Verrucotoxin inhibits K ATP channels in cardiac myocytes through a muscarinic M 3 receptor-PKC pathway

Abstract

Verrucotoxin is the major component of venom from the stonefish ( Synanceia verrucosa). Stings from the dorsal spines of the stonefish produce intensive pain, convulsions, hypotension, paralysis, respiratory weakness and collapse of the cardiovascular system, occasionally leading to death. It has been reported that verrucotoxin might modulate ATP-sensitive K + (K ATP) current in frog atrial fibers. However, the mechanism by which verrucotoxin acts on K ATP current remains unclear. In this study, we examined whether verrucotoxin inhibited K ATP current in guinea pig ventricular myocytes, using the patch clamp method. Verrucotoxin suppressed K ATP current induced by pinacidil (K ATP channel opener) in a concentration-dependent manner, with a half maximum concentration of 16.3 μg/ml. The effect of verrucotoxin on K ATP current was suppressed by atropine (1 μM), a muscarinic receptor antagonist, or by 4-diphenylacetoxy- N-methylpiperidine (100 nM), a muscarinic M 3 receptor antagonist. Furthermore, the effect of verrucotoxin on K ATP current was attenuated by the protein kinase C (PKC) inhibitor chelerythrine (10 μM) and calphostin C (10 μM), yet not by the cAMP-dependent protein kinase (PKA) inhibitor H-89 (0.5 μM). These results suggest that verrucotoxin inhibits K ATP current through the muscarinic M 3 receptor-PKC pathway. These findings enhance our understanding of the toxic effects of verrucotoxin from the stonefish.