOO muscles during tasks 1 and 5, SOO during task 6 and IOO during task 2. Activity of the SH and IH muscles was similar in both groups for all tasks. Higher activity in subjects without competent lips implies a higher muscular effort due to the requirement of lip sealing during functional activities. Hyoid muscular activity was not modified by the presence or absence of lip competence.
Acta Odontologica Scandinavica , Apr 20, 2015
This study evaluated the effect of a natural mediotrusive contact on the electromyographic (EMG) ... more This study evaluated the effect of a natural mediotrusive contact on the electromyographic (EMG) activity of the anterior temporalis and sternocleidomastoid muscles during chewing in healthy subjects. The study sample included two groups of 15 subjects each (Group 1: with natural mediotrusive contact; Group 2: without natural mediotrusive contact). Bilateral surface EMG activity was recorded on anterior temporalis and sternocleidomastoid muscles during unilateral chewing of a half cookie and unilateral chewing of a piece of apple. Anterior temporalis and sternocleidomastoid muscle activity was normalized against activity recorded during maximal voluntary clenching in intercuspal position and maximal intentional isometric head-neck rotation to each side, respectively. The partial and total asymmetry indexes were also calculated. Data were analyzed using Mann-Whitney, Wilcoxon and unpaired t-test. EMG activity of anterior temporalis and sternocleidomastoid muscles showed no significant difference between the groups. EMG activity of anterior temporalis was similar between working and non-working sides during chewing in both groups. EMG activity of sternocleidomastoid muscle was higher in the working side than in the non-working side in Group 2 subjects. Asymmetry indexes were not significantly different between groups. The similar EMG pattern and asymmetry indexes observed suggest the predominance of central nervous control over peripheral inputs on anterior temporalis and sternocleidomastoid motor neuron pools.
American Journal of Physiology - Cell Physiology, Jul 1, 2007
Despite their relevance for neuronal Ca(2+)-induced Ca(2+) release (CICR), activation by Ca(2+) o... more Despite their relevance for neuronal Ca(2+)-induced Ca(2+) release (CICR), activation by Ca(2+) of ryanodine receptor (RyR) channels of brain endoplasmic reticulum at the [ATP], [Mg(2+)], and redox conditions present in neurons has not been reported. Here, we studied the effects of varying cis-(cytoplasmic) free ATP concentration ([ATP]), [Mg(2+)], and RyR redox state on the Ca(2+) dependence of endoplasmic reticulum RyR channels from rat brain cortex. At pCa 4.9 and 0.5 mM adenylylimidodiphosphate (AMP-PNP), increasing free [Mg(2+)] up to 1 mM inhibited vesicular [(3)H]ryanodine binding; incubation with thimerosal or dithiothreitol decreased or enhanced Mg(2+) inhibition, respectively. Single RyR channels incorporated into lipid bilayers displayed three different Ca(2+) dependencies, defined by low, moderate, or high maximal fractional open time (P(o)), that depend on RyR redox state, as we have previously reported. In all cases, cis-ATP addition (3 mM) decreased threshold [Ca(2+)] for activation, increased maximal P(o), and shifted channel inhibition to higher [Ca(2+)]. Conversely, at pCa 4.5 and 3 mM ATP, increasing cis-[Mg(2+)] up to 1 mM inhibited low activity channels more than moderate activity channels but barely modified high activity channels. Addition of 0.5 mM free [ATP] plus 0.8 mM free [Mg(2+)] induced a right shift in Ca(2+) dependence for all channels so that [Ca(2+)] <30 microM activated only high activity channels. These results strongly suggest that channel redox state determines RyR activation by Ca(2+) at physiological [ATP] and [Mg(2+)]. If RyR behave similarly in living neurons, cellular redox state should affect RyR-mediated CICR.
Angle Orthodontist, Jul 15, 1991
Integrated electromyographic activity of masseter and anterior temporal muscles was recorded usin... more Integrated electromyographic activity of masseter and anterior temporal muscles was recorded using bipolar surface electrodes in 33 young adults. Subjects were skeletally classified according to ANB angle reading corrected both for maxillary position and rotation of the jaw. Postural activity for both muscles was higher in Class III subjects than in Class I and Class II, whereas in Class I and II subjects activity was similar. During swallowing, masseter muscle activity in Class III subjects was higher than Classes I and II, whereas anterior temporal muscle activity was not different between Classes III and I. During maximal voluntary clenching, activity was not different among classes. High correlations between electromyographic activity and corrected ANB angle as well as with overjet were observed. Skeletal classification used in the present study may have clinical relevance regarding treatment and prognosis, as well as in the assessment of the relationship between muscular activity and craniofacial characteristics.
