MYOSIN LIGHT-CHAIN PHOSPHORYLATION IN CARDIAC-HYPERTROPHY AND FAILUREDUE TO MYOCARDIAL-INFARCTION

The regulatory myosin light chain (MLC) is phosphorylated in cardiac m uscle by Ca2+/calmodulin dependent myosin light chain kinase (MLC) and is considered to play a modulatory role in the process of force gener ation, In order to determine changes in MLC phosphorylation in cardiac hypertrophy and heart failure, the relative content of MLCK and MLC p hosphorylation in the cardiac muscle from both sham control and experi mental rats were assessed at 4 and 8 weeks following ligation of the l eft coronary artery, Changes in the relative MLCK content were measure d by electrophoresis and immunoblot assay whereas phosphorylated and u nphosphorylated MLC were separated by non-denaturing 10% acrylamide/ur ea 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 res pective control values. The MLC phosphorylation increased significantl y in the right ventricle and septum but decreased markedly in the viab le left ventricle from 8-week experimental rats in comparison to the c ontrol values. No appreciable changes in the relative amount of MLCK a nd MLC phosphorylation were seen between control and experimental rats at 4 weeks. These results suggest duration and region specific change s in the levels of MLCK and MLC phosphorylation in cardiac hypertrophy and heart failure subsequent to myocardial infarction. (C) 1995 Acade mic Press Limited