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 [²²Na⁺] uptake in rat renal brush border membrane vesicles (BBMV) in the presence of a pH gradient. Incubation of vesicles with AlF₄^- (10 μM Al³⁺, 10 mM F^-) resulted in significant inhibition of amiloride-sensitive [²²Na⁺] uptake at both 20 seconds and 5 minutes of incubation. Incorporation of GTPγS into BBMV by transient hypotonic lysis also resulted in significantly reduced amiloride-sensitive [²²Na⁺] uptake compared to controls at both time points. This inhibition could be reversed by GDPβS. Similar lysis in the presence of 10 μM GDPβS alone had no significant effect. When Na⁺-dependent [¹⁴C]-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 μM GTPγS 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.