Modulation of carbachol-induced [Ca2+]i oscillations by Ca2+ influx in single intestinal smooth muscle cells.
1. Oscillations of cytosolic Ca2+ concentration ([Ca2+]i) evoked by carbachol (CCh; 2 microM), a muscarinic agonist, were detected as oscillatory changes of muscarinic receptor-coupled cationic current (Icat) in guinea-pig ileal smooth muscle cells by the whole cell patch-clamp technique. 2. Reduction of extracellular Ca2+ from 2 mM to 0.2 or 0.05 mM, during CCh-induced Icat oscillations, caused them to disappear or to decrease markedly in frequency. A return to 2 mM Ca2+ concentration restored the initial Icat oscillations. 3. Application of nifedipine (1-3 microM) or D600 (2-5 microM) to block the voltage-gated Ca2+ channel (VGCC) decreased the frequency of the ongoing Icat oscillations in the cells held at -20 mV, but it was without effect in cells held at -60 mV. 4. Displacement of the holding potential of -20 mV to -60 mV to deactivate VGCC produced a decrease, an increase or no noticeable change in the frequency of the Icat oscillations in different cells. Displacement to 20 mV to inactivate VGCC invariably produced a decrease in the frequency. In nifedipine-treated cells, the Icat oscillations varied in frequency voltage-dependently in a reverse and linear way within the range -80 to 40 mV. 5. Application of thapsigargin (1 or 2 microM), an inhibitor of Ca(2+)-ATPase in the membrane of internal Ca2+ stores, caused CCh-induced Icat oscillations to disappear with a progressing phase during which their amplitude, but not frequency, declined. 6. The results suggest that membrane Ca2+ entry has a crucial role to play in regulation of the frequency of CCh-induced [Ca2+]i oscillations in addition to persistence of their generation, and that the effect is brought about by a potential mechanism independent of Ca2+ store replenishment. They also provide evidence that two types of Ca2+ permeant channels, VGCC and an as yet unidentified channel, are involved in the Ca2+ entry responsible for modulation of [Ca2+]i oscillations.
Komori
S
S
Department of Veterinary Science, Faculty of Agriculture, Gifu University, Japan.
Iwata
M
M
Unno
T
T
Ohashi
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018721:Muscarinic Agonists / Q000494:pharmacology*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D018721:Muscarinic Agonists; D019284:Thapsigargin; D002217:Carbachol; D002118:Calcium