Inhibition of Ca2+-activated tension and myosin light chain phosphorylation in skinned smooth muscle strips by the phenothiazines

Abstract

The antipsychotic phenothiazine drugs trifluoperazine, chlorpromazine, and promethazine inhibited Ca²⁺-activated tension in functionally skinned rabbit ileum and rabbit pulmonary artery strips. Exogenous calmodulin rapidly reversed the inhibition of tension. Inhibition of the endogenous myosin light chain kinase by these drugs resulted with ATP or its analog, ATPγS, as a substrate. The evidence presented suggests the inhibition of Ca²⁺ activation of tension in skinned smooth muscle preparations by phenothiazines is due to the inhibition of Ca²⁺-activated phosphorylation of the 20,000 dalton myosin light chain by the endogenous myosin light chain kinase.