Effect of acute overload on protein synthesis in cardiac muscle microsomes

Abstract

Acute overload in the isolated perfused heart results in increased incorporation of labeled amino acids into cardiac protein. Protein synthesis by microsomes, isolated from overloaded guinea pig left ventricles, was studied in a cell-free system using lysine-14c and leucine-14c. Control and overloaded hearts were perfused with ventricular flows of 7 ml/min. for 1-3 hr. with average aortic systolic pressures of 30 mm Hg in controls and 60 mm Hg in the stressed hearts. Microsomes from the overloaded left ventricles incorporated more than twice the amount of lysine-14c or leucine-14c into protein than the controls (515[plus or minus]30 compared to 213[plus or m inus] 10 counts/ min/mg protein N). Cross-incubation studies showed that microsomes from stressed ventricles did not lose their capacity to synthesize protein when incubated in control cell sap. Control microsomes, incubated in cell sap from overloaded ventricles, were not stimulated to increase incorporation of labeled amino acids into protein. Acute cardiac overload stimulates augmented microsomal protein synthesis independent of the source of cell sap or substrate as early as 1 hr. after onset of the stress. The specific part of the microsome affected remains to be clarified.