Journal of Physiology, 1991
1. The modulation by Ca2+ of the activation by inositol 1,4,5‐trisphosphate (IP3) of Ca2+ channel... more 1. The modulation by Ca2+ of the activation by inositol 1,4,5‐trisphosphate (IP3) of Ca2+ channels present in native sarcoplasmic reticulum membranes from frog skeletal muscle was studied after channel incorporation into planar phospholipid bilayers in the presence of Ca2+ or Ba2+ as current carrier species.
2. Channel activity expressed as fractional open time (Po) was low (less than or equal to 0.15) in the presence of varying free Ca2+ concentrations bathing the myoplasmic face of the channel (cis side), and did not increase significantly between 0.01 and 30 microM‐Ca2+
3. Channel activation mediated by IP3 could be elicited from free Ca2+ levels similar to those of resting skeletal muscle (about 0.1 microM) and was found to be strongly regulated by the free Ca2+ concentration present at the myoplasmic moiety of the channel.
4. Channel activation by 10 microM‐IP3 depended on the Ca2+ concentration on the cis side. Po reached a maximum between pCa 7.0 and 6.0, but decreased at higher concentrations of free Ca2+. Thus, Ca2+ exerted a modulatory influence on IP3‐mediated activation in a concentration range where the channel was insensitive to Ca2+.
5. The results indicate that Ca2+ ions act as modulators of IP3 efficacy to open the channel. This could arise from an interaction of Ca2+ with the channel gating mechanism or with the agonist binding site.
CRANIO®-The Journal of Craniomandibular & Sleep Practice, 2017
To compare the effect of breathing type on the activity of respiratory muscles at different body ... more To compare the effect of breathing type on the activity of respiratory muscles at different body positions. Two groups of 20 subjects each, one with upper costal and the other with costodiaphragmatic breathing, were studied. Electromyographic activity of sternocleidomastoid (SCM), diaphragm (DIA), external intercostal (EIC), and latissimus dorsi (LAT) muscles was recorded at standing and lateral decubitus positions during swallowing and maximal voluntary clenching. All muscles showed higher activity during standing in upper costal breathing subjects except the SCM muscle. EIC activity was higher during standing in the costodiaphragmatic breathing group. Subjects with upper costal breathing showed higher DIA activity than subjects with costodiaphragmatic breathing at both body positions and higher SCM activity at lateral decubitus position, whereas, EIC activity was only higher during swallowing. Subjects with upper costal breathing presented higher respiratory effort than subjects with costodiaphragmatic breathing, being most prominent at the lateral decubitus position.
Biological Research, 2000
The effects of redox reagents on the activity of the intracellular calcium release channels (ryan... more The effects of redox reagents on the activity of the intracellular calcium release channels (ryanodine receptors) of skeletal and cardiac muscle, or brain cortex neurons, was examined. In lipid bilayer experiments, oxidizing agents (2,2'-dithiodipyridine or thimerosal) modified the calcium dependence of all single channels studied. After controlled oxidation channels became active at sub microM calcium concentrations and were not inhibited by increasing the calcium concentration to 0.5 mM. Subsequent reduction reversed these effects. Channels purified from amphibian skeletal muscle exhibited the same behavior, indicating that the SH groups responsible for modifying the calcium dependence belong to the channel protein. Parallel experiments that measured calcium release through these channels in sarcoplasmic reticulum vesicles showed that following oxidation, the channels were no longer inhibited by sub mM concentrations of Mg2+. It is proposed that channel redox state controls the high affinity sites responsible for calcium activation as well as the low affinity sites involved in Mg2+ inhibition of channel activity. The possible physiological and pathological implications of these results are discussed.
