Extracellular nucleotide receptor inhibits AVP-stimulated water permeability in inner medullary collecting duct

The P-2u class of nucleotide receptors is linked to mobilization of intracellular Ca2+ in many cell types, including the renal collecting duct cells. In the present studies, we examined the effects of nucleotides (ATP, UTP, and ADP; 10 mu M each) on the arginine vasopressin (AVP, 0.1 nM)-stimulated osmotic water permeability (P-f) in in vitro perfused terminal inner medullary collecting ducts (IMCD) of rat. ATP or UTP, when added to the bath, decreased the AVP-stimulated P-f by similar to 40%. These effects were reversible upon withdrawal of the nucleotides. However, addition of ADP to the bath or sham exchange of the bath had no significant effect on the P-f. Furthermore, ATP did not have any significant effect on the P-f stimulated either by a membrane-permeant, nonhydrolyzable adenosine 3',5'-cyclic monophosphate (cAMP) analogue [8-(4-chlorophenylthio)-cAMP, 0.1 mM] or by forskolin (1 mu M). In line with these findings, ATP decreased the AVP-stimulated cAMP levels in IMCD suspensions to similar to 68%. In addition, ATP did not exert an inhibitory effect on the AVP-stimulated P-f in the presence of calphostin C (150 nM), an inhibitor of protein kinase C. These results lead us to conclude the following: 1) agonist occupancy of the putative nucleotide receptor in the terminal IMCD causes an inhibition of AVP-stimulated P-f; and 2) this effect is due to a decrease in cellular cAMP levels, most likely resulting from activation of the phosphoinositide signaling pathway.