Antonio C. Cassola

• Associate professor
• Principal Investigator at University of São Paulo

The neurotoxicity of two secreted Phospholipases A2 from Brazilian coral snake venom in rat primary hippocampal cell culture was investigated. Following exposure to Mlx-8 or Mlx-9 toxins, an increase in free cytosolic Ca(2+) and a reduction in mitochondrial transmembrane potential (ΔΨm) became evident and occurred prior to the morphological changes...

Pulp of deciduous teeth contains mesenchymal stem cells originated from neural crest. These cells can be differentiated into several phenotypes (neuronal cells, adipocytes and odontoblasts). Functional expression of voltage-dependent channels (Na+ and K+) by these cells was investigated with special interest on the role of channels for the phenotyp...

Innumerous protocols, using the mouse embryonic stem (ES) cells as model for in vitro study of neurons functional properties and features, have been developed. Most of these protocols are short lasting, which, therefore, does not allow a careful analysis of the neurons maturation, aging, and death processes. We describe here a novel and efficient l...

Objective: The dorsal root ganglia (DRG) contains the pseudo-unipolar neurons of sensory input. Neuron somata is enveloped by satellite glial cells (SGC) whose functions is still unknow. To further unveil the sinalization between neurons and glia in DRG we have investigated the expression of purinergic metabotropic receptors (P2Y) by SGC of DRG.Met...

OBJECTIVES. It was previously shown that eugenol, a phenylpropene, blocks fast and reversibly voltage-gated Na+ channels (NaV), but little concern was given to the blocker binding to different conformational states of channel molecule. Here we reported a detailed analysis of state-dependent effects of eugenol on tetrodotoxin-resistant (TTX-R) NaV i...

Eugenol, a phenylpropene synthesized by many angiosperms, acts as atimicrobial toxin and has analgesic properties for humans. Here we show that EUG has a blocking action on tetrodotoxin-resistant voltage-gated sodium channels. The effects of eugenol and lidocaine were thoroughly compared. Currents were recorded in dorsal root ganglia neurons from n...

Crotamine is a peptide toxin from the venom of the rattlesnake Crotalus durissus terrificus that induces a typical hind-limb paralysis of unknown nature. Hind limbs have a predominance of fast-twitching muscles that bear a higher density of sodium channels believed until now to be the primary target of crotamine. Hypothetically, this makes these mu...

The presence of high voltage-activated calcium channels in the rat pineal gland is well known. However, their role in pineal metabolism is not completely understood and is even controversial. Better to understand this matter, we investigated the effects of L-, N- or P/Q-type calcium channel blockers (nifedipine, omega-conotoxin GVIA, omega-agatoxin...

Plasmodium vivax is the most widely distributed human malaria parasite and responsible for 70-80 million clinical cases each year and a large socio-economical burden. The sequence of a chromosome end from P. vivax revealed the existence of a multigene superfamily, termed vir (P. vivax variant antigens), that can be subdivided into different subfami...

The role of peripheral potassium channels on the antinociceptive effect of Crotalus durissus terrificus venom, a mixed delta- and kappa-opioid receptor agonist, was investigated in hyperalgesia induced by carrageenin or prostaglandin E(2). Rat paw pressure test was applied before and 3 h after the intraplantar (i.pl.) injection of the nociceptive s...

The electrical properties of Aplysia brasiliana myogenic heart were evaluated. Two distinct types of action potentials (APs) were recorded from intact hearts, an AP with a slow rising phase followed by a slow repolarizing phase and an AP with a 'fast' depolarizing phase followed by a plateau. Although these two APs differ in their rates of depolari...

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 n...

 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...

The mechanism of acidification in the cortical distal tubule of mammalian kidney was analysed by "in vivo" microperfusion and using MDCK cells in culture, by electrophysiological and by cell pH microfluorescence techniques. An electrogenic effect of the vacuolar H(+)-ATPase, which has been localized to the intercalated cells of the cortical distal...

The presence of an electrogenic H+-ATPase has been described in the late distal tubule, a segment which contains intercalated cells. The present paper studies the electrogenicity of this transport mechanism, which has been demonstrated in turtle bladder and in cortical collecting duct. Transepithelial PD (V t ) was measured by means of Ling-Gerard...

