Caffeine and KC1 contracture in cat myocardium.

Caffeine increases the force of contracture induced in cat myocardium by exposure to 140 mM KC1 in isotonic Tyrode solution. The effect of caffeine does not require prior exposure to the drug, develops rapidly, and is partially antagonized by procaine but not by verapamil. These results suggest that caffeine acts on depolarized sarcolemma to release a sarcolemmal calcium pool.