Endothelium-dependent relaxation of rat mesenteric arterial rings by a Phoneutria nigriventer venom fraction.

Phoneutria nigriventer spider venom has been described as acting on several cardiovascular sites. In the present paper, a semi-purified fraction of this spider venom was studied to observe any contractile or relaxing effect in rat mesenteric arterial rings (MAR). Spider venom was first fractionated by gel filtration and subsequently by gradual isocratic steps in 0.1% trifluoroacetic acid. The first fraction of this last fractionation step is studied in the present paper and due to its main effect, it was named NORF (nitric oxide releasing fraction). No direct contractile effect was induced by NORF in relaxed MAR, suggesting no NORF-induced neurotransmitter release in this preparation. No significant influence of NORF was observed on concentration-response curves to phenylephrine on endothelium-denuded MAR, but a significant inhibitory shift of concentration-respense curves was observed on endothelium-preserved MAR (EC50 = 0.39 +/- 0.07 microM for control and EC50 = 0.68 +/- 0.14 microM with NORF). NORF induced concentration-dependent relaxation in endothelium-preserved phenylephrine pre-contracted MAR but not in endothelium-denuded MAR. NORF-induced relaxation was inhibited by the nitric oxide synthase inhibitor L-NAME (N(omega)-nitro-arginine methyl ester). Indomethacin or HOE-140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin) had no significant effect on NORF-induced relaxation. Acetylcholine- and NORF-induced relaxation of pre-contracted MAR were differently inhibited by atropine. The pA2 value for atropine-acetylcholine was 9.78 +/- 0.06 and that for atropine-NORF was 8.53 +/- 0.30 (P<0.01). These observations suggest that NORF induces concentration-dependent liberation of nitric oxide from MAR endothelium and that a non-muscarinic mechanism might be involved in this effect. Our data suggest no involvement of prostanoids or bradykinin in the relaxing mechanism.

Phoneutria nigriventer omega-phonetoxin IIA blocks the Cav2 family of calcium channels and interacts with omega-conotoxin-binding sites.

omega-Phonetoxin IIA (omegaPtxIIA), a peptide from spider venom (Phoneutria nigriventer), inhibits high threshold voltage-dependent calcium currents in neurons. To define its pharmacological specificity, we have used patch-clamp methods in cell lines expressing recombinant Ca(v)2.1, Ca(v)2.2, and Ca(v)2.3 channels (P/Q-, N-, and R-type currents, respectively). Calcium currents generated by Ca(v)2.1 and Ca(v)2.2 were blocked almost irreversibly by 3 nm omegaPtxIIA, whereas Ca(v)2.3 showed partial and readily reversible inhibition. Binding assays with mono[(125)I]iodo-omegaPtxIIA indicated that membranes expressing recombinant Ca(v)2.1 or Ca(v)2.2 channels showed a single class of sites with similar affinity (K(D) approximately 50 pm), whereas low affinity interactions were detectable with Ca(v)2.3. Kinetic, saturation, and displacement assays demonstrated that rat brain synaptosomes displayed multiple classes of binding sites for (125)I-omegaPtxIIA. High affinity binding of (125)I-omegaPtxIIA was totally displaced by omegaPtxIIA (K(i) = 100 pm), but only partially by omega-conotoxin GVIA (25% inhibition) and omega-conotoxin MVIIC (50% inhibition at 0.3 microm). (125)I-omegaPtxIIA thus defines a unique high affinity binding site that is predominantly associated with Ca(v)2.1 or Ca(v)2.2 channels.

Epidemiological and clinical aspects of snakebite in Belo Horizonte, Southeast Brazil

Um estudo clinico-epidemiologico, comparando 310 pacientes hospitalizados por acidentes ofidicos (casos) e 310 pacientes hospitalizados por outras causas (controles), pareados por idade e sexo, durante um periodo de sete anos, foi conduzido em um hospital de emergencias em Belo Horizonte, MG. O diagnostico dos casos foi baseado no quadro clinico ou na identificacao do ofidio