Carbachol-induced [Ca2+]i oscillations in single smooth muscle cells of guinea-pig ileum.
1. Changes in cytosolic Ca2+ concentration ([Ca2+]i) produced by carbachol (CCh) were measured in single smooth muscle cells of guinea-pig ileum using a Ca(2+)-sensitive fluorescent dye, fura-2, to clarify the underlying mechanisms of muscarinic [Ca2+]i oscillations. 2. Half of the cells, when exposed to 0.2 microM CCh, exhibited repeated changes in [Ca2+]i giving a serrated appearance. The oscillatory changes in [Ca2+]i were very similar to those evoked by increasing extracellular K(+) concentration ([K+]o) to 30 mM, which were abolished by removal of extracellular Ca2+, nifedipine and La3+, but remained unchanged after depletion of internal Ca2+ stores with cyclopiazonic acid, thapsigargin and ryanodine. 3. Every individual [Ca2+]i oscillation was just like a [Ca2+]i increase generated spontaneously in about 8% of cells or triggered by an action potential evoked by a current pulse in current-clamped cells. 4. In the remaining half of the cells exposed to 0.2 microM CCh, slower [Ca2+]i oscillations were elicited and every individual [Ca2+]i oscillation was always preceded by the fast brief increase in [Ca2+]i. 5. [Ca2+]i oscillations elicited by 2 microM CCh were temporally and functionally distinct from those induced by high [K+]o. They were more or less regular in the periodicity and pattern, comprised pacemaker potential-like [Ca2+]i increases or sinusoidal types of [Ca2+]i increases, and could be elicited even in 100 mM K+(o). 6. Removal of extracellular Ca2+ or application of nifedipine, methoxyverapamil (D600), diltiazem or La3+ during CCh (2 micro M)-induced [Ca2+]i oscillations caused them to disappear. In cells i which internal Ca2+ stores were depleted, 2 microM CCh did not evoke [Ca2+]i oscillations but occasionally induced single or repeated generation of the increase in [Ca2+]i with a serrated appearance. 7. The results indicate that CCh can induce two types of [Ca2+]i oscillation in guinea-pig ileal smooth muscle cells; one arises from Ca2+ influx associated with action potential discharges and the other from periodic release of Ca2+ from internal stores. The latter [Ca2+]i oscillation requires extracellular Ca2+ to sustain it.
Kohda
M
M
Laboratory of Pharmacology, Department of Veterinary Science, Gifu University, Gifu, Japan.
Komori
S
S
Unno
T
T
Ohashi
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism*; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism; D006168:Guinea Pigs; D007082:Ileum / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology*; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D009991:Oscillometry; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism
D002121:Calcium Channel Blockers; D018721:Muscarinic Agonists; D002217:Carbachol; D011188:Potassium; D002118:Calcium