Different effects of reducing agents on omega-conotoxin GVIA inhibition of [H-3]-acetylcholine release from rat cortical slices and guinea-pig myenteric plexus

1 The effect of reducing reagents on omega-conotoxin GVIA (omega-CgTX) inhibition of the release of [(3)]-acetylcholine ([H-3]-ACh) induced by tityustoxin, K+ 50 mM and electrical stimulation was investigated in rat brain cortical slices. 2 In cortical slices the inhibition of tityustoxin or electrically-stimulated [H-3]-ACh release by omega-CgTX was dramatically increased by reducing reagents ascorbate or beta-mercaptoethanol. Dehydroascorbic acid did not substitute for ascorbate. 3 Depolarization induced by K+ 50 mM caused [H-3]-ACh release from cortical slices which was not inhibited by omega-CgTX, even in the presence of ascorbate. 4 In the guinea-pig myenteric plexus, omega-CgTX inhibition of the tityustoxin induced release of [H-3]-ACh was independent of ascorbate. 5 It is suggested that N-type-like calcium channels in guinea-pig myenteric plexus may have pharmacological/biochemical diversity from similar channels of rat cerebral cortex.