Characterization of the Phosphoprotein Profile in Spontaneously Beating Cultured Rat Heart Cells

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Abstract
Culture of neonatal rat hearts yields a fairly homogeneous population of synchronous and spontaneously beating myocardial cells. Incubation of the culture with 32Pi followed by polyacrylamide gel electrophoresis and autoradiography yields a reproducible profile of both high and low MW phosphoproteins. This phosphoprotein profile is clearly distinct from that observed with mesenchymal cells, the major contaminant of the heart cell cultures. By comparison with purified standard proteins and by copurification with neonatal rat myosin, one of these phosphoproteins was identified as the 20,000-dalton myosin L chain. The demonstration of phosphoproteins in intact contracting myocardial cells provides a system to study the complex interaction of the phosphoproteins involved in the control of cardiac contractility.