Abstract
Since the correlation between the K-induced contracture and the Ca movement during the contracture in guinea-pig taenia coli has been clarified, the effects of caffeine were deemed worthy of investigation. The tonic contraction induced by 40 mM K disappeared within 5 min in the presence of caffeine above 7 mM. The inhibitory effect of caffeine was reversed by a high concentration of Ca added to the external medium. High-K added to the medium increased tissue Ca, Ca uptake and the size of cellular Ca fraction that did not exchange within 4 min (tightly bound fraction, TBF), and it decreased Ca efflux. An application of 7 mM caffeine to the muscle treated with high-K for 30 min restored all parameters to the control level. Further, caffeine had no effect on the developed tension of the glycerinated taenia induced by Ca, Mg and ATP. It was observed that 14C-caffeme entered the cell in the presence of high-K. From these data, it is suggested that caffeine inhibits high-K induced contracture by inhibiting Ca influx into the contractile mechanism.
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