Epidermal growth factor and cyclic AMP stimulate Na+/H+ exchange in isolated rat hepatocytes

Na+/H+ exchange in acid-loaded isolated hepatocytes was measured using the intracellular pH indicator biscarboxyethyl-carboxyfluorescein (BCECF) to follow intracellular pH (pHi). The rate of amiloride-sensitive Na(+)-dependent recovery from cytoplasmic-acid-loading was found to be increased in cells treated with epidermal growth factor (EGF), 8-(4-chlorophenylthio)adenosine 3',5'-monophosphate (ClPhScAMP) or phorbol 12-myristate 13-acetate (PMA). These three agents increased the rate of Na+/H+ exchange to similar extents and their effects were not additive. The stimulation was shown in all three cases to be due an alkaline shift of 0.1 in the set point pH of the Na+/H+ exchanger. Experiments measuring the uptake of 22Na+ into acid-loaded primary hepatocyte monolayer cultures confirmed these results. EGF, ClPhScAMP and PMA significantly increased the amiloride-inhibitable accumulation of 22Na+, thus providing further evidence that Na+/H+ exchange is stimulated by these effectors.