THE RELATIONSHIP BETWEEN THE CALCIUM CONTENT OF DEPOLARIZED MAMMALIAN SMOOTH MUSCLE AND ITS CONTRACTILITY IN RESPONSE TO ACETYLCHOLINE

Abstract

Summary Only a small fraction of the calcium content of depolarized cat circular intestinal smooth muscle is necessary for muscle contraction in response to acetylcholine stimulation at 25°. Equilibration of the tissue at 37° in calcium containing sodium chloride Ringer and potassium sulphate Ringer for up to 6 hr. did not significantly alter the calcium content of 1·57 μmoles/g. Magnesium, sodium and potassium contents were measured concurrently. Tissue damage increased the calcium content by 26%. Storage at 6° resulted in calcium contents of 123%, 180% and 294% after 24 hr., 48 hr. and 120 hr. respectively. The tissue still spontaneously contracted after re‐equilibration at 36°. Equilibration of the smooth muscle in calcinm containing potassium sulphate Ringer at 25° likewise did not significantly alter the calcium content of the tissue. Contractile responses to maximal acetylcholine stimulation were lost in calcium free potassium sulphate Ringer at 25° when 22% of the tissue calcium remained. Replacement of only a further 9% giving a total calcium content of 31% fully restored contractility.