G proteins mediate suppression of Ca2+-activated K current by acetylcholine in smooth muscle cells.
The role of G proteins in cholinergic suppression of Ca2+-activated K current was studied in isolated canine colonic myocytes with the whole cell voltage-clamp technique. Acetylcholine (ACh; 10.0 microM) caused a 64 +/- 2.4% depression in the Ca2+-dependent component of the outward current evoked at potentials between -45 and -15 mV when GTP (0.1 microM) was included in the pipette-filling solution. This effect was reversed within 2-4 min on washout of ACh. Without GTP in the filling solution, ACh caused a 15 +/- 2.5% depression in outward current in 60% of the cells tested. When the non-hydrolyzable GTP analogues, GTP gamma S (0.1 mM) or 5'-guanylylimidodiphosphate (GppNHp; 0.1 mM) were used, the decrease in outward current was greater (85 +/- 4.2 and 78 +/- 6.5%, respectively), and it was not reversed on withdrawal of ACh. Dialysis of the cell interior with pipette solution containing pertussis toxin (1 ng/ml) for 30 min had no effect on the whole cell currents evoked on depolarization, but it abolished the effect of ACh on Ca2+-dependent outward current. These data suggest that coupling of muscarinic receptors to the inhibition of Ca2+-activated K channels is mediated by pertussis toxin-sensitive G proteins in colonic smooth muscle cells. G protein-mediated inhibition is distinctly different from the opening of muscarinic-regulated K channels in other cell types.
Cole
W C
WC
Department of Physiology, University of Nevada School of Medicine, Reno 89557.
Sanders
K M
KM
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003106:Colon / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D004285:Dogs; D004553:Electric Conductivity; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009116:Muscarine / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D037342:Pertussis Toxin; D011188:Potassium / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000378:metabolism / Q000494:pharmacology
D010566:Virulence Factors, Bordetella; D006165:Guanylyl Imidodiphosphate; D009116:Muscarine; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium