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R S Leite

Publications and source records attributed to R S Leite.

8 recordsLinked to original sources
PubMed2006

The effect of the myotoxic Lys49 phospholipase A(2) from Agkistrodon contortrix laticinctus snake venom on Na+/K+ -ATPase activity of toad bladders.

ACLMT is a myotoxic Lys49 phospholipase A(2) isolated from the venom of the snake Agkistrodon contortrix laticinctus. We have previously shown that ACLMT increases baseline water transport and partially inhibits vasopressin-stimulated water transport across toad bladders due to an increase in cytosolic calcium. However, these evidences provide insufficient insight into the mechanisms involved in the effects of ACLMT on membrane permeability. In an attempt to better understand such mechanisms, the current study aimed to investigate whether the Na(+)/K(+)-ATPase activity of isolated toad bladders can be affected by the ACLMT and the synthetic peptide from its C-terminal region. The toxin significantly decreased the Na(+)/K(+)-ATPase, while the peptide did not alter it. These findings suggest that the effects of ACLMT on membrane permeability may be due to the inhibition of the Na(+)/K(+)-ATPase activity, and that the C-terminal region may not play a relevant role in this effect. This study contributes toward a better understanding of the mechanisms involved in the toxicity of the snake venom Lys49 PLA(2) myotoxins on biological tissues.

Agkistrodon↗
PubMed2004

Effects of a myotoxic Asp49 phospholipase A2 (ACL-I PLA2) isolated from Agkistrodon contortrix laticinctus snake venom on water transport in the isolated toad urinary bladder.

An Asp49 PLA2 (ACL-I PLA2) was purified from the venom of Agkistrodon contortrix laticinctus by gel filtration and cation-exchange chromatography. It has a relative molecular mass of 14,000, and its N-terminal sequence has more than 65% of identity with other snake venom PLA2s. ACL-I PLA2 injected into the Tibialis anterior muscle of rats and mice at doses of 0.3 and 1.6 mg/kg, respectively, induced muscle fiber necrosis, cellular infiltration and edema 3 and 48 h after injection. The effect of the purified enzyme on water permeability was tested in the isolated toad urinary bladder. Water flow through the membrane was measured gravimetrically in bag preparations of the bladder. ACL-I PLA2 (20 nM) did not significantly alter the water permeability in the bladder preparations, whereas ACL myotoxin (ACLMT), a Lys49 PLA2 isolated from the same venom, at similar concentration significantly increased (81%) the water permeability. However, both toxins inhibited the AVP-stimulated water permeability. These results strongly suggest that PLA2 activity is not involved in the ACLMT effect on water transport and the effect of ACL-I PLA2 myotoxin on membrane permeability is mediated by mechanisms that are different in comparison to ACLMT.

Agkistrodon↗
PubMed2004

Effects of ACL myotoxin, a Lys49 phospholipase A(2) from Agkistrodon contortrix laticinctus snake venom, on water transport in the isolated toad urinary bladder.

ACL myotoxin (ACLMT) is a Lys49 phospholipase A(2)-like protein isolated from the venom of the snake Agkistrodon contortrix laticinctus. The aim of this work was to study the effect of ACLMT on water transport in the toad bladder. Water flow through the membrane was measured gravimetrically in bag preparations of the bladder. ACLMT (20 nM) increased the baseline water flow and partially inhibited arginine-vasopressin (AVP), 8-chlorophenylthio-cAMP (8-CPT-cAMP) and forskolin-stimulated water flow. The effect of ACLMT on baseline or AVP-stimulated water flow was prevented by lanthanum (0.1 mM) indicating that the effect of ACLMT on water transport may be mediated through an increase in intracellular calcium. The effect of ACLMT on baseline water flow was also prevented by nifedipine (0.1 mM) indicating the participation of exogenous calcium in this effect. Carbachol (0.1 mM) has been shown to enhance baseline water flow while inhibiting AVP-stimulated water flow. The effects of ACLMT and carbachol on baseline water flow and AVP-stimulated water flow were not additive, suggesting that both agents alter water transport by a similar mechanism. Indomethacin (10 microM) reduced the effect of ACLMT on forskolin-stimulated water flow, suggesting an increase in prostaglandin biosynthesis. These results suggest that the effects of ACLMT on water transport may be mediated by increasing intracellular calcium and stimulation prostaglandin biosynthesis.

