Increased uptake and efflux of calcium with acetylcholine stimulation in smooth muscle of toad stomach.

Abstract

SummaryThe effect of acetylcholine stimulation on Ca movements in depolarized smooth muscle from toad stomach muscle was investigated.No difference in the content of Ca45 due to ACh stimulation could be detected in muscle containing its full complement of Ca. However, in Ca depleted muscle exposed to Ca 0·05 mM, solution, uptake of Ca was accelerated and the equilibrium content of total and exchangeable Ca was increased by some 5% of the total tissue Ca. This amount was similar to the extra Ca lost when muscle was depleted into Ca‐free solution with intermittent ACh stimulation.The efflux of Ca45 from normal and replcted muscle was studied, using a constant flow system. ACh stimulation of both normal and repleted muscle resulted in a transient increase in the efflux of Ca45. The slow component of the efflux curve occupied a larger proportion of the cellular Ca in the repleted than in the normal muscle. The increment of Ca uptake due to ACh stimulation during repletion was found to be wholly in this fraction.The significance of these results in relation to an excitation‐contraction‐coupling fraction are discussed.