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

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 microM) and the contractions were dependent upon exogenous adenosine triphosphate (ATP). 2 Nifedipine (100 microM), verapamil (100 microM) and diltiazem (100 microM) did not inhibit Ca2+-induced activation of the contractile proteins. 3 In contrast, fendiline (100 microM), cinnarizine (100 microM), flunarizine (100 microM), pimozide (100 microM) and trifluoperazine (100 microM) significantly inhibited Ca2+-induced contractions. The effects of cinnarizine (100 microM) were reversible. 4 These findings disclose further differences between calcium-antagonists and suggest that certain of these agents have an intracellular site of action.