Legier Rojas | Universidad Central del Caribe School of Medicine (original) (raw)
Papers by Legier Rojas
Research Square (Research Square), Dec 3, 2023
Biochemistry, Oct 1, 2003
PubMed, 1993
New techniques to control the potential in membrane patches are giving in detail important charac... more New techniques to control the potential in membrane patches are giving in detail important characteristics of the pre- and post-synaptic channels. When used to assess the quantal size regulation during synchronous (evoked) or asynchronous (spontaneous) release of neurotransmitter can provide valuable information above this process. The macropatch technique (a version of the original patch clamp technique), has advantages in comparison with other macroscopic voltage clamp techniques to record the miniature end-plate current, mepc. During this focal recording, the puzzle size variation of mepc's amplitudes produced, from events generated over distant parts of the cell, are removed. The quantal response is an important feature during synaptic plasticity. Therefore, in this review we focus on pre- and post-synaptic aspects from the quantal asynchronous release of neurotransmitter, that occurs in the neuromuscular junction. We take emphasis on the caudal muscle of tadpoles from amphibian.
PubMed, 1992
The action of ATP on Ca(2+)-dependent K+ channels was studied in fresh human erythrocytes using p... more The action of ATP on Ca(2+)-dependent K+ channels was studied in fresh human erythrocytes using patch-clamp techniques. Single-channel current was recorded at pH 6.5 from inside-out patches in the presence of symmetrical K+ gluconate solutions, containing both 1 microM free Ca2+ in the bath and 0.5 mM LaCl3 on the pipette side. With no ATP, the electrical activity revealed low-conductance K+ channels (25 pS), which showed inward rectification and an opening kinetics dependent on membrane potential. When ATP (1 mM) and Mg2+ (2 mM) were added together and a depolarizing potential was simultaneously applied, only a high-conductance channel (about 75 pS) was observed. This channel showed no rectifying properties and it was not found if ATP was added in the absence of Mg2+. Channel activity was enhanced by adding fluoride (10 mM) or trifluoperazine (50 microM) whilst it was reduced after incubating with dibutyryl cAMP (50 microM) or alkaline phosphatase (250 U/ml). On the other hand, when fragmented membranes from inside-out vesicles were incubated with gamma-32 P-ATP and 1 microM free Ca2+ under above conditions, only two high-molecular weight polypeptides (235 and 320 kDa) were labelled with 32P. The results suggest that ATP-mediated phosphorylation of Ca(2+)-dependent K+ channels leads to a high-conductance state.
The Journal of Membrane Biology, Nov 1, 2006
Biochemistry, Dec 13, 2003
Annals of Neurology, 2002
Quarterly journal of experimental physiology, Jul 16, 1984
Molecular and Cellular Neuroscience, May 1, 2006
Biochemistry, Jul 15, 2004
Journal of Biological Chemistry, Oct 1, 2004
Journal of Biological Chemistry, Dec 1, 2001
Glia, Jan 15, 1999
The radial glial cells that span the retina, described by Müller in 1851, have a remarkable distr... more The radial glial cells that span the retina, described by Müller in 1851, have a remarkable distribution of ion channels in adult amphibia that mediate extracellular K+ spatial buffering. 94% of the total membrane conductance of these cells resides in inward rectifier K+ channels in the endfoot processes apposed to the vitreous humour. We now report that this regional specialization is found in Müller cells isolated from adult (>120 day old) bullfrogs but to a far less extent in those from 10-20 day old tadpoles (stages 34-36). Using the cell attached configuration of the patch-clamp technique, we found, in agreement with previous studies in salamanders, that the endfoot of adult cells had 19.2+/-2.4 (mean +/- S.E., n = 81) channels/patch, whereas the soma had 1.81+/-0.28 (n = 21) channels/patch. In the tadpole, the respective values were 4.29+/-0.26 (n = 79) for the endfoot and 2.26+/-0.24 (n = 27) for the soma. The slope conductance of the inward rectifier K+ channel in 115 mM K+, 19.2+/-0.25 pS (n = 205), channel kinetics and the resting membrane potential (-69+/-2.7 mV, n = 224) were similar at both the endfoot and soma of both adults and embryos. We conclude that during development, the K+ conductance of the Müller cell endfoot, but not of the soma, increases due to a selective clustering of inwardly rectifying K+ channels in that specific region of the cell membrane. The properties of the channels change little during the transformation from tadpole to adult bullfrog.
