Regulation of cAMP-sensitive colonic epithelial Na+ channel in oocyte expression system.
J Comp Physiol B 2001;
171:369-75. [PMID:
11497124 DOI:
10.1007/s003600100185]
[Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In amphibian epithelia and in cortical collecting duct the antidiuretic peptide arginine-vasopressin (AVP) stimulates activity of epithelial Na+ channels (ENaCs). Generally, the AVP action upon Na+ (re)absorption is believed to be a cAMP/protein-kinase-A mediated mechanism. In the Xenopus oocyte expression system, however, a clear stimulation of ENaC activity by cAMP could not be reproduced with channel subunits cloned from A6 cells or rat colon. We have recently shown that membrane-permeant 8-(4-chlorophenylthio)-cAMP (cpt-cAMP) stimulates activity of a hybrid ENaC in Xenopus oocytes, that consists of an alpha-subunit cloned from guinea-pig colon and the beta- and gamma-subunit originating from rat colon (gpalpharbetagammaENaC). In the present study, we have further investigated the mechanisms by which cpt-cAMP upregulates gpalpharbetagammaENaC activity. Interestingly, we found AVP to stimulate the gpalpharbetagammaENaC in oocytes. Also, treatment with GTP-gamma-S largely activated this channel. In contrast, as a conflicting result, forskolin had no stimulatory effect on the cAMP-sensitive gpalpharbetagammaENaC. Experiments with Brefeldin A (BFA) or nocodazole suggested that only a minor part of cpt-cAMP-induced activation is probably due to an additional translocation of channel proteins into the oocyte membrane. In conclusion, the stimulatory effect of synthetic cpt-cAMP does not seem to be exclusively provided by classical cAMP/PKA-associated transduction mechanisms, i.e., as in A6 cells.
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