Adenylyl cyclase is involved in desensitization and recovery of ATP- stimulated Cl^- secretion in MDCK cells

We investigated the process of and recovery from desensitization of the P₂ receptor-mediated stimulation of Cl^- secretion in Madin-Darby canine kidney (MDCK) cell monolayers by assaying the response of short-circuit current (I(sc)). When the cells were exposed to repeated 3-min challenges of ATP or UTP interspersed with 5-min washes, the response of I(sc) desensitized rapidly followed by spontaneous recovery. The pattern of inhibition by various channel blockers or enzyme inhibitors revealed that both the initial and recovered responses of I(sc) have the same ionic and signaling mechanisms. The desensitization and recovery processes were confined to the membrane exposed to the repeated challenges. When added during the desensitized phase, 8-bromoadenosine 3',5'-cyclic monophosphate enhanced the ATP-stimulated I(sc) response, whereas it did not during the initial or recovered phases. ATP-induced increases of intracellular adenosine 3',5'- cyclic monophosphate showed similar desensitization and recovery in parallel with the changes in the responses of I(sc). The desensitization process was attenuated by pretreatment with cholera toxin or pertussis toxin. Taken together, our results suggest that the adenylyl cyclase system plays a role in the desensitization and recovery mechanism of the ATP-stimulated Cl^- secretion in MDCK cells.