Ângelo Tomé | University of Coimbra (original) (raw)

Papers by Ângelo Tomé

Inorganic Chemistry, 1992

large complex caused DNA precipitation. At low DNA concentrations, a large number of Mn complex m... more large complex caused DNA precipitation. At low DNA concentrations, a large number of Mn complex molecules will be bound to a given molecule of DNA, while, at higher DNA concentrations, the complex molecules are distributed among many DNA molecules. The change in the trend of the shift in E, of Mnll'P(Di~)~ in the presence of different concentrations of DNA, for example, from positive potentials at low DNA concentrations to more negative values at higher DNA concentrations, indicates that the adsorption process dominates the electrochemical response, over the effect of binding to DNA, at the early stages of the titration. This occurs because adsorption and precipitation are present only at low DNA concentrations. Although we were unable to quantify the binding of Mn"'P(Dis), to DNA, the binding site size was estimated to be about 15 bp. This value agrees with the arithmetic addition of the individual binding site sizes of Mn'I'P (s = 3-4 bp)' and Dis (s = 4-6 bp).s-ll

Journal of Neurochemistry, 2011

Neurological diseases account for approximately 30% of the total disease burden in Europe and neu... more Neurological diseases account for approximately 30% of the total disease burden in Europe and neurodegenerative diseases account for a significant proportion of these (Olesen and Leonardi 2003). The neuromodulation system operated by adenosine has received an increasing attention as a potential novel target to manage neurodegenerative conditions, in view of its combined neuronal, glial and vascular effects (reviewed in Fredholm et al. 2005). This is best exemplified by the current development (phase IIb) of adenosine A 2A receptor (A2AR) antagonists as anti-Parkin-

FEBS Letters, 1995

We have investigated the effects of the phorbol ester 12-myristate 13-acetate (PMA) on depolariza... more We have investigated the effects of the phorbol ester 12-myristate 13-acetate (PMA) on depolarization-evoked Ca 2÷ influx and catecholamine secretion in bovine adrenal chromaffin cells. PMA (100 riM) strongly inhibited K+-evoked [Ca2+]i transients and Mn 2÷ quenching of fura-2 fluorescence. In contrast, 4¢~-phorbol 12,13-didecanoate, a phorbol ester inactive on protein kinase C (PKC), had no effect. Maximal PMA-mediated inhibition occurred at 5-10 min incubations and were variable from cell to cell, ranging from 25 to 65% of controls. The [CaZ+L transients evoked by the L-type Ca 2+ channel activator Bay K 8644 were strongly inhibited by 100 nM PMA. PMA (0.1-10/xM) inhibited K÷-evoked adrenaline and noradrenaline release by 23--44%. The data indicate that phorbol ester-mediated activation of PKC inhibits voltage-sensitive Ca 2+ channels in chromaffin cells, leading to a prominent depression of depolarization-evoked catecholamine secretion.

Brain Research, 2001

Nicotine-induced catecholamine (CA) secretion and inward ionic currents were inhibited by the opi... more Nicotine-induced catecholamine (CA) secretion and inward ionic currents were inhibited by the opioid antagonist naloxone in cultured bovine chromaffin cells. Naloxone inhibited nicotine-induced CA secretion, as detected by an on-line real-time electrochemical technique, in a dose-dependent manner (IC 529 mM). In voltage-clamped chromaffin cells, nicotine (10 mM) evoked an average peak inward 50 current of 2146 pA that was inhibited by low concentrations of naloxone (42% at 0.1 mM). The antagonist also inhibited total charge influx associated with nicotinic receptor activation (53% at 0.1 mM). This provides strong evidence that naloxone modulation of nicotine-induced CA secretion does not involve opioid receptors but results from the direct interaction with the nicotinic receptor itself, which might also be the case for other related opioid compounds.

Both cannabinoid CB1 and adenosine A2A receptors (CB1 receptors and A2A receptors) control synapt... more Both cannabinoid CB1 and adenosine A2A receptors (CB1 receptors and A2A receptors) control synaptic transmission at corticostriatal synapses, with great therapeutic importance for neurological and psychiatric disorders. A postsynaptic CB1−A2A receptor interaction has already been elucidated, but the presynaptic A2A receptor-mediated control of presynaptic neuromodulation by CB1 receptors remains to be defined. Because the corticostriatal terminals provide the major input to the basal ganglia, understanding the interactive nature of converging neuromodulation on them will provide us with novel powerful tools to understand the physiology of corticostriatal synaptic transmission and interpret changes associated with pathological conditions.

