cAMP stimulates CFTR-like Cl- channels and inhibits amiloride-sensitive Na+ channels in mouse CCD cells.
Confluent M-1 mouse cortical collecting duct (CCD) cells express highly selective low-conductance amiloride-sensitive Na+ channels (B. Letz, A. Ackermann, C. M. Canessa, B. C. Rossier, and C. Korbmacher, J. Membr. Biol. 148: 129-143, 1995). Here we investigated the effect of forskolin on membrane voltage and whole cell currents of confluent M-1 cells using the patch-clamp technique. Forskolin (1 microM) reduced the hyperpolarization in response to amiloride (10 microM) from 17 to 4 mV and decreased the amiloride-sensitive Na+ inward currents from 81 to 26 pA. Furthermore, forskolin increased the hyperpolarization caused by changing from an apical low-Cl- solution (9 mM) to a high-Cl- solution (149 mM) from 11 to 30 mV and increased the magnitude of the inward current changes induced by alternating between high-Cl- and low-Cl- solutions from 25 to 138 pA. This demonstrates that forskolin stimulates an apical Cl- conductance. Anion substitution experiments revealed a permeability sequence SCN- > Br- > Cl- > I- >> gluconate. This suggests that the stimulated channels are cystic fibrosis transmembrane conductance regulator (CFTR)-like Cl- channels. 3-Isobutyl-1-methylxanthine and 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate mimicked the effects of forskolin, whereas 1,9-dideoxyforskolin had no effect. We conclude that, in addition to amiloride-sensitive Na+ channels, CFTR-like Cl- channels are present in the apical membrane of confluent M-1 cells. An increase in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) activates these Cl- channels and concurrently reduces the activity of the Na+ channels. This reciprocal regulation by cAMP suggests that the channels are functionally coupled.
Letz
B
B
Zentrum der Physiologie, Klinikum der Johann Wolfgang Goethe-Universität, Frankfurt am Main, Germany.
Korbmacher
C
C
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels / Q000378:metabolism*; D002712:Chlorides / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D004553:Electric Conductivity; D004594:Electrophysiology; D007672:Kidney Cortex; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D018408:Patch-Clamp Techniques; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000187:drug effects*
D018118:Chloride Channels; D002712:Chlorides; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D000584:Amiloride; D000242:Cyclic AMP