Ca2+, crossbridge phosphorylation, and contraction.

Abstract

Ca2+ -calmodulin dependent phosphorylation of the 20,000-dalton myosin light chain by myosin light chain kinase (MLCK) and dephosphorylation by myosin light chain phosphatase (MLCP) are important regulatory mechanisms for smooth muscle contraction (47, 55, 87, 91). This review attempts to answer a specific question: Can Ca2+ -calmodulin dependent MLCK activa­ tion, per se, explain the steady-state and transient changes in crossbridge phosphorylation, isometric stress, and isotonic shortening velocity during smooth muscle contraction? We address this question by first considering the experimental data. A rather simple hypothesis that predicts changes in phosphorylation, isometric stress, and isotonic shortening velocity using MLCK activity as the input is then discussed (36, 37) .