Adenine-induced inhibition of Na+-ATPase activity: Evidence for involvement of the Gi protein-coupled receptor in the cAMP signaling pathway

In the present work, we demonstrate that adenine reduced Na+-ATPase activity in isolated basolateral membrane (BLM) of proximal tubule in a dose-dependent manner. Adenine metabolism was ruled out by TLC analysis of the potential [3H]adenine derived-metabolites. Specific binding of [3H]adenine to isolated BLM was observed in a dose-dependent manner with Kd and Bmax of 242.6 ± 27.6 nM and 2749.9 ± 104.9 fmol mg−1, respectively. Adenine increased the [35S]GTPγS specific binding and it was completely abolished by 10−6 M GDPβS (G protein inhibitor) but it was not modified by DPCPX, DMPX and MRS1523, selective antagonists for A1, A2 and A3 receptors, respectively. Furthermore, the inhibitory effect of adenine on the Na+-ATPase activity was blocked by 10−6 M GDPβS, 1 μg/ml pertussis toxin (Gi protein inhibitor), 10−6 M foskolin (adenylyl cyclase activator) and 10−8 M cAMP. These data demonstrate that adenine inhibits the proximal tubule Na+-ATPase activity through the Gi protein-coupled receptor.