Actions of Ca²⁺ antagonists on the guinea-pig ileal myenteric plexus preparation

The guinea-pig ileal myenteric plexus preparation has been used to compare the actions of three Ca²⁺ channel antagonists, D 600 (methoxyverapamil), nicardipine and diltiazem, on smooth muscle contractions and acetylcholine release in response to electrical stimulation. Acetylcholine release was not affected by these agents at concentrations of 10^-6-10^-5 M. In confirmation of previous work, however, the smooth muscle contractile responses were effectively inhibited at these concentrations. Quercetin, a non-Ca²⁺ channel antagonist, was approximately equieffective in blocking both acetylcholine release and smooth muscle contractions. These data suggest that differences may exist in the antagonist sensitivity of voltage-dependent Ca²⁺ channels.