Abstract
The uptake of 86Rb + was assayed in isolated rat pancreatic acinar cells to determine the effect of calcium and carbamoylcholine on the ouabain-sensitive and ouabain-insensitive components. The presence of calcium in the medium bathing the cells during the preincubation and the main incubation periods was needed to preserve in optimum conditions the uptake of 86Rb +, the stimulation by carbamoylcholine and the sensitivity to ouabain. In the presence of calcium, the ouabain-sensitive component of 86Rb + uptake was higher than the ouabain-insensitive. The ouabain-sensitive component was 3-times lower in cells incubated in a medium lacking calcium and containing 1 mM EGTA, as compared to cells incubated in the presence of calcium. Carbamoylcholine, at 5 · 10 −4 M, stimulated the uptake of 86Rb + and this effect depended on the presence of calcium in the bathing medium. Maximal stimulation by carbamoylcholine was reached at 0.2 mM calcium. The nett stimulation by carbamoylcholine was inhibited up to 85% by 1 mM ouabain. As judged by digitonin-disruption of plasma membrane, the above-indicated effects were limited to a cytoplasmic pool of 86Rb + and a leaky plasma membrane could be ruled out. The results suggest that in rat pancreatic acinar cells, carbamoylcholine stimulated the ouabain-sensitive uptake of 86Rb + and required the presence of calcium in the bathing medium.
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