We studied the mechanisms and characteristics of the spontaneously evoked intracellular Ca
2+ changes(Ca
2+ oscillations)in ileal longitudinal smooth muscle from guinea pig.Two-dimensional images of Ca
2+ oscillations were obtained at 33-ms intervals with a Ca
2+-sensitive fluorescence probe, fluo-3 using the intensified CCD camera.Nicardipine(10
-7M)significantly decreased the maximum level of fluorescence intensity of the Ca
2+ oscillations, inhibited the frequency of the oscillations and tended to decrease the basal level of fluorescence intensity.However, tetrodotoxin(3×10
-7M)did not affect these oscillations.Phorbol 12, 13-dibutyrate(10
-7M)significantly increased the maximum level of fluorescence intensity and the frequency of Ca
2+ oscillations, and it changed them to steady and chronometric Ca
2+ oscillations.Cyclopiazonic acid(3×10
-5M)also significantly increased the frequency of Ca
2+ oscillations.Acetylcholine(10
-8M)increased the basal and maximum level of fluorescence intensity and the frequency of Ca
2+ oscillations, and accelerated their onset.The increase of basal level of fluorescence intensity was then decreased by cyclopiazonic acid treatment.These results suggest that the augmentation of Ca
2+ oscillations is mainly due to the activation of L-type Ca
2+ channels, which is modulated by protein kinase C, and that the emptying of intracellular Ca
2+ stores may activate the Ca
2+ oscillations mediated through the increase of Ca
2+ influx in ileal smooth muscle of guinea pig.
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