Myosin light chain phosphorylation in cardiac hypertrophy and failure due to myocardial infarction

The regulatory myosin light chain (MLC) is phosphorylated in cardiac muscle by Ca2+/calmodulin dependent myosin light chain kinase (MLCK) and is considered to play a modulatory role in the process of force generation. In order to determine changes in MLC phosphorylation in cardiac hypertrophy and heart failure, the relative content of MLCK and MLC phosphorylation in the cardiac muscle from both sham control and experimental rats were assessed at 4 and 8 weeks following ligation of the left coronary artery. Changes in the relative MLCK content were measured by electrophoresis and immunoblot assay whereas phosphorylated and unphosphorylated MLC were separated by non-denaturing 10% acrylamide/urea gel and identified by Western blotting. The relative amount of MLCK was increased by 20-35% in the viable left ventricle, right ventricle and septum from the 8-week experimental rats in comparison to the respective control values. The MLC phosphorylation increased significantly in the right ventricle and septum but decreased markedly in the viable left ventricle from 8-week experimental rats in comparison to the control values. No appreciable changes in the relative amount of MLCK and MLC phosphorylation were seen between control and experimental rats at 4 weeks. These results suggest duration and region specific changes in the levels of MLCK and MLC phosphorylation in cardiac hypertrophy and heart failure subsequent to myocardial infarction.