Camp stimulates cftr-like cl- channels and inhibits amiloride -sensitive na+ channels in mouse ccd cells. Letz, Bernd, and Christoph Korbmacher. Zentrum der Physiologie, Klinikum der Johann Wolfgang Goethe -Universit[umlaut]at, D-60590 Frankfurt am Main, Germany
APStracts 3:0318C, 1996.
Confluent M-1 mouse cortical collecting duct (CCD) cells express highly selective low conductance amiloride-sensitive Na+ channels (Letz et al., J. Membrane 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 [mu]M) reduced the hyperpolarization in response to amiloride (10 [mu]M) 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- solution 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 CFTR-like Cl- channels. IBMX (3-isobutyl-1 -methylxanthine) and cpt-cAMP (chlorophenylthio-cAMP) mimicked the effects of forskolin, while 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 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. 

Received 18 July 1996; accepted in final form 23 September 1996.
APS Manuscript Number C399-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996