Na-H exchange regulates intracellular pH in isolated rat hepatocyte couplets

Intracellular pH (pHi) was measured directly in isolated rat hepatocyte couplets using pH sensitive microelectrodes. The hepatocytes were maintained in a minimal salt buffer without added hormones or serum. Values of pHi (6.99 +/- 0.12, mean +/- SE) were close to their Nernst equilibria. After intracellular acidification with ammonium chloride, pH regulation was inhibited with 1 mM amiloride or by omission of external sodium, consistent with a Na-H exchange mechanism. Mean intracellular buffering power, in the nominal absence of carbon dioxide, was 34.1 +/- 11.4 mM. In the presence of external bicarbonate, amiloride or omission of sodium slowed, but did not completely inhibit recovery from acidification, indicating that additional pHi regulation mechanisms may operate in this preparation. These studies provide a direct measurement of pHi in hepatocyte couplets and indicate that Na-H exchange, together with a bicarbonate dependent system are important mechanisms for pHi regulation in this preparation.