Direct inhibitory effects of some ‘calcium‐antagonists’ and trifluoperazine on the contractile proteins in smooth muscle

Abstract

1 Taenia preparations from the guinea-pig caecum were treated with Triton X-100 and glycerol to disrupt the plasma membrane. Disruption of the sarcolemma was confirmed by electronmicroscopy. The preparations contracted in response to low concentration of Ca²⁺ (10–40 μM) and the contractions were dependent upon exogenous adenosine triphosphate (ATP). 2 Nifedipine (100 μM), verapamil (100 μM) and diltiazem (100 μM) did not inhibit Ca²⁺-induced activation of the contractile proteins. 3 In contrast, fendiline (100 μM), cinnarizine (100 μM), flunarizine (100 μM), pimozide (100 μM) and trifluoperazine (100 μM) significantly inhibited Ca²⁺-induced contractions. The effects of cinnarizine (100 μM) were reversible. 4 These findings disclose further differences between calcium-antagonists and suggest that certain of these agents have an intracellular site of action.