Receptor Operated Intracellular Calcium Stores in the Smooth Muscle of the Guinea Pig Bladder

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Abstract
The in vitro behavior of strips of guinea pig bladder and tenia coli was studied. Both bladder and tenia temporarily retain their ability to contract in Ca-free solutions, but the magnitude of this response decays with time. Carbachol is capable of producing contraction in Ca-free solution for a longer period of time than K depolarization. Once lost, the ability of carbachol (but not K) to contract the tissues in Ca-free solution can be temporarily restored by a brief application of high Ca. The size of the carbachol contraction in Ca-free solution is reduced in Na-free solution, suggesting that membrane-bound Ca may not play a major role in this response. In depolarized bladder exposed to nifedipine 2 .times. 10-7 M, carbachol can only elicit 1 large concentration, suggesting depletion of an intracellular source. Whereas the response of the bladder to depolarization depends primarily on extracellular Ca, the response to carbachol may also involve release of stored Ca, and the bladder, like other smooth muscles, appears to contain agonist-releasable intracellular Ca stores.