The effects of phospholipase C on excitation-contraction coupling mechanisms in smooth muscle

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Abstract
The technique of incubation with phospholipase C has been used as a means of investigating the role of phospholipids in the excitation-contraction coupling mechanisms of smooth muscle. The effects of this incubation procedure were observed upon the interactions of calcium with the contractile responses of the guinea-pig ileum longitudinal muscle preparation under a number of conditions. The reduction in the acetylcholine responses of both normal and potassium depolarized tissues after incubation was partially restored by a tenfold increase in the calcium concentration of the bathing medium. A faster rate of decline of contractile responses upon immersion in calcium-free solutions and a slower rate of restoration upon the reintroduction of calcium were seen in both normal and depolarized tissues. The relation between the external calcium concentration and the size of the contractile responses to a given stimulus was also changed. The size of the response to added calcium obtained in a potassium depolarized preparation was also reduced after phospholipase C incubation. These results and their implications are discussed.