Abstract 2313: PhKv a Spider Neurotoxin With Antiarrhythmogenic Action
The venom of the Brazilian spider Phoneutria nigriventer contain a cocktail of toxins that affect ionic channels (Gomez et al., 2002). One of them, PhKv reversibly inhibits A-type K+ current (IA) regulating Ca2+ oscillations in GH3. We investigated the effects of the native and recombinant PhKv spider toxin on cardiac arrhythmias during ischemia/reperfusion injury in isolated hearts and right atria. Purified PhKv contains 40 amino acids and a molecular weight of 4584 Daltons. Cardiac arrhythmias on isolated perfused heart were defined as the presence of ventricular tachycardia (VT) and/or ventricular fibrillation (VF). Electrogram and isometric tension signals were obtained by Biopac System. The typical stimulation protocol consisted of the application of pulse trains (250 bipolar voltage pulses, amplitude 1.5 × threshold, 0.2 ms duration, 8 mV) at 66.7 Hz. In control conditions, 1 to 5 trains of 5 s applied 0.5 min apart were sufficient to evoke arrhythmia at each trial. Right atria were perfused with KRS containing PhKv (84 nM) for 10 min before stimulation. All procedures followed the guidelines for the Use and Care of Animals for Research issued by the NIH. For the calcium transient, the isolated myocytes were incubated with 6.6 μM fluor-4 AM and stimulated (1Hz). Data were acquired under steady-state conditions with Zeiss LSM 510 META confocal microscope. The native and the recombinant PhKv had similar action decreasing by 55% the duration of arrhythmias in isolated rat hearts, (P<0.01). When applied one minute after the beginning of the reperfusion period PhKv attenuated the degeneration of VT to VF. PhKv caused a significant decrease in the duration of tachyarrhythmias and reduction in heart rate and increased QT interval (P<0.05). PhKv exhibited higher Ca2+ transient with no apparent effect on Ca2+ transient decay kinetics of ventricular cardiomycocytes. PhKv 30 nM increased cardiomyocyte shortening and this result correlates with the observation that PhKv increases peak Ca2+ amplitude in cardiomyocytes. The results shows that PhKv and its recombinant form have antiarrythmogenic effects in isolated rat hearts reducing the duration and incidence of arrhythmias.
Supported by Instituto do Milenio, CNPq and Fapemig.