Increasing the extracellular pH over the range pH 7.4-8.9 stimulated protein synthesis by about 60% in the rat heart preparation anterogradely perfused in vitro. Protein degradation was inhibited by this pH increase. The magnitudes of the effects at pH 8.9 on protein synthesis and degradation were similar to those of high concentrations of insulin. Cardiac outputs were increased, as were cardiac phosphocreatine contents, indicating that the alterations in extracellular pH did not adversely affect the physiological viability of the preparation. ATP contents were unaltered. The creatine kinase equilibrium was used to assess the magnitude of the change in intracellular pH induced by these treatments. The increase in intracellular pH was about 0.2 for a 1-unit increase in extracellular pH. Thus small changes in intracellular pH have dramatic effects on cardiac protein turnover.

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