Oscillations of receptor-operated cationic current and internal calcium in single guinea-pig ileal smooth muscle cells.
In single cells isolated from guinea-pig ileal smooth muscle, held under voltage clamp at -40 mV or -50 mV by patch pipette in the whole-cell recording mode, carbachol (CCh) evoked an oscillatory inward cationic current. The frequency of current oscillations increased with increasing CCh concentration. CCh-evoked current oscillations were followed very closely by oscillations in intracellular free Ca2+ estimated from the Indo-1 signal, and were abolished by inclusion of EGTA in the pipette solution. Ryanodine and heparin, but not nifedipine, blocked the generation of current oscillations. CCh-evoked current oscillations were abolished upon withdrawal of extracellular calcium and restored upon its reintroduction. Inclusion of GTP[gamma S] in the pipette solution caused the generation of an oscillatory inward current, which was blocked by ryanodine. The present results are consistent with the hypothesis that CCh-evoked cationic current is gated by activation of a G protein and is steeply dependent on [Ca2+]i, fluctuations in the release of Ca2+ from stores during carbachol's action produce oscillations in [Ca2+]i which cause similar oscillations in the cationic current.
Komori
S
S
Department of Veterinary Medicine, Gifu University, Japan.
Kawai
M
M
Pacaud
P
P
Ohashi
H
H
Bolton
T B
TB
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006168:Guinea Pigs; D006493:Heparin / Q000494:pharmacology; D007082:Ileum / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology; D015398:Signal Transduction
D011956:Receptors, Cell Surface; D012433:Ryanodine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D002217:Carbachol; D006493:Heparin; D009543:Nifedipine; D002118:Calcium