American journal of physiology - Cell Physiology, 1994
The effect of halothane on calcium channels present in sarcoplasmic reticulum membranes isolated ... more The effect of halothane on calcium channels present in sarcoplasmic reticulum membranes isolated from frog skeletal muscle was studied at the single channel level after fusing the isolated vesicles into planar lipid bilayers. Addition of 91 microM halothane to the cytosolic compartment containing 1 microM free calcium activated the channel by increasing fractional open time from 0.11 to 0.59, without changing the channel conductance. The activation of the channels by halothane was calcium dependent. At resting calcium concentrations in the cytosolic compartment, halothane failed to activate the channel, whereas maximal activation was found at 10 microM calcium. The free energy of halothane binding to the channel decreased from -5.8 kcal/mol at 1 microM calcium to -6.6 kcal/mol at 10 microM calcium. Halothane increased the open time constants and decreased the closed time constants, indicating that it binds to both the open and the closed configurations of the channel.
Febs Letters, 1993
Calcium channels derived from sarcoplasmic reticulum of frog skeletal muscle were fused with plan... more Calcium channels derived from sarcoplasmic reticulum of frog skeletal muscle were fused with planar lipid bilayers. Fractional open times displayed two types of calcium dependence: (i) blockable channels showed a bell‐shaped calcium dependence with an activation constant of 4.5 μM, a Hill coefficient for activation of 1.46 and a blocking constant of 226 μM, and (ii) non‐blockable channels displayed a sigmoidal calcium dependence with an activation constant of 1.1 μM and a Hill coefficient of 1.42; no blocking effect was seen with calcium up to 0.5 mM. These two types of calcium dependence may underlie the coexistence of two different pathways for calcium release in frog skeletal muscle.
We studied the effects of tetracaine on high conductance (90 pS) calcium channels from frog skele... more We studied the effects of tetracaine on high conductance (90 pS) calcium channels from frog skeletal muscle incorporated into POPE:PS:PC (5:3:2) bilayers, with 37 mM Ca or Ba HEPES in the trans compartment, and 225 mM HEPES-Tris in the cis compartment, at pH 7.4. Cis pCa was controlled in the range 7.0 to 5.0. Tetracaine produced a complex effect on channel kinetics. In channels activated by 1 mM cis ATP (pCa 6 or 5), tetracaine further increased fractional open time (Po) from 0.56 to 1 in a concentration-dependent manner (0.25 to 4 mM), with no change in conductance. Mean duration of open events increased, whereas duration of closed events decreased. In channels activated by caffeine (5 or 10 mM) at pCa 7, tetracaine (0.05 to 1 mM) decreased Po from 0.8 to 0.3. These results suggest that a) there are at least two types of high conductance channels with different pharmacological profiles, or b) there is a single population of channels with different responses to tetracaine depending...
Ryanodine receptor (RyR) channels can participate in the amplification of calcium signals, as the... more Ryanodine receptor (RyR) channels can participate in the amplification of calcium signals, as they are activated by μM increases in cytoplasmic free [Ca2+]. The aim of this research was to determine the calcium dependence of brain RyR-channels at near physiological [ATP] and/or [Mg2+] and after exposure to NO donors. Methods: Endoplasmic reticulum vesicles from rat brain cortex were fused with planar bilayers and channel activity was recorded at various cytoplasmic [Ca2+]. Results: In the presence of 3 mM [ATP], RyR-channels were activated at lower [Ca2+], reaching a higher plateau of maximal activity and were inhibited at higher [Ca2+]. The change in Ca2+ dependence induced by ATP can be interpreted as a decrease in K0.5 for calcium activation and an increase in K0.5 for calcium inhibition. Addition of 0.5 mM free [ATP] and 0.8 mM free [Mg2+] to the cytoplasmic compartment shifted the Ca2+ response curve to higher [Ca2+].
Ryanodine receptor (RyR) channels can participate in the amplification and propagation of calcium... more Ryanodine receptor (RyR) channels can participate in the amplification and propagation of calcium signals through the process of calcium induced calcium release (CICR). The aim of this research was to determine the calcium dependence of brain RyR-channels at near physiological [ATP] and/or [Mg2+] and after exposure to NO donors in vitro. For this purpose, endoplasmic reticulum vesicles obtained from rat brain cortex were fused with planar lipid bilayers and single channel activity was recorded at various cytoplasmic [Ca2+]. In the presence of 3 mM free [ATP] in the cytoplasmic compartment, RyR-channels were activated at lower [Ca2+], reaching a higher plateau of maximal activity and were inhibited at higher [Ca2+], than in the absence of ATP. The changes in the response to Ca2+ induced by ATP can be interpreted as a decrease in K0.5 for calcium activation and an increase in K0.5 for calcium inhibition. Mg2+, added to the cytoplasmic compartment, inhibited RyR-channels in the presenc...