Frontiers in Neuroscience, 1970

Proceedings of the National Academy of Sciences of the United States of America, Jan 8, 2015

The consumption of caffeine (an adenosine receptor antagonist) correlates inversely with depressi... more The consumption of caffeine (an adenosine receptor antagonist) correlates inversely with depression and memory deterioration, and adenosine A2A receptor (A2AR) antagonists emerge as candidate therapeutic targets because they control aberrant synaptic plasticity and afford neuroprotection. Therefore we tested the ability of A2AR to control the behavioral, electrophysiological, and neurochemical modifications caused by chronic unpredictable stress (CUS), which alters hippocampal circuits, dampens mood and memory performance, and enhances susceptibility to depression. CUS for 3 wk in adult mice induced anxiogenic and helpless-like behavior and decreased memory performance. These behavioral changes were accompanied by synaptic alterations, typified by a decrease in synaptic plasticity and a reduced density of synaptic proteins (synaptosomal-associated protein 25, syntaxin, and vesicular glutamate transporter type 1), together with an increased density of A2AR in glutamatergic terminals ...

Frontiers in Neuroscience, 2015

ATP is released in an activity-dependent manner from different cell types in the brain, fulfillin... more ATP is released in an activity-dependent manner from different cell types in the brain, fulfilling different roles as a neurotransmitter, neuromodulator, in astrocyte-to-neuron communication, propagating astrocytic responses and formatting microglia responses. This involves the activation of different ATP P2 receptors (P2R) as well as adenosine receptors upon extracellular ATP catabolism by ecto-nucleotidases. Notably, brain noxious stimuli trigger a sustained increase of extracellular ATP, which plays a key role as danger signal in the brain. This involves a combined action of extracellular ATP in different cell types, namely increasing the susceptibility of neurons to damage, promoting astrogliosis and recruiting and formatting microglia to mount neuroinflammatory responses. Such actions involve the activation of different receptors, as heralded by neuroprotective effects resulting from blockade mainly of P2X7R, P2Y1R and adenosine A 2A receptors (A 2A R), which hierarchy, cooperation and/or redundancy is still not resolved. These pleiotropic functions of ATP as a danger signal in brain damage prompt a therapeutic interest to multi-target different purinergic receptors to provide maximal opportunities for neuroprotection.

Neurobiology of disease, Jan 16, 2015

Cognitive impairments in Huntington's disease (HD) are attributed to a dysfunction of the cor... more Cognitive impairments in Huntington's disease (HD) are attributed to a dysfunction of the cortico-striatal pathway and significantly affect the quality of life of the patients, but this has not been a therapeutic focus in HD to date. We postulated that adenosine A2A receptors (A2AR), located at pre- and post-synaptic elements of the cortico-striatal pathways, modulate striatal neurotransmission and synaptic plasticity and cognitive behaviors. To critically evaluate the ability of A2AR inactivation to prevent cognitive deficits in early HD, we cross-bred A2AR knockout (KO) mice with two R6/2 transgenic lines of HD (CAG120 and CAG240) to generate two double transgenic R6/2-CAG120-A2AR KO and R6/2-CAG240-A2AR KO mice and their corresponding wild-type (WT) littermates. Genetic inactivation of A2AR prevented working memory deficits induced by R6/2-CAG120 at postnatal week 6 and by R6/2-CAG240 at postnatal month 2 and postnatal month 3, without modifying motor deficits. Similarly the ...

Frontiers in Cellular Neuroscience, 2014

† These authors have contributed equally to this work.

Lab Anim (NY), 2014

Ketamine is frequently used to induce analgesia or anesthesia in laboratory animals, but its effe... more Ketamine is frequently used to induce analgesia or anesthesia in laboratory animals, but its effects on learning and memory are poorly characterized. Long-term potentiation (LTP) is considered a cellular mechanism for learning and memory. Ketamine administration immediately abolishes hippocampal LTP in vivo, but whether this effect persists is not known. The authors administered one of two doses of ketamine to adult male C57BL/6 mice and measured LTP in hippocampal slices from the mice 24 h later. Neither LTP induction nor LTP maintenance differed significantly in mice that were administered ketamine compared with mice that were administered saline. The findings suggest that a single intraperitoneal dose of ketamine does not persistently alter LTP in adult male mice.

