Regulation of cAMP-sensitive colonic epithelial Na+ channel in oocyte expression system

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Vol. 171; no. 5; pp. 369 - 375
• Main Authors: Schnizler, M, Schaffert, S, Clauss, W
• Format: Journal Article
• Language: English
• Published: Germany 01.06.2001
• Subjects: Amiloride - pharmacology; Animals; Antineoplastic Agents - pharmacology; Arginine Vasopressin - pharmacology; Brefeldin A - pharmacology; Colforsin - pharmacology; Colon - metabolism; Cyclic AMP - metabolism; Cytoskeleton - metabolism; Diuretics - pharmacology; Epithelial Sodium Channels; Gene Expression - physiology; GTP-Binding Proteins - metabolism; Guinea Pigs; Intestinal Mucosa - metabolism; Membrane Potentials - drug effects; Membrane Potentials - physiology; Nocodazole - pharmacology; Oocytes - physiology; Patch-Clamp Techniques; Protein Synthesis Inhibitors - pharmacology; Rats; Sodium Channels - genetics; Sodium Channels - metabolism; Vasoconstrictor Agents - pharmacology; Xenopus laevis
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/s003600100185

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.