American Journal of Physiology - Cell Physiology, 1996
The effect of halothane on calcium release kinetics was studied in triad-enriched sarcoplasmic re... more The effect of halothane on calcium release kinetics was studied in triad-enriched sarcoplasmic reticulum vesicles from frog skeletal muscle. Release from vesicles passively equilibrated with 3 mM 45CaCl2 was measured in the millisecond time range by use of a fast-filtration system. Halothane (400 microM) increased release rate constants at pH 7.1 and 7.4 as a function of extravesicular pCa. In contrast, halothane at pH 6.8 produced the same stimulation of release from pCa 7.0 to 3.0; no release took place in these conditions in the absence of halothane. Halothane shifted the calcium activation curve at pH 7.1, but not at pH 7.4, to the left and increased channel open probability at pH 7.1 in the cis pCa range of 7.0 to 5.0. These results indicate that cytosolic pCa and pH modulate the stimulatory effects of halothane on calcium release. Furthermore, halothane stimulated release in frog skeletal muscle at low pH and resting calcium concentration, indicating that in frog muscle haloth...
American journal of Physiology - Cell Physiology, 1998
Adenosine 5′-cyclic diphosphoribose [cyclic ADP-ribose (cADPR)], a metabolite of NAD+ that promot... more Adenosine 5′-cyclic diphosphoribose [cyclic ADP-ribose (cADPR)], a metabolite of NAD+ that promotes Ca2+ release from sea urchin egg homogenates and microsomal fractions, has been proposed to act as an endogenous agonist of Ca2+ release in sea urchin eggs. We describe experiments showing that a microsomal fraction isolated from Tetrapigus nyger sea urchin eggs displayed Ca2+-selective single channels with conductances of 155.0 ± 8.0 pS in asymmetric Cs+ solutions and 47.5 ± 1.1 pS in asymmetric Ca2+ solutions. These channels were sensitive to stimulation by Ca2+, ATP, and caffeine, but not inositol 1,4,5-trisphosphate, and were inhibited by ruthenium red. The channels were also activated by cADP-ribose in a Ca2+-dependent fashion. Calmodulin and Mg2+, but not heparin, modulated channel activity in the presence of cADP-ribose. We propose that these Ca2+ channels constitute the intracellular Ca2+-induced Ca2+ release pathway that is activated by cADP-ribose in sea urchin eggs.
Revista médica de Chile, 1997
The Chilean Biological Society has approved an ethics code for researchers, elaborated by its Eth... more The Chilean Biological Society has approved an ethics code for researchers, elaborated by its Ethic Committee. The text, with 16 articles, undertakes the main ethical problems that researchers must solve, such as institutional, professional or societal ethics, scientific fraud, breaches in collaborative work, relationships between researchers, participation in juries and committees, ethical breaches in scientific publications, scientific responsibility and punishments. This code declares its respect and valorization of all life forms and adheres to international biomedical ethical codes. It declares that all knowledge, created or obtained by researchers is mankind's heritage.
Cranio : the journal of craniomandibular practice, 1991
The effect of anesthetic blocking of the periodontal afferents of the canine teeth was studied in... more The effect of anesthetic blocking of the periodontal afferents of the canine teeth was studied in order to determine its influence on any changes in the jaw elevation activity. Unilateral integrated EMG recordings were made of the masseter and anterior temporal muscles during maximal voluntary clenching in centric occlusion and laterotrusive position with canine contact. After anesthetic blocking of the periodontal afferents of one or both ipsilateral canines, a significant increase was observed of the EMG activity of both jaw elevator muscles studied, in centric occlusion as well as with canine contact. The elevator activity increase was of a greater magnitude when antagonistic canines were anesthetized. These findings thus support the hypothesis that high threshold periodontal receptors exert an inhibitory effect on jaw elevator muscular activity.