Transitions in human atrial and ventricular myosin light-chain isoenzymes in response to cardiac-pressure-overload-induced hypertrophy

Abstract

The L chain subunits of human atrial and ventricular cardiac muscle were examined by 2-dimensional polyacrylamide-gel electrophoresis and limited proteolytic digestion. The L chain patterns in the normal right and left atria were identical. Myosin preparations isolated from right to left atria that were subjected to cardiac pressure overload-induced hypertrophy also contained ventricular L chain subunits. These were identified by peptide mapping in sodium dodecyl sulfate. Ventricular L chain-2 was the major species in hypertrophied atria, although L chain-1 subsequently appeared in severe pressure overload-hypertrophied cases. Evidence is presented for the existence of more than one form of ventricular L chain-2. The transition from atrial to ventricular myosin L chains correlated with the degree of pressure-overload hypertrophy in 83 examples of surgically excised atria. The adult atrial L chain-1 was shown to be homologous to the human fetal ventricular L chain-1 [Price, Littler and Cummins (1980)] by peptide mapping. A scheme of atrial/ventricular myosin L chain isoenzyme transitions is discussed in relation to changing contractile properties in cardiac muscle, together with implications for the role of L chain subunits.