Interaction of Acetylcholine Calcium and Depolarization in the Contraction of Smooth Muscle

Journal/Book: (Reprinted from Nuture Vol 190 No. 4773 pp. 350-352 April 22 1961). 1961;

Abstract: Department of Pharmacology University College London W.C.1. SMOOTH muscle which has been depolarized by external application of potassium still contracts in response to acetylcholine. This response reqoires calcium (ref. 2 and personal communication from D. H. Jenkinson). Calcium ions alone cause the depolarized smooth muscle to contract. If an isolated rat uterus is immersed at room temperature in calciumfree isotonic potassium sulphate-Ringer (22·0 gm. K2S04 0·36 gm. KHCO3 1·0 gm. glucose/litre) it contracts briefly and then relaxes completely. At this stage the application of very low concentrations of calcium (0·1 mM) causes the development of a reversible tension. The magnitude of the tension increases with concentration of calcium up to about 1·2 mM. Higher concentrations of calcium produce diminishing responses in tension. The maximum tensions developed by calcium are less than the maximum of which the preparation is capable and they can be increased by acetylcholine. The effect of 10-5 acetylcholine added to 2·4 mM calcium is shown in Fig 1 . . .

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