Amino acid transport and protein synthesis in energetically-stable calcium-tolerant isolated cardiac myocytes

Abstract

Myocytes isolated by enzymic dispersion from adult rat ventricular tissue are shown to be energetically stable in the presence of 0.5 mM CaCl 2. ATP and ADP content and rates of lactate production are comparable with those of intact myocardial tissue and consistent with these cells being tightly coupled. Addition of 2,4-dinitrophenol precipitates rapid changes in adenine nucleotide concentrations and a 10-fold increase in lactate production. Cardiac myocytes selectively transport neutral amino acids of the A and L classes. Transport of the amino acid analogue α-aminoisobutyric acid is an active, temperature-dependent and insulin-sensitive process. The apparent K m for α-aminoisobutyric acid transport is similar to that determined for embryonic cardiac cells. Mature myocytes incorporate labelled amino acids into cytoplasmic proteins with molecular weights ranging from 10 000 to 150 000. Newly synthesised protein is metabolically stable. The data establishes calcium-tolerant myocytes as an experimental system offering many advantages over whole hearts for short- and long-term studies of protein synthesis and catabolism.