Synthetic omega-conotoxin: a potent calcium channel blocking neurotoxin.

The Ca2+ channel blocking action of synthetic omega-conotoxin (omega CTX) was studied on isolated frog dorsal root ganglion neurons using a 'concentration clamp' technique which enabled internal perfusion and rapid external solution change. At 100 nM, omega CTX showed a time-dependent depression of Ca2+ current (ICa). At higher concentrations, omega CTX exhibited a dose-dependent depression of ICa amplitude without changing the current-voltage relationship. Increases in external Ca2+ concentration partly overcame the inhibitory action of omega CTX on the ICa amplitude. At 10 microM omega CTX totally blocked ICa without effect on the Na+ current. It was likely that omega CTX had high selectivity for the Ca2+ channel.