G-PROTEIN STIMULATION INHIBITS AMILORIDE-SENSITIVE NA/H EXCHANGE INDEPENDENTLY OF CYCLIC-AMP

G-proteins are heterotrimeric proteins involved in many transmembrane signaling events. Both the renal basolateral membrane and the renal brush border membrane contain large quantities of these proteins. G-proteins appear related to hormonal signaling in the basolateral membrane and presumably affect ion gating in the brush border. We investigated the influence of G-proteins on the amiloride-sensitive Na/H exchanger, the activity of which is regulated at least in part by cAMP-dependent protein kinase, by measuring the amiloride-sensitive component of [Na-22(+)] uptake in rat renal brush border membrane vesicles (BBMV) in the presence of a pH gradient. Incubation of vesicles with AlF4- (10-mu-M Al3+, 10 mm F-) resulted in significant inhibition of amiloride-sensitive [Na-22(+)] uptake at both 20 seconds and 5 minutes of incubation. Incorporation of GTP-gamma-S into BBMV by transient hypotonic lysis also resulted in significantly reduced amiloride-sensitive [Na-22(+)] uptake compared to controls at both time points. This inhibition could be reversed by GDP-beta-S. Similar lysis in the presence of 10-mu-M GDP-beta-S alone had no significant effect. When Na+-dependent [C-14]-D-glucose uptake into BBMV was studied no significant effect of these G-protein modulating agents was observed. Adenylate cyclase activity could not be stimulated in these BBMV preparations using standard techniques. Furthermore, cAMP-dependent protein kinase activity, strongly stimulated in these BBMV by exogenously added cAMP, was not stimulated by 10-mu-M GTP-gamma-S alone. These findings suggest that the amiloride-sensitive Na/H exchanger can be regulated by G-proteins independently of adenylate cyclase and cAMP-dependent protein kinase.