Journal of Membrane Biology, 2001
The International Journal of Developmental Biology, 2009
Frontiers in Neurology
A product of the immediate early gene Arc (Activity-regulated cytoskeleton-associated protein or ... more A product of the immediate early gene Arc (Activity-regulated cytoskeleton-associated protein or Arc protein) of retroviral ancestry resides in the genome of all tetrapods for millions of years and is expressed endogenously in neurons. It is a well-known protein, very important for synaptic plasticity and memory consolidation. Activity-dependent Arc expression concentrated in glutamatergic synapses affects the long-time synaptic strength of those excitatory synapses. Because it modulates excitatory-inhibitory balance in a neuronal network, the Arc gene itself was found to be related to the pathogenesis of epilepsy. General Arc knockout rodent models develop a susceptibility to epileptic seizures. Because of activity dependence, synaptic Arc protein synthesis also is affected by seizures. Interestingly, it was found that Arc protein in synapses of active neurons self-assemble in capsids of retrovirus-like particles, which can transfer genetic information between neurons, at least acr...
Abstract. A comparison between the Torpedo and muscle-type acetylcholine receptors (AChRs) reveal... more Abstract. A comparison between the Torpedo and muscle-type acetylcholine receptors (AChRs) reveals differences in several lipid-exposed amino acids, particularly in the polarity of those residues. The goal of this study was to characterize the role of eight lipid-exposed residues in the functional differences between the Torpedo and muscle-type AChRs. To this end, residues aS287, aC412, bY441, cM299, cS460, dM293, dS297 and dN305 in the Torpedo AChR were replaced with those found in the muscletype receptor. Mutant receptor expression was measured in Xenopus oocytes using [ 125 I]-a-bungarotoxin, and AChR ion channel function was evaluated using the two-electrode voltage clamp. Eight mutant combinations resulted in an increase (1.5- to 5.2-fold) in AChR expression. Four mutant combinations produced a significant 46 % decrease in the ACh 50% inhibitory concentration (EC 50), while three mutant combinations resulted in 1.7- to 2-fold increases in ACh EC 50. Finally, seven mutant combin...
Research Square (Research Square), Dec 3, 2023
Biochemistry, Oct 1, 2003
PubMed, 1993
New techniques to control the potential in membrane patches are giving in detail important charac... more New techniques to control the potential in membrane patches are giving in detail important characteristics of the pre- and post-synaptic channels. When used to assess the quantal size regulation during synchronous (evoked) or asynchronous (spontaneous) release of neurotransmitter can provide valuable information above this process. The macropatch technique (a version of the original patch clamp technique), has advantages in comparison with other macroscopic voltage clamp techniques to record the miniature end-plate current, mepc. During this focal recording, the puzzle size variation of mepc's amplitudes produced, from events generated over distant parts of the cell, are removed. The quantal response is an important feature during synaptic plasticity. Therefore, in this review we focus on pre- and post-synaptic aspects from the quantal asynchronous release of neurotransmitter, that occurs in the neuromuscular junction. We take emphasis on the caudal muscle of tadpoles from amphibian.
PubMed, 1992
The action of ATP on Ca(2+)-dependent K+ channels was studied in fresh human erythrocytes using p... more The action of ATP on Ca(2+)-dependent K+ channels was studied in fresh human erythrocytes using patch-clamp techniques. Single-channel current was recorded at pH 6.5 from inside-out patches in the presence of symmetrical K+ gluconate solutions, containing both 1 microM free Ca2+ in the bath and 0.5 mM LaCl3 on the pipette side. With no ATP, the electrical activity revealed low-conductance K+ channels (25 pS), which showed inward rectification and an opening kinetics dependent on membrane potential. When ATP (1 mM) and Mg2+ (2 mM) were added together and a depolarizing potential was simultaneously applied, only a high-conductance channel (about 75 pS) was observed. This channel showed no rectifying properties and it was not found if ATP was added in the absence of Mg2+. Channel activity was enhanced by adding fluoride (10 mM) or trifluoperazine (50 microM) whilst it was reduced after incubating with dibutyryl cAMP (50 microM) or alkaline phosphatase (250 U/ml). On the other hand, when fragmented membranes from inside-out vesicles were incubated with gamma-32 P-ATP and 1 microM free Ca2+ under above conditions, only two high-molecular weight polypeptides (235 and 320 kDa) were labelled with 32P. The results suggest that ATP-mediated phosphorylation of Ca(2+)-dependent K+ channels leads to a high-conductance state.