The article contains a brief review on the properties and classification of voltage-dependent Ca2+ channels and on the organic blockers of the different channel types. The effects of peptide toxins from the venoms of Conus sp and of the spider Agelenopsis aperta on high voltage-activated Ca2+ channels are discussed. In addition, we present prelimin...

Aplysia brasiliana is an 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 meas...

We have employed the patch-clamp technique to investigate the role of the actin cytoskeleton in the modulation of the low-conductance K+ channel in the apical membrane of the rat cortical collecting duct (CCD). This K+ channel is inactivated by application of cytochalasin B or D, both compounds known to disrupt actin filaments. The effect of both c...

The infusion of the dried roots of Bredemeyera floribunda Willd. is used in Brazilian popular medicine as a potent diuretic, especially in the treatment of hypertension and nephrolithiasis (renal calculi). Intravenous administration of crude root-extract (20-80 mg/kg) to anesthetized rats induces clear dose-dependent and reversible hypotensive resp...

The effect of arginine vasopressin (AVP) on the low-conductance K+ channel in the apical membrane of rat cortical collecting duct (CCD) principal cells from animals on a control and high-K+ diet was studied using patch-clamp techniques. AVP stimulated apical low-conductance K+ channel activity in both control and high-K+ animals: application of 110...

We used the patch-clamp technique to study the effects of arachidonic acid (AA) on the 35-pS secretory K+ channel in the apical membrane of rat cortical collecting duct (CCD). Application of 10 microM AA reversibly reduced channel activity to 1% of the control value [sum of open probability (NPo) decreased from 3.8 to 0.04]. AA inhibits the apical...

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...

The exposure of Aplysia brasiliana to dilute seawater (90 and 80%) caused an increase in relative weight, which returned to the original values after a few hours. Both osmotic and chloride concentrations of the hemolymph decreased on exposure to 80 and 90% dilute seawater, and after 3-h exposure there were no differences between the hemolymph and e...

The pH-stat technique has been used to measure H+ fluxes in gastric mucosa and urinary bladder “in vitro” while keeping mucosal pH constant. We now report application of this method in renal tubules. We perfused proximal tubules with double-barreled micropipettes, blocked luminal fluid columns with oil and used a double-barreled Sb/reference microe...

When the filtered load of buffers like bicarbonate or phosphate is increased by elevating GFR or buffer concentration in plasma, the overall renal reabsorption of bicarbonate or the formation of titratable acidity are markedly increased. The same happens when buffer concentration or flow rate are varied during proximal microperfusion. We have recen...

Cell membrane potentials of rat kidney proximal tubules were measured in response to peritubular ion substitutions in vivo with conventional and Cl- sensitive microelectrodes in order to test possible alternative explanations of the bicarbonate dependent cell potential transients reported in the preceding paper. Significant direct effects of bicarb...

The intracellular Cl− activity was determined in rat kidney proximal tubular cells in vivo, using single-barreled Cl− sensitive microelectrodes filled with Corning no. 477913 liquid ion exchanger resin to measureV Cl and using — in separate experiments — conventional KCl-filled microelectrodes to measure the membrane potential,V m. After correction...

Rabbit cortical thick ascending limb segments were perfused in vitro, and intracellular Cl- activity was estimated in three types of experiments using conventional and chloride selective microelectrodes. In series 1 Ringer like solutions were present on the two epithelial sides. In series 2 limen Cl- was replaced by gluconate, and in series 3 furos...

1. Renal cortical tubules of control and acetazolamide infused rats were perfused with 100 mM phosphate buffer at pH 5-5. The rate of alkalinization was measured by means of antimony micro-electrodes and was used to compute passive H ion fluxes from lumen to blood across the proximal and distal tubular epithelium. 2. The importance of other ionic m...

The loss of 32P-phosphate salts by the luminal compartment of cortical tubules was studied in control and in acetazolamide-infused rats, during stopped-flow microperfusion with 100 mM phosphate-raffinose solutions. When the initial pH of the perfusion solution was low (5.5), phosphate was lost more rapidly from proximal tubules than at high initial...

Microelectrodes for the determination of renal tubular fluid pH have been used since the work of Montgomery and Pierce (14) on the amphibian nephron. These authors as well as others (2, 3) used the quinhydrone electrode, where tubular fluid is aspirated into a micropipette and measured outside the tubular lumen, in general after equilibration with...