CARBACHOL-INDUCED [CA2-MUSCLE CELLS OF GUINEA-PIG ILEUM(](I) OSCILLATIONS IN SINGLE SMOOTH)

1. Changes in cytosolic Ca2+ concentration ([Ca2+](i)) produced by car bachol (CCh) were measured in single smooth muscle cells of guinea-pig ileum using a Ca2+-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 mu m CCh, exhibited repeated changes i n [Ca2+](i) giving a serrated appearance. The oscillatory changes [Ca2 +](i) were very similar to those evoked by increasing extracellular K concentration ([K+](o)) to 30 nm, which were abolished by removal of extracellular Ca2+, nifedipine and La3+, but remained unchanged after depletion of internal Ca2+ store with cyclopiazonic acid, thapsigargin and ryanodine. 3. Every individual [Ca2+](i) oscillation was just lik e a [Ca2+](i) increase generated spontaneously in about 8% of cells of 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 m u m CCh, slower [Ca2+](i) oscillations were elicited and every individ ual [Ca2+](i) oscillation was always preceded by the fast brief increa se in [Ca2+](i). 5. [Ca2+](i) oscillations elicited by 2 mu m CCh were temporally and functionally distinct from those induced by high [K+]( o). They were more or less regular in the periodicity and pattern, com prised pacemaker potential-like [Ca2+](i) increases or sinusoidal type s of [Ca2+](i) increases, and could be elicited even in 100 mM K-o(+). 6. Removal of extracellular Ca2+ or application of nifedipine, methox yverapamil (D600), diltiazem or La3+ during CCh (2 mu m)-induced [Ca2](i) oscillations caused them to disappear. In cells in which internal Ca2+ stores were depleted, 2 mu m CCh did not evoke [Ca2+](i) oscilla tions but occasionally induced single or repeated generation of the in crease in [Ca2+](i) with a serrated appearance. 7. The results indicat e that CCh can induce two types of [Ca2+](i) oscillation in guinea-pig ileal smooth muscle cells; one arises from Ca2+ influx associated wit h action potential discharges and the other from periodic release of C a2+ from internal stores. The latter [Ca2+](i) oscillation requires ex tracellular Ca2+ to sustain it.