Synthesis of shock proteins in cultured fetal mouse myocardial cells

We examined the synthesis of shock proteins in cultured fetal mouse myocytes. The preparation is free from fibroblasts, and the cells are vital and morphologically intact with respect to beat frequency and electron microscopy. Cultured myocytes from fetal mouse heart respond to heat shock and cadmium chloride, H2O2, allylamine, cyclosporine, and azathioprine exposure with the synthesis of shock proteins. Heat shock induces the de novo synthesis of two proteins of 71 and 68 kDa; cadmium chloride induces, in addition, a protein of 30 kDa. The other substances tested provoke the synthesis only of the 30-kDa polypeptide. The formation of heat shock proteins is concentration-dependent: Cyclosporine provokes the de novo synthesis of the 30-kDa polypeptide at concentrations above 10 ng/ml, whereas azathioprine causes the same effect at concentrations above 50 micrograms/ml. Hence cyclosporine might be cardiotoxic already at concentrations below the pharmacological dosages while azathioprine influences the myocytes only at concentrations much higher than the therapeutic level. Our results indicate that heat shock protein expression in cultured myocytes may be a useful tool to monitor cardiotoxicity.