G protein-regulated large-conductance chloride channels in freshly isolated fetal type II alveolar epithelial cells.
Using the patch-clamp technique, we have recorded single channels in cell-attached and inside-out excised patches from the plasma membrane of type II alveolar epithelial cells freshly isolated from fetal guinea pig lung by elastase digestion and differential filtration. In cell-free patches the channels were highly selective for Cl- (PCl:Pcat = 9:1), had a large unitary conductance (375 pS +/- 23 pS), and current reversal of 0 mV in either symmetrical Na(+)-rich solutions or when the inner membrane leaflet was bathed in a K(+)-rich solution. The large-conductance Cl- channel exhibited little or no voltage inactivation at positive potentials, remained open for a significant amount of time at potentials negative to -40 mV, and was blocked at all potentials by 0.1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid. Channel activity was independent of intracellular calcium concentration. Bath addition of the nonmetabolizable analogue of GTP, GTP gamma S (0.1 mM), caused a voltage-dependent inhibition of channel activity [open probability (Po) plot was shifted by at least +25 mV]. Smaller channels (25 +/- 3 pS) were recorded in the cell-attached configuration with a current-voltage (I-V) relationship which was compatible with a Cl- conductance. On excision, the patches previously containing small-conductance channels exhibited only large-conductance Cl- channel behavior. These large-conductance, G protein-regulatable Cl- channels may provide a route for alveolar cell Cl- exit and as such may be an integral part of the mechanism responsible for secretion of fetal lung fluid.
Kemp
P J
PJ
Department of Child Health, Ninewells Hospital and Medical School, University of Dundee, United Kingdom.
MacGregor
G G
GG
Olver
R E
RE
D000818:Animals; D002469:Cell Separation; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D004553:Electric Conductivity; D004848:Epithelium / Q000196:embryology / Q000502:physiology; D005333:Fetus / Q000166:cytology / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006168:Guinea Pigs; D011650:Pulmonary Alveoli / Q000196:embryology / Q000502:physiology*; D013267:Stilbenes / Q000494:pharmacology
D018118:Chloride Channels; D013267:Stilbenes; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins