Characterization of Muscarinic Receptors in Singl Smooth Muscle Cells

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Characteristics of muscarinic receptors in guinea pig visceral muscles and the single cells prepared by enzymatic digestion were investigated.Preparation of single smooth muscle cells : Enzymatic digestion of smooth muscle, with combination of highly purified collagenase and papain, yielded single cells which were responsive to various agonists.Determination of contractile responses of single muscle cells : A procedure for determination of contractile responses of single muscle cells was developed with use of a phase contrast microscope and a microcomputer.Mode of contractile response of single smooth muscle cells : The dispersed cells were contracted by carbachol dose-dependently, indicating that the mode of contraction was graded type. Each cell, however, had different sensitivity to agonists and the dose-response curves were different in each cell. Superimpose of those curves became resembled to that obtained with the intact tissue suggesting that force development of each cell in the tissue evoked contraction of the tissue. Characteristics of the muscarinic receptors in the single cells : Affinity to agonists in the isolated single cells were not altered during preparation of the cells by enzymatic digestions. With use of the single cells, it was revealed that the muscarinic receptors in the visceral muscle were consisted of three subtypes and each pKi was 7.1, 5.8 and 4.0.Role of phosphatidic acids in contraction of smooth muscle : Stimulating the muscarinic receptors, phospholipase C and diacylglycerol Kinase were activated, and content of intracellular phosphatidic acid was increased. The acid stimulated release of intracellular free calcium which induced muscle contraction.