Regulation of cAMP-sensitive colonic epithelial Na+ channel in oocyte expression system.
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.
Schnizler
M
M
Institut für Tierphysiologie der Justus-Liebig-Universität Giessen, Germany.
Schaffert
S
S
Clauss
W
W
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001127:Arginine Vasopressin / Q000494:pharmacology; D020126:Brefeldin A / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D004232:Diuretics / Q000494:pharmacology; D053503:Epithelial Sodium Channels; D019204:GTP-Binding Proteins / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D006168:Guinea Pigs; D007413:Intestinal Mucosa / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D015739:Nocodazole / Q000494:pharmacology; D009865:Oocytes / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014982:Xenopus laevis
D000970:Antineoplastic Agents; D004232:Diuretics; D053503:Epithelial Sodium Channels; D011500:Protein Synthesis Inhibitors; D015222:Sodium Channels; D014662:Vasoconstrictor Agents; D001127:Arginine Vasopressin; D005576:Colforsin; D020126:Brefeldin A; D000584:Amiloride; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D015739:Nocodazole