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 (pH_i) from an acid load. Initial rates of tracer flux were analyzed in confluent monolayers while changes in pH_i 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 pH_i recovery from different starting pH_i 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.