Regulation of the renal Na-HCO3 cotransporter by cAMP and Ca-dependent protein kinases

Changes in the activity of the brush-border Na-H antiporter are accompanied by parallel changes in the activity of the Na-HCO3 cotransporter. Adenosine 3',5'-cyclic monophosphate (cAMP) and calmodulin inhibit the Na-H antiporter, whereas protein kinase C (PKC) stimulates it. We hypothesized that cAMP, calmodulin, and PKC should have similar effects on the Na-HCO3 cotransporter activity. Phosphorylated renal basolateral membranes were treated with either cAMP, calmodulin, or phorbol ester. cAMP, 1 microM, inhibited HCO3-dependent 22Na uptake without affecting 22Na uptake in presence of gluconate, suggesting that cAMP inhibits Na-HCO3 cotransporter activity without altering diffusive 22Na uptake. The effect of cAMP to inhibit the Na-HCO3 cotransporter could also be elicited by the catalytic subunit of cAMP, and this inhibitory effect was prevented by the protein kinase A (PKA) inhibitor. Calmodulin (1 microM), in presence of Ca, also inhibited HCO3-dependent 22Na uptake in presence of HCO3, whereas 22Na uptake in the presence of gluconate was unchanged. The inhibitory effect of calmodulin on HCO3-dependent 22Na uptake was prevented by N-(4-aminobutyl)-5-chloro-2-naphthalene sulfonamide (W-13), an inhibitor of calmodulin. Phorbol 12-myristate 13-acetate and PKC stimulated Na-HCO3 cotransporter activity, whereas the inactive analogue, 4 alpha-phorbol, failed to elicit such a stimulation. Basolateral membranes displayed cAMP-dependent and Ca-dependent protein kinase activities. Thus PKA and Ca-dependent protein kinases regulate the activity of the Na-HCO3 cotransporter and suggest that hormones that act through these systems modulate the activity of the Na-HCO3 cotransporter.