PROTEIN-KINASE C-DEPENDENT AND C-INDEPENDENT ACTIVATION OF NA+ H+ EXCHANGER BY G-ALPHA(12) CLASS OF G-PROTEINS/

Constitutively activated mutants of the G alpha(12) class of G protein s, G alpha(12)(Q229L) and G alpha(13)(Q226L), were transiently express ed in COS-1 cells, and the activity of amiloride-sensitive Na+/H+ exch anger was measured. The expression of either G alpha(12)(Q229L) or G a lpha(13)(Q226L) increased the basal activity of the amiloride sensitiv e exchanger by 2-5 fold. Regulation of this activation by other G prot ein signaling pathways was investigated by the transient expression of constitutively activated G protein mutants of G alpha(s)(Q227L), G al pha(i2)(Q205L), and G alpha(q)(Q209L) in COS-1 cells. Only G alpha(q) showed a similar activation of the exchanger. chronic treatment of the transfected cells with 4 beta-phorbol 12-myristate 13-acetate to depl ete the endogenous protein kinase C completely inhibited the activatio n of the antiporter by G alpha(12)(Q229L), whereas activation by G alp ha(13)(Q226L) remained unaffected. These results indicated that both G alpha(12) and G alpha(13) can activate Na+/H+ exchanger by two distin ct signaling pathways. G alpha(12) activation of the exchanger was dep endent on protein kinase C pathway, whereas G alpha(13) activation was not. These studies define the involvement of G alpha(12) class of G p roteins, for which no function has been assigned yet, in the activatio n of Na+/H+ exchanger.