Protein kinase C-dependent and -independent activation of Na+/H+ exchanger by G alpha 12 class of G proteins.

Abstract

Constitutively activated mutants of the Gal, class of G proteins, Gal,(Q229L) and Gal,(Q226L), were transiently expressed in COS-1 cells, and the activity of amiloridesensitive Na+/H+ exchanger was measured. The expression of either GaJQ229L) or Gal,(Q226L) increased the basal activity of the amiloride-sensitive exchanger by "fold. Regulation of this activation by other G protein signaling pathways was investigated by the transient expression of constitutively activated G protein mutants of Ga,(Q227L), Ga,(Q2OSL), and Gaq(Q209L) in COS-1 cells. Only Gaq showed a similar activation of the exchanger. Chronic treatment of the transfected cells with 4fl-phorbol 12-myristate 13-acetate to deplete the endogenous protein kinase C completely inhibited the activation of the antiporter by Gal,(Q229L), whereas activation by Ga,,(Q226L) remained unaffected. These results indicated that both Gal, and Gal, can activate Na+/H+ exchanger by two distinct signaling pathways. Ga,, activation of the exchanger was dependent on protein kinase C pathway, whereas Gal, activation was not. These studies define the involvement of Gal, class of G proteins, for which no function has been assigned yet, in the activation of Na+/H+ exchanger.