G-ALPHA-13 STIMULATES NA-H EXCHANGE

Activity of the ubiquitous Na-H exchanger (NHE1) is regulated by a number of receptors with tyrosine kinase activity as well as by several classes of receptors coupled to heterotrimeric GTP-binding proteins. We previously demonstrated that the beta(2)-adrenergic receptor and other receptors that stimulate adenylyl cyclase by activating G(s) stimulate NHE1 by a guanine nucleotide-dependent mechanism that is independent of receptor coupling to G(s). Now we report that a recently identified G alpha subunit, alpha 13, activates the exchanger. Transient expression of mutationally activated alpha 13 constitutively stimulates Na-H exchange; moreover, an alpha 13/alpha(z) chimera, designed to respond to stimulation by G(i)-coupled receptors, mediates stimulation of Na-H exchange by one such receptor, the dopamine(2), receptor. Mutationally activated alpha 13, however, does not stimulate adenylyl cyclase activity or phosphoinositide hydrolysis, indicating that its action on NHE1 occurs independently of these two effector pathways. These findings reveal the first known signaling function of alpha 13 and identify a new G protein involved in the regulation of NHE1.