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 th e P-2 receptor-mediated stimulation of Cl- secretion in Madin-Darby ca nine kidney (MDCK) cell monolayers by assaying the response of short-c ircuit current (I-sc). When the cells were exposed to repeated 3-min c hallenges of ATP or UTP interspersed with 5-min washes, the response o f I-sc desensitized rapidly followed by spontaneous recovery. The patt ern of inhibition by various channel blockers or enzyme inhibitors rev ealed that both the initial and recovered responses of I-sc have the s ame ionic and signaling mechanisms. The desensitization and recovery p rocesses were confined to the membrane exposed to the repeated challen ges. When added during the desensitized phase, 8-bromoadenosine 3',5'- cyclic monophosphate enhanced the ATP-stimulated I-sc response, wherea s it did not during the initial or recovered phases. ATP-induced incre ases of intracellular adenosine 3',5'-cyclic monophosphate showed simi lar desensitization and recovery in parallel with the changes in the r esponses of I-sc. The desensitization process was attenuated by pretre atment with cholera toxin or pertussis toxin. Taken together, our resu lts suggest that the adenylyl cyclase system plays a role in the desen sitization and recovery mechanism of the ATP-stimulated Cl- secretion in MDCK cells.