A B S T R A C T In dispersed acinar cells prepared from guinea pig pancreas, cellular uptake of 4... more A B S T R A C T In dispersed acinar cells prepared from guinea pig pancreas, cellular uptake of 45Ca was moderately rapid and reached a steady state bv 60 min. At the steady state, 69% of total cellular 45Ca was membrane-bound. In acinar cells preloaded with 45Ca and then incubated with COOH-terminal octapeptide of cholecystokinin (CCK-OP) or carbanylcholine, total cellular 45Ca decreased by approximately 40% within 5-10 min and then steadily increased to control values by 60 min. Under identical conditions, membranebound 45Ca decreased by 40% within 5-10 min and remained constant for the duration of the incubation. Free cellular 45Ca did not change during the initial 30 min but then increased steadily to values three times those in control cells by 60 min. In cells preloaded with 45Ca and then incubated with EDTA, the loss of total cellular radioactivitv stimulated b)y CCK-OP could be accounted for by loss of membrane-bound 45Ca. CCK-OP failed to alter total cellular uptake of 45Ca when both tracer and peptide were added at the beginning of the incubation. Under identical conditions, membrane-bound 45Ca was not altered b1 CCK-OP during the first 30 min of incubation but was significantly below control values after this time. The effect of CCK-OP on free cellular 45Ca was the same as in cells preloaded with the tracer. These results suggest that CCK-OP catuses release of 45Ca from a membrane-botund compartment that equilibrates slowly with extracellular fluid and that the change in free cellular 45Ca is a secondary effect. NIETHODS Male Hartley strain albino guinea pigs (350-400 g) were obtained from the Small Animals Section, Veterinary Resources Branch, National Institutes of Health, Bethesda, md. 45Ca (12.5 mCi/mg) and ["sC]alpha-aminoisobutyric acid (AIB,' 5.1 mCi/mmol) were purchased from New England Nuclear (Boston, Mass.); 42K (2.6 mCi/mg) from ICN Corp., Irvine, Calif.); crude collagenase (Clostridium histolyticu mz, 'Abbreviations tised in this paper: AIB, alpha-aminoisobutyric acid; CCK-OP, COOH-terminial octapeptide of cholecvstokinin.
A B S T R A C T In dispersed acinar cells prepared from guinea pig pancreas, cellular uptake of 4... more A B S T R A C T In dispersed acinar cells prepared from guinea pig pancreas, cellular uptake of 45Ca was moderately rapid and reached a steady state bv 60 min. At the steady state, 69% of total cellular 45Ca was membrane-bound. In acinar cells preloaded with 45Ca and then incubated with COOH-terminal octapeptide of cholecystokinin (CCK-OP) or carbanylcholine, total cellular 45Ca decreased by approximately 40% within 5-10 min and then steadily increased to control values by 60 min. Under identical conditions, membranebound 45Ca decreased by 40% within 5-10 min and remained constant for the duration of the incubation. Free cellular 45Ca did not change during the initial 30 min but then increased steadily to values three times those in control cells by 60 min. In cells preloaded with 45Ca and then incubated with EDTA, the loss of total cellular radioactivitv stimulated b)y CCK-OP could be accounted for by loss of membrane-bound 45Ca. CCK-OP failed to alter total cellular uptake of 45Ca when both tracer and peptide were added at the beginning of the incubation. Under identical conditions, membrane-bound 45Ca was not altered b1 CCK-OP during the first 30 min of incubation but was significantly below control values after this time. The effect of CCK-OP on free cellular 45Ca was the same as in cells preloaded with the tracer. These results suggest that CCK-OP catuses release of 45Ca from a membrane-botund compartment that equilibrates slowly with extracellular fluid and that the change in free cellular 45Ca is a secondary effect. NIETHODS Male Hartley strain albino guinea pigs (350-400 g) were obtained from the Small Animals Section, Veterinary Resources Branch