Abbreviations: ACh, acetylcholine; AMPA, α-amino-3-hydroxy-5-methyl-4isoxazolone propionate; DA, ... more Abbreviations: ACh, acetylcholine; AMPA, α-amino-3-hydroxy-5-methyl-4isoxazolone propionate; DA, dopamine; DAT, dopamine transporter; ECL, enhanced chemiluminescence; NAc, nucleus accumbens; nAChRs, nicotinic acetylcholine receptors; NMDA, N-methyl-D-aspartic acid; NSSP, non-synaptic synaptosomal protein; PBS, phosphate-buffered saline, BSA, bovine serum albumin; Post, postsynaptic component of the synaptic active zone; Pre, presynaptic component of the synaptic active zone; Stx-1A, syntaxin-1A; Syn, synaptosomes; t-TBS, Tween-containing Tris-buffered saline; 5IA85380, 5-iodo-A-85380; FURA-2AM, Fura-2-acetoxymethyl ester; DHβE, dihydro-β-erythroidine.

International Journal of Biochemistry and Cell Biology, 2000

Using clonal insulin-secreting BRIN-BD11 cells, we have assessed whether the graded response of t... more Using clonal insulin-secreting BRIN-BD11 cells, we have assessed whether the graded response of the whole cell population to glucose can be accounted for by a dose-dependent recruitment of individual cells, an ampli®cation of the response of the recruited cells or both. Cytosolic free Ca 2+ concentration ([Ca 2+ ] i ) is an established index of bcell function. We used fura-2 micro¯uorescence techniques to assess the [Ca 2+ ] i responsiveness of single BRIN-BD11 cells to glucose and other secretagogues. Glucose (1±16.7 mM) evoked oscillatory [Ca 2+ ] i rises in these cells resembling those found in parental rat pancreatic b-cells. The percentage of glucose-responsive cells was 11% at 1 mM and increased to 40±70% at 3±16.7 mM glucose, as assessed by a single-stimulation protocol. This pro®le was unrelated to possible dierences in the cell cycle, as inferred from experiments where the cultured cells were synchronized by a double thymidine block protocol. Individual cells exhibited variable sensitivities to glucose (threshold range: 1±5 mM) and a variable dose-dependent ampli®cation of the [Ca 2+ ] i responses (EC 50 range: 2± 10 mM), as assessed by a multiple-stimulation protocol. Glyceraldehyde and a-ketoisocaproic acid had glucose-like eects on [Ca 2+ ] i . The data support a mixed model for the activation of insulin-secreting cells. Speci®cally, the graded secretory response of the whole cell population is likely to re¯ect both a recruitment of individual cells with dierent sensitivities to glucose and a dose-dependent ampli®cation of the response of the recruited cells. 7 (L.M. RosaÂ rio).

PLoS ONE, 2014

There is considerable evidence showing that the neurodegenerative processes that lead to sporadic... more There is considerable evidence showing that the neurodegenerative processes that lead to sporadic Parkinson's disease (PD) begin many years before the appearance of the characteristic motor symptoms. Neuropsychiatric, sensorial and cognitive deficits are recognized as early non-motor manifestations of PD, and are not attenuated by the current anti-parkinsonian therapy. Although loss-of-function mutations in the parkin gene cause early-onset familial PD, Parkin-deficient mice do not display spontaneous degeneration of the nigrostriatal pathway or enhanced vulnerability to dopaminergic neurotoxins such as 6-OHDA and MPTP. Here, we employed adult homozygous C57BL/6 mice with parkin gene deletion on exon 3 (parkin 2/2 ) to further investigate the relevance of Parkin in the regulation of nonmotor features, namely olfactory, emotional, cognitive and hippocampal synaptic plasticity. Parkin 2/2 mice displayed normal performance on behavioral tests evaluating olfaction (olfactory discrimination), anxiety (elevated plus-maze), depressive-like behavior (forced swimming and tail suspension) and motor function (rotarod, grasping strength and pole). However, parkin 2/2 mice displayed a poor performance in the open field habituation, object location and modified Y-maze tasks suggestive of procedural and short-term spatial memory deficits. These behavioral impairments were accompanied by impaired hippocampal long-term potentiation (LTP). These findings indicate that the genetic deletion of parkin causes deficiencies in hippocampal synaptic plasticity, resulting in memory deficits with no major olfactory, emotional or motor impairments. Therefore, parkin 2/2 mice OPEN ACCESS