Agkistrodon↗
PubMed2004

Effect of a recombinant Lys49PLA2 myotoxin and Lys49PLA2-derived synthetic peptides from Agkistrodon species on membrane permeability to water.

The aim of this work was to study the effect of recombinant ACL myotoxin, a Lys49PLA2 from Agkistrodon contortrix laticinctus snake venom and Lys49PLA2-derived synthetic peptides corresponding to the region 115-129 of venom of the two different Agkistrodon species on water permeability in the toad urinary bladder. The water flow through the membrane was measured gravimetrically in bag preparations of the bladder. The addition of recombinant ACL myotoxin-MBP (maltose binding protein) fusion protein (10 nM) to the bathing solution significantly increased (above 60%) the water transport compared with the control hemibladders. The addition of the Lys49PLA2-derived synthetic peptides in several concentrations to the bathing solution did not affect the water transport across membrane. These results suggest that the ACL myotoxin effect on water transport is not related to the cytotoxic C-terminal region.

Agkistrodon↗
PubMed2001

Effects of cholinergic agents on the vasopressin-mediated water transport in the isolated toad bladder.

The aim of this work was to study the effect of some pharmacological cholinergic agents on the events that follow the interaction of arginine vasopressin with toad bladder membrane receptors related to synthesis of 3'5'(c)AMP. The water flow through the membrane was measured gravimetrically in sac preparations of the membrane. In the absence of arginine vasopressin (AVP), carbachol induced a significant increase in the water flow (37%) related to the basal (Ringer's solution). On the other hand, when carbachol and AVP were associated, a significant decrease of AVP hydrosmotic activity occurred (23%). The inhibitory effect of carbachol on the AVP action was almost completely abolished by the cholinergic antagonists atropine, pirenzepine, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) and the calcium antagonist lanthanum. Similarly, when carbachol and 3'5' cyclic adenosine monophosphate (3'5'(c)AMP) were associated, a decrease of nucleotide hydrosmotic activity was observed (12.80%). This effect was partially restored by the addition of pirenzepine or 4-DAMP in the bath solution. These results suggest a role for muscarinic receptors of sub-type M(1) and M(3), which are involved in the intracellular calcium release. The increase of calcium concentration in the intracellular medium acts as a negative modulator in the hydrosmotic action of antidiuretic hormone.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2001

Effectiveness of primary angioplasty in the treatment of acute myocardial infarction. Analysis of in-hospital and late outcomes in 135 consecutive cases.

OBJECTIVE: Evaluate early and late evolution of patients submitted to primary coronary angioplasty for acute myocardial infarction. METHODS: A prospective study of 135 patients with acute myocardial infarction submitted to primary transcutaneous coronary angioplasty (PTCA). Success was defined as TIMI 3 flow and residual lesion <50%. We performed statistical analyses by univariated, multivariated methods and survival analyze by Kaplan-Meier. RESULTS: PTCA success rate was 78% and early mortality 18,5%. Killip classes III and IV was associated to higher mortality, odds ratio 22.9 (95% CI: 5,7 to 91,8) and inversely related to age <75 years (OR = 0,93; 95% CI: 0.88 to 0.98). If we had chosen success flow as TIMI 2 and had excluded patients in Killip III/IV classes, success rate would be 86% and mortality 8%. The survival probability at the end or study, follow-up time 142 +/- 114 days, was 80% and event free survival 35%. Greater survival was associated to stenting (OR = 0.09; 0.01 to 0.75) and univessel disease (OR = 0.21; 0.07 to 0.61). CONCLUSION: The success rate was lower and mortality was higher than randomized trials, however similar to that of non randomized studies. This demonstrated the efficacy of primary PTCA in our local conditions.

Aged↗