Antonio Carlos Cassola - Academia.edu (original) (raw)
Uploads
Papers by Antonio Carlos Cassola
Clinical Science, 1991
1. The kinetics of acidification of luminal fluid in hypertrophied proximal tubules after unilate... more 1. The kinetics of acidification of luminal fluid in hypertrophied proximal tubules after unilateral nephrectomy was studied by stationary microperfusion and continuous measurement of luminal pH with antimony microelectrodes. 2. Trans-epithelial and basolateral membrane electrical potential differences were measured in order to detect modifications in electrogenic transport mechanisms under these conditions. 3. The values of stationary pH and HCO−3 concentration were significantly lower, the mean acidification half-time was not different and net reabsorptive HCO−3 fluxes in proximal tubules were significantly increased in uninephrectomized rats. According to an electrical analogue model, these results suggest (a) a reduction in the internal series resistance of the H+ pump, caused perhaps by an increased density of pump sites, and (b) an increase in the protonmotive force of the pump. 4. The trans-epithelial electrical potential difference measured in free flow conditions was signif...
Biophysical Journal, 2016
Exchangers within the APC superfamily of transporters. Initial homology models were produced from... more Exchangers within the APC superfamily of transporters. Initial homology models were produced from 10 alternative alignments of these distantly related proteins. The alignments were refined by mapping sequence conservation onto these 3D structures. The best model was then fitted to the cryo-EM map by adjusting the position of individual helices and the resulting structure was equilibrated in a lipid bilayer for 200 ns using molecular dynamics. The resulting structure suggests conformational changes relative to UraA in which helices at the dimer interface are tilted relative to the transporter domain, thus providing access to the substrate binding site from the extracellular side of the membrane. Comparison of our Bor1p structure with that from UraA are likely to reflect the structural changes that accompany the alternating access mechanism employed by this family of transporters.
Pfl�gers Archiv European Journal of Physiology, 1998
A peptide with neurotoxic effect on mammals, purified from the venom of the spider Phoneutria nig... more A peptide with neurotoxic effect on mammals, purified from the venom of the spider Phoneutria nigriventer, was studied regarding its primary structure and its effects on voltage-gated calcium channels. The peptide, named ω-phonetoxin-IIA, has 76 amino acids residues, with 14 Cys forming 7 disulphide bonds, and a molecular weight of 8362.7 Da. The neurotoxicity is a consequence of the peptide’s blocking effects on high-voltage-activated (HVA) calcium channels. N-type HVA calcium channels of rat dorsal root ganglion neurons are blocked with affinity in the sub-nanomolar concentration range. The toxin also blocks L-type channels of rat β pancreatic cells, with an affinity 40 times lower. Although not studied in detail, evidence indicates that the toxin also blocks other types of HVA calcium channels, such as P and Q. No effect was observed on low-voltage-activated, T-type calcium channels. The significant homologies between ω-phonetoxin-IIA and the peptides of the ω-agatoxin-III family, and the overlapping inhibitory effects on calcium channels are discussed in terms of the structure-activity relationship.
Pfl�gers Archiv European Journal of Physiology, 1984
The membrane potential response of proximal tubular cells to changing HCO3 concentrations was mea... more The membrane potential response of proximal tubular cells to changing HCO3 concentrations was measured in micro-puncture experiments on rat kidney in vivo. No significant effect was noticed when luminal bicarbonate concentration was changed. Changing peritubular HCOg by substitution with C1-resulted in conspicuous membrane potential transients, which reached peak values after I00-200 ms and decayed towards near control with time constants of ~ 2 s. The polarity of the potential changes and the dependence of the initial potential deflections on the logarithm of HCO3 concentration suggest a high conductance of the peritubular cell membrane for HCO3 buffer, but not for CI-, SO 2-, or isethionate. At constant pH, tricot was estimated to amount to ~0.68. At constant Pco2, tHco; was even greater because of an additional effect of OH-or respectively H + gradients across the cell membrane. The secondary repolarization may be explained by passive net movements of K § and HCO~ across the peritubular cell membrane, which result in a readjustment of intracellular HCO3 to the altered peritubular HCO3 concentration. Application of carbonic anhydrase inhibitors in the tubular lumen reduced the initial potential response by one half and doubled the repolarization time constant. The same effect occurred instantaneously when the inhibitor was applied together with the HCO3 concentration step-in the peritubular perfusate. This observation demonstrates that membrane bound carbonic anhydrase is somehow involved in passive rheogenic bicarbonate transfer across the peritubular cell membrane, and suggests that HCO; permeation might occur in form of CO2 and OH-(or H § in opposite direction).
