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

The effect of reducing reagents on ω‐conotoxin GVIA (ω‐CgTX) inhibition of the release of [ 3 H]‐acetylcholine ([ 3 H]‐ACh) induced by tityustoxin, K + 50 m m and electrical stimulation was investigated in rat brain cortical slices. In cortical slices the inhibition of tityustoxin or electrically‐stimulated [ 3 H]‐ACh release by ω‐CgTX was dramatically increased by reducing reagents ascorbate or β‐mercaptoethanol. Dehydroascorbic acid did not substitute for ascorbate Depolarization induced by K + 50 m m caused [ 3 H]‐ACh release from cortical slices which was not inhibited by ω‐CgTX, even in the presence of ascorbate. In the guinea‐pig myenteric plexus, ω‐CgTX inhibition of the tityustoxin induced release of [ 3 H]‐ACh was independent of ascorbate. 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.British Journal of Pharmacology (1997) 120 , 88–92; doi: 10.1038/sj.bjp.0700873