Regulation of Na+-H+ exchange in cultured opossum kidney cells by parathyroid hormone, atrial natriuretic peptide and cyclic nucleotides.

The activity of Na+-H+, exchange was studied in a cultured cell line derived from opossum kidney (OK cells). The activity of the exchanger was measured either as the amiloride (2 mM) inhibitable 22Na flux in acid-loaded cells, or as the Na+-dependent and amiloride-sensitive recovery of intracellular pH (pHi) from an acid load. Initial rates of tracer flux were analyzed in confluent monolayers while changes in pHi were evaluated in suspensions of trypsinized cells which had been loaded with 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein. Both 8-bromo-cAMP and 8-bromo-cGMP inhibit the activity of the exchanger in a dose-dependent manner. Maximal inhibition due to 8-bromo-cAMP was about 50% and was attained with 0.75 mM of the cyclic nucleotide. Parathyroid hormone (10(-9)-10(-7) M) and atrial natriuretic peptide (10(-7) M) also inhibit the activity of the exchanger. By measuring the rate of Na+-dependent pHi recovery from different starting pHi values, evidence was obtained for a cyclic nucleotide-dependent decrease in the response of Na+-H+ exchange to intracellular acidification. We conclude that cAMP and cGMP are intracellular messengers in the hormone-dependent regulation of Na+-H+ exchange activity in renal epithelial cells.