Tension and cycb'c GMP changes in potassium depolarized rabbit colon muscle

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Abstract
Potassium depolarization of rabbit colon muscle elicited a contraction consisting of 2 distinct phases, an initial rapid phasic contraction and a tonic contracture. The tonic contraction was, in contrast to the phasic contraction, dependent on the extracellular calcium for its development. There was a correlation between the tension development and the increase of the cyclic GMP level in the K+‐depolarized muscle. Experimental conditions which abolished the tonic contracture,vizglucose omission and treatment with Ca2+‐antagonists (verapamil, SKF 525A) also inhibited the cyclic GMP response. The changes of the cyclic GMP levels were Ca2+‐dependent. K+‐ions also changed the cyclic AMP content an effect which was atropine sensitive. From the experimental data obtained in this investigation we suggest that the co‐variation of the tension and the cyclic GMP level in the depolarized colon muscle might depend on oscillations in a common intracellular factor, probably Ca2+.