Pfl�gers Archiv European Journal of Physiology, 1994

ATP and adenosine(5')tetraphospho(5')adenosine (Ap4A), released from adrenal chromaffin cells, ar... more ATP and adenosine(5')tetraphospho(5')adenosine (Ap4A), released from adrenal chromaffin cells, are potent stimulators of endothelial cell function. Using single-cell fura-2 fluorescence recording techniques to measure free cytosolic Ca a § concentration ([Caa § we have investigated the role of purinoceptor subtypes in the activation of coculmred chromaffin and endothelial cells. ATP evoked concentration-dependent [Caa § rises (ECso = 3.8 gM) in a subpopulation of chromaffin cells. Both ATP-sensitive and -insensitive cells were potently activated by nicotine, bradykinin and muscarine. Reducing extracellular free Ca a+ concentration to around 100 nM suppressed the [Caa § transient evoked by ATP but not the [Caa+]i response to bradykinin. ATP-sensitive chromaffin cells were also potently stimulated by 2methylthioadenosine triphosphate (2MeSATP; ECso = 12.5 gM) and UTP, but did not respond to either adenosine 5'-[fi-thio]diphosphate (ADP[flS]), a PaY receptor agonist, adenosine 5'-[a,fl-methylene]triphosphate (pp-[CH2]pA), a Pax agonist or AMP. Adrenal endothelial cells displayed concentration-dependent [Caa+]i responses when stimulated with ATP (ECso = 0.86 gM), UTP (ECso = 1.6 gM) and 2MeSATP (ECso = 0.38 gM). 2MeSATP behaved as a partial agonist. Ap~A and ADP[flS] also raised the [Caa+]i in endothelial cells, whereas AMP and pp[CHa]pA were ineffective. Lowering extracellular free Ca a+ to around 100 nM did not affect the peak ATP-evoked [Caa § rise in these cells. It is concluded that different purinoceptor subtypes are heterogeneously distributed among the major cell types of the adrenal medulla. An intracellular Caa+-releasing Pau-type purinoceptor is specifically localized to adrenal endothelial cells, while a subpopulation of chromaffin cells expresses a non-Pax, non-Pay subtype exclusively coupled to Ca 2+ influx.

European Journal of Cell Biology, 2000

We used botulinum neurotoxins (BoNT) to examine whether differences in the secretory activity of ... more We used botulinum neurotoxins (BoNT) to examine whether differences in the secretory activity of noradrenergic and adrenergic chromaffin cells are related to differences in the exocytotic machinery of these two types of bovine adrenal medulla cells. Cleavage of syntaxin and SNAP-25 by BoNT/C1 decreased in a dose-dependent way the release of both noradrenaline and adrenaline, but noradrenaline release was more sensitive to BoNT/C1. Cleavage of SNAP-25 by BoNT/A also had a larger inhibitory effect on noradrenaline release than on adrenaline release. Neither BoNT/C1 nor BoNT/A affected the intracellular Ca2+ responses induced by K+-depolarisation, and the extent of the inhibition of K+-evoked catecholamine release by selective blockers of voltage-gated Ca2+ channels was not affected by BoNT/C1. Therefore, our data do not support the hypothesis of a regulatory effect of syntaxin or SNAP-25 on the activity of Ca2+ channels. The lower sensitivity of adrenaline release to BoNT was not due to a reduced ability of the toxins to enter or to cleave their protein targets in adrenergic cells, since immunoblot analysis showed the cleavage of a larger fraction of syntaxin 1A in adrenergic cells, as compared to the cleavage in noradrenergic cells. The immunoblot analysis also showed larger amounts of syntaxin 1A in noradrenergic chromaffin cells than in adrenergic cells. Thus, in spite of a greater cleavage of syntaxin 1A in adrenergic cells by BoNT/C1, adrenaline release was less sensitive to BoNT/C1, suggesting that the release process in noradrenergic cells might be more dependent on syntaxin 1A and SNAP-25, as compared to adrenergic cells.

Endocrine Journal, 2008

The glucose sensitivity of bursting electrical activity and pulsatile insulin release from pancre... more The glucose sensitivity of bursting electrical activity and pulsatile insulin release from pancreatic islets was determined in absence of functional K ATP channels. Membrane potential, [Ca 2+ ] i and 5-HT/insulin release were measured by intracellular recording, fura-2 fluorescence and 5-HT amperometry, respectively. Single mouse islets, bathed in tolbutamide or glibenclamide and high extracellular Ca 2+ (Ca 2+ o ), displayed bursting activity and concomitant fast [Ca 2+ ] i and 5-HT/insulin oscillations. Sulphonylurea block of K ATP channel current was unaffected by raising Ca 2+ o . Raising glucose or α-ketoisocaproic acid (KIC) concentration from 3 to 30 mM increased spiking activity and burst plateau duration. Staurosporine did not impair glucose potentiation of electrical activity, ruling out the involvement of serine/ threonine kinases. Glucose enhanced both [Ca 2+ ] i and 5-HT/insulin oscillatory activity, causing a ~3-fold increase in overall 5-HT release rate. Cells lacking bursting activity in high Ca 2+ o and low glucose (or KIC) developed a pattern of intensified spiking in response to 11 mM glucose. It is concluded that β-cells exhibit graded oscillatory electrical and secretory responses to glucose in absence of functional K ATP channels. This suggests that, under physiological conditions, early glucose sensing may involve other channels besides the K ATP channel.