Biophysical Journal, 2009
The composition of ionic channels involved in electrogenesis of smooth muscle cells in arterioles... more The composition of ionic channels involved in electrogenesis of smooth muscle cells in arterioles of skeletal muscle is poorly understood. Here, we investigated inward currents responsible for the depolarizing phase of action potential. Although these currents are thought to be primarily through L-type Ca 2þ channels, action potentials recorded in our experiments with perforated patch technique were not eliminated by removal of extracellular Ca 2þ or by addition of L-type Ca 2þ channel blocker nifedipine (10 mM). Na þ channel blocker tetrodotoxin (TTX, 1 mM) abolished action potentials at low (~10 mM), but not normal (2 mM), extracellular Ca 2þ. When recorded with 140 mM Cs þ and 10 mM EGTA in the pipette and 145 mM Na þ and 2 mM Ca 2þ in the bath, the maximal whole-cell currents (at þ10 mM) were 2252 A/F, n¼6. The magnitude of slowly activating/inactivating currents that remained in the presence of 1 mM TTX was 451 A/F. Na þ currents recorded with 10 mM Ca 2þ in the bath were at least twofold smaller than those with~10 mM Ca 2þ. Na þ currents recorded through perforated patch at 2 mM Ca 2þ were reduced in the presence of 10 mM caffeine from 1953 to 954 A/F, n¼4. Our results suggest that TTX-sensitive voltage-gated Na þ channels contribute to depolarization of smooth muscle cells in skeletal muscle arterioles. Voltagegated Na þ channels appear to be under a tight control by intracellular Ca 2þ signaling.
Aplysia brasiliana is a n osmoconforming mollusc; the osmolality of its extracellular fluid follo... more Aplysia brasiliana is a n osmoconforming mollusc; the osmolality of its extracellular fluid follows that of the external media. This investigation analyzes the volume changes of isolated neuron bodies exposed to hypotonic shocks. The abdominal ganglion was isolated, and the volumes of neuron bodies as well as intracellular K' concentration were measured. Hypotonic shocks induce a rapid swelling followed by a slower restoration of cell volume. The regulatory volume decrease (RVD) restores cell volume to its control value. Ba2+ slows RVD without blocking it. Furosemide (in the pM range) completely and reversibly blocks the regulatory volume decrease. On return t o isotonic solution after RVD, cell shrinkage was only detected when furosemide was present. I t is concluded that neuron bodies of A. brasiliana display efficient processes for volume regulation, based on a conductive pathway and a furosemide-sensitive transport mechanism, which is probably the Na-2C1-K cotransporter. A model simulation provides additional support to this hypothesis.
Clinical Science, 1991
1. The kinetics of acidification of luminal fluid in hypertrophied proximal tubules after unilate... more 1. The kinetics of acidification of luminal fluid in hypertrophied proximal tubules after unilateral nephrectomy was studied by stationary microperfusion and continuous measurement of luminal pH with antimony microelectrodes. 2. Trans-epithelial and basolateral membrane electrical potential differences were measured in order to detect modifications in electrogenic transport mechanisms under these conditions. 3. The values of stationary pH and HCO−3 concentration were significantly lower, the mean acidification half-time was not different and net reabsorptive HCO−3 fluxes in proximal tubules were significantly increased in uninephrectomized rats. According to an electrical analogue model, these results suggest (a) a reduction in the internal series resistance of the H+ pump, caused perhaps by an increased density of pump sites, and (b) an increase in the protonmotive force of the pump. 4. The trans-epithelial electrical potential difference measured in free flow conditions was signif...
Biophysical Journal, 2016
Exchangers within the APC superfamily of transporters. Initial homology models were produced from... more Exchangers within the APC superfamily of transporters. Initial homology models were produced from 10 alternative alignments of these distantly related proteins. The alignments were refined by mapping sequence conservation onto these 3D structures. The best model was then fitted to the cryo-EM map by adjusting the position of individual helices and the resulting structure was equilibrated in a lipid bilayer for 200 ns using molecular dynamics. The resulting structure suggests conformational changes relative to UraA in which helices at the dimer interface are tilted relative to the transporter domain, thus providing access to the substrate binding site from the extracellular side of the membrane. Comparison of our Bor1p structure with that from UraA are likely to reflect the structural changes that accompany the alternating access mechanism employed by this family of transporters.
Pfl�gers Archiv European Journal of Physiology, 1998
A peptide with neurotoxic effect on mammals, purified from the venom of the spider Phoneutria nig... more A peptide with neurotoxic effect on mammals, purified from the venom of the spider Phoneutria nigriventer, was studied regarding its primary structure and its effects on voltage-gated calcium channels. The peptide, named ω-phonetoxin-IIA, has 76 amino acids residues, with 14 Cys forming 7 disulphide bonds, and a molecular weight of 8362.7 Da. The neurotoxicity is a consequence of the peptide’s blocking effects on high-voltage-activated (HVA) calcium channels. N-type HVA calcium channels of rat dorsal root ganglion neurons are blocked with affinity in the sub-nanomolar concentration range. The toxin also blocks L-type channels of rat β pancreatic cells, with an affinity 40 times lower. Although not studied in detail, evidence indicates that the toxin also blocks other types of HVA calcium channels, such as P and Q. No effect was observed on low-voltage-activated, T-type calcium channels. The significant homologies between ω-phonetoxin-IIA and the peptides of the ω-agatoxin-III family, and the overlapping inhibitory effects on calcium channels are discussed in terms of the structure-activity relationship.