The Journal of Membrane Biology, Nov 1, 2006
Biochemistry, Dec 13, 2003
Annals of Neurology, 2002
Quarterly journal of experimental physiology, Jul 16, 1984
Molecular and Cellular Neuroscience, May 1, 2006
Biochemistry, Jul 15, 2004
Journal of Biological Chemistry, Oct 1, 2004
Journal of Biological Chemistry, Dec 1, 2001
Glia, Jan 15, 1999
The radial glial cells that span the retina, described by Müller in 1851, have a remarkable distr... more The radial glial cells that span the retina, described by Müller in 1851, have a remarkable distribution of ion channels in adult amphibia that mediate extracellular K+ spatial buffering. 94% of the total membrane conductance of these cells resides in inward rectifier K+ channels in the endfoot processes apposed to the vitreous humour. We now report that this regional specialization is found in Müller cells isolated from adult (>120 day old) bullfrogs but to a far less extent in those from 10-20 day old tadpoles (stages 34-36). Using the cell attached configuration of the patch-clamp technique, we found, in agreement with previous studies in salamanders, that the endfoot of adult cells had 19.2+/-2.4 (mean +/- S.E., n = 81) channels/patch, whereas the soma had 1.81+/-0.28 (n = 21) channels/patch. In the tadpole, the respective values were 4.29+/-0.26 (n = 79) for the endfoot and 2.26+/-0.24 (n = 27) for the soma. The slope conductance of the inward rectifier K+ channel in 115 mM K+, 19.2+/-0.25 pS (n = 205), channel kinetics and the resting membrane potential (-69+/-2.7 mV, n = 224) were similar at both the endfoot and soma of both adults and embryos. We conclude that during development, the K+ conductance of the Müller cell endfoot, but not of the soma, increases due to a selective clustering of inwardly rectifying K+ channels in that specific region of the cell membrane. The properties of the channels change little during the transformation from tadpole to adult bullfrog.
Journal of Membrane Biology, 2001
The International Journal of Developmental Biology, 2009
Frontiers in Neurology
A product of the immediate early gene Arc (Activity-regulated cytoskeleton-associated protein or ... more A product of the immediate early gene Arc (Activity-regulated cytoskeleton-associated protein or Arc protein) of retroviral ancestry resides in the genome of all tetrapods for millions of years and is expressed endogenously in neurons. It is a well-known protein, very important for synaptic plasticity and memory consolidation. Activity-dependent Arc expression concentrated in glutamatergic synapses affects the long-time synaptic strength of those excitatory synapses. Because it modulates excitatory-inhibitory balance in a neuronal network, the Arc gene itself was found to be related to the pathogenesis of epilepsy. General Arc knockout rodent models develop a susceptibility to epileptic seizures. Because of activity dependence, synaptic Arc protein synthesis also is affected by seizures. Interestingly, it was found that Arc protein in synapses of active neurons self-assemble in capsids of retrovirus-like particles, which can transfer genetic information between neurons, at least acr...
Abstract. A comparison between the Torpedo and muscle-type acetylcholine receptors (AChRs) reveal... more Abstract. A comparison between the Torpedo and muscle-type acetylcholine receptors (AChRs) reveals differences in several lipid-exposed amino acids, particularly in the polarity of those residues. The goal of this study was to characterize the role of eight lipid-exposed residues in the functional differences between the Torpedo and muscle-type AChRs. To this end, residues aS287, aC412, bY441, cM299, cS460, dM293, dS297 and dN305 in the Torpedo AChR were replaced with those found in the muscletype receptor. Mutant receptor expression was measured in Xenopus oocytes using [ 125 I]-a-bungarotoxin, and AChR ion channel function was evaluated using the two-electrode voltage clamp. Eight mutant combinations resulted in an increase (1.5- to 5.2-fold) in AChR expression. Four mutant combinations produced a significant 46 % decrease in the ACh 50% inhibitory concentration (EC 50), while three mutant combinations resulted in 1.7- to 2-fold increases in ACh EC 50. Finally, seven mutant combin...