Synthesis of the calcium transport ATPase of sarcoplasmic reticulum and other muscle proteins during development of muscle cells in vivo and in vitro

Abstract

The effect of medium Ca 2+ concentration upon the concentration and the rate of synthesis of muscle proteins was investigated in chicken pectoralis muscle cultures. There is an easily identifiable class of muscle protein which includes the Ca 2+-ATPase of sarcoplasmic reticulum, myosin, troponin C, ATP : creatine phosphotransferase, muscle specific actin, tropomyosin 1 and 2, and muscle hemagglutinin, which show a large increase in concentration during normal development. The increased synthesis of these proteins was inhibited, without inhibition of cell proliferation, in culture media of relatively low Ca 2+ concentration, 0.05–0.3 mM, where fusion was prevented. Similar medium Ca 2+ concentration was required for the expression of all these proteins, suggesting their coordinate regulation. The proteins are denoted as ‘calcium-modulated proteins’. The increased Ca 2+ transport activity of sarcoplasmic reticulum in cultured chicken pectoralis muscle cells during development at 1.8 mM medium calcium concentration represents de novo synthesis of the Ca 2+ transport ATPase, as shown by immunoprecipitation, active site labeling and direct identification of the Ca 2+ transport ATPase on two-dimensional gel electropherograms of whole muscle homogenates. The concentration and the turnover rate of the majority of the muscle proteins is not affected significantly by medium Ca 2+ concentration between 0.06 and 1.8 mM. It is proposed that increase in cytoplasmic free Ca 2+ concentration during fusion plays a central role in the regulation of the synthesis of calcium-modulated proteins.