Dental Materials, 1996

Objectives. This study evaluated the effects of six phosphoric acidetching agents on dentin, the ... more Objectives. This study evaluated the effects of six phosphoric acidetching agents on dentin, the independent variables being two acid concentrations (10% and 32%-37%) and three thickener conditions (no thickener, silica, and polymer). The tested hypothesis was that the use of different etchants with similar concentrations of phosphoric acid would result in similar depths of dentin demineralization. Methods. Thirty dentin disks were obtained from extracted human teeth by microtome sectioning. The dentin surfaces were etched with one of the etching agents, fixed, dehydrated and dried. The specimens were observed using a FE-SEM. The mean deepest demineralization of intertubular dentin was measured from the fracture surfaces of the disks. These values were analyzed by ANOVA and Duncan's test. The morphological appearance of the dentin surfaces was compared using the following observation criteria: 1) Presence of a cuff of peritubular dentin; 2) Relative thickness of the layer containing residual collagen or smear layer particles; and 3) Formation of a submicron hiatus at the bottom of the exposed collagen network. The pH of each of the etching agents was measured. A correlation analysis was made of the pH vs. the depth of dentin demineralization. Results. Silica-thickened etchants did not demineralize dentin as deeply as did polymer-thickened etchants and unthickened etchants. High magnifications revealed three distinct zones within the demineralized dentin layer: an upper porous zone of residual smear layer or denatured collagen and residual silica particles (in groups etched with silicathickened etchants), an intermediate area with randomly oriented collagen fibers, and a lower zone with a submicron hiatus, few collagen fibers, and scattered hydroxyapatite inclusions. This hiatus was observable in all the specimens etched with the polymer-thickened etchants, in 90% of the specimens etched with the unthickened phosphoric acid liquids, and in 60% of the specimens etched with the silica-thickened gels. Significance. The results obtained suggest that similar concentrations of phosphoric acid etchants containing distinct thickeners result in different demineralization depths as well as different morphology of etched dentin.

Brain Research, 2014

Ketamine Synaptic plasticity Synaptic transmission a b s t r a c t Ketamine, an analgesic/anesthe... more Ketamine Synaptic plasticity Synaptic transmission a b s t r a c t Ketamine, an analgesic/anesthetic drug, is increasingly popular in clinical practice due to its analgesic properties and importance for emergency procedures. The impact of ketamine on basal excitatory synaptic transmission and synaptic plasticity are not yet fully understood. Therefore we investigated the effects of different concentrations of ketamine on basal excitatory synaptic transmission and on two forms of synaptic plasticity: pairedpulse facilitation (PPF) and long-term potentiation (LTP). Evoked field excitatory postsynaptic potentials (fEPSP) were recorded in Schaffer fiber -CA1 pyramid synapses of mouse hippocampal slices and the initial slope of the fEPSP was measured to estimate the percentage of inhibition of the basal synaptic transmission. Presynaptic volley amplitude, PPF and LTP induction and maintenance were also calculated. For basal synaptic transmission and PPF increasing concentrations of ketamine (1, 3, 10, 30, 100, 200, 300 and 600 μM) were applied to each slice and for LTP individual slices were used for each concentration (3, 10, 30 or 100 μM). Clinically relevant concentrations of ketamine decreased LTP in a concentration-dependent manner without changing PPF, whereas basal excitatory synaptic transmission and presynaptic volley amplitude was affected only with high concentrations of ketamine (300 and 600 μM). These results allow dissociating http://dx.(P.O. Ribeiro).

BMC Neuroscience, 2007

Background: 2-Methylthioadenosine 5'-triphosphate (2-MeSATP), formerly regarded as a specific P2Y... more Background: 2-Methylthioadenosine 5'-triphosphate (2-MeSATP), formerly regarded as a specific P2Y (metabotropic) purinergic receptor agonist, stimulates Ca 2+ influx and evokes catecholamine release from adrenal chromaffin cells. These cells express P2Y and P2X (ionotropic) purinoceptors, with the latter providing an important Ca 2+ influx pathway. Using single cell calcium imaging techniques, we have determined whether 2-MeSATP might be a specific P2X receptor agonist in bovine chromaffin cells and assessed the relative role of P2X and P2Y receptors on catecholamine secretion from these cells.