Pfl�gers Archiv European Journal of Physiology, 1984
The membrane potential response of proximal tubular cells to changing HCO3 concentrations was mea... more The membrane potential response of proximal tubular cells to changing HCO3 concentrations was measured in micro-puncture experiments on rat kidney in vivo. No significant effect was noticed when luminal bicarbonate concentration was changed. Changing peritubular HCOg by substitution with C1-resulted in conspicuous membrane potential transients, which reached peak values after I00-200 ms and decayed towards near control with time constants of ~ 2 s. The polarity of the potential changes and the dependence of the initial potential deflections on the logarithm of HCO3 concentration suggest a high conductance of the peritubular cell membrane for HCO3 buffer, but not for CI-, SO 2-, or isethionate. At constant pH, tricot was estimated to amount to ~0.68. At constant Pco2, tHco; was even greater because of an additional effect of OH-or respectively H + gradients across the cell membrane. The secondary repolarization may be explained by passive net movements of K § and HCO~ across the peritubular cell membrane, which result in a readjustment of intracellular HCO3 to the altered peritubular HCO3 concentration. Application of carbonic anhydrase inhibitors in the tubular lumen reduced the initial potential response by one half and doubled the repolarization time constant. The same effect occurred instantaneously when the inhibitor was applied together with the HCO3 concentration step-in the peritubular perfusate. This observation demonstrates that membrane bound carbonic anhydrase is somehow involved in passive rheogenic bicarbonate transfer across the peritubular cell membrane, and suggests that HCO; permeation might occur in form of CO2 and OH-(or H § in opposite direction).
Biophysical Journal, 2009
The composition of ionic channels involved in electrogenesis of smooth muscle cells in arterioles... more The composition of ionic channels involved in electrogenesis of smooth muscle cells in arterioles of skeletal muscle is poorly understood. Here, we investigated inward currents responsible for the depolarizing phase of action potential. Although these currents are thought to be primarily through L-type Ca 2þ channels, action potentials recorded in our experiments with perforated patch technique were not eliminated by removal of extracellular Ca 2þ or by addition of L-type Ca 2þ channel blocker nifedipine (10 mM). Na þ channel blocker tetrodotoxin (TTX, 1 mM) abolished action potentials at low (~10 mM), but not normal (2 mM), extracellular Ca 2þ. When recorded with 140 mM Cs þ and 10 mM EGTA in the pipette and 145 mM Na þ and 2 mM Ca 2þ in the bath, the maximal whole-cell currents (at þ10 mM) were 2252 A/F, n¼6. The magnitude of slowly activating/inactivating currents that remained in the presence of 1 mM TTX was 451 A/F. Na þ currents recorded with 10 mM Ca 2þ in the bath were at least twofold smaller than those with~10 mM Ca 2þ. Na þ currents recorded through perforated patch at 2 mM Ca 2þ were reduced in the presence of 10 mM caffeine from 1953 to 954 A/F, n¼4. Our results suggest that TTX-sensitive voltage-gated Na þ channels contribute to depolarization of smooth muscle cells in skeletal muscle arterioles. Voltagegated Na þ channels appear to be under a tight control by intracellular Ca 2þ signaling.
Aplysia brasiliana is a n osmoconforming mollusc; the osmolality of its extracellular fluid follo... more Aplysia brasiliana is a n osmoconforming mollusc; the osmolality of its extracellular fluid follows that of the external media. This investigation analyzes the volume changes of isolated neuron bodies exposed to hypotonic shocks. The abdominal ganglion was isolated, and the volumes of neuron bodies as well as intracellular K' concentration were measured. Hypotonic shocks induce a rapid swelling followed by a slower restoration of cell volume. The regulatory volume decrease (RVD) restores cell volume to its control value. Ba2+ slows RVD without blocking it. Furosemide (in the pM range) completely and reversibly blocks the regulatory volume decrease. On return t o isotonic solution after RVD, cell shrinkage was only detected when furosemide was present. I t is concluded that neuron bodies of A. brasiliana display efficient processes for volume regulation, based on a conductive pathway and a furosemide-sensitive transport mechanism, which is probably the Na-2C1-K cotransporter. A model simulation provides additional support to this hypothesis.