The effects of gaboon viper (Bitis gabonica) venom on voltage-clamped single heart cells

The effects of crude B. gabonica venom on single ventricular myocytes from guinea-pig hearts were studied using the patch clamp technique in the 'whole cell' mode. Irreversible effects on the membrane currents, which became prominent within 15 min of venom application, were: (1) a decrease in the time invariant current (associated with the inward rectifying K+ current), most clearly seen over a voltage range negative to the resting membrane potential; and (2) a decrease in the peak inward current (associated with the Ca2+ current) elicited by steplike depolarizations from a holding potential of -40 mV. A transient increase in the peak inward current, which preceded its eventual decline, was also noticed; it peaked 6-10 min after the venom was applied. Application of the venom to unclamped, stimulated cells resulted in a shortening of the plateau phase and disturbances of the repolarization phase of action potentials. An early transient prolongation and elevation of the plateau was observed, occurring with the same time course of the transient increase in the peak inward current. No signs of damage to the cell membrane integrity, neither electrical (appearance of a leakage current) nor morphological (surface blebs, loss of striation pattern and of rodlike shape in the isolated myocytes), accompanied the effects observed on ionic currents and action potential activity, supporting the hypothesis of a selective cardiotoxic action of B. gabonica venom.