Inhibitory Effects of Caffeine on Developed Tension and Calcium Movement in Guinea Pig Taenia Coli in High-K Medium

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Abstract
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) 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. Caffeine had no effect on the developed tension of the glycerinated taenia induced by Ca, Mg and ATP. 14C-Caffeine entered the cell in the presence of high-K. Caffeine may inhibit high-K induced contracture by inhibiting Ca influx into the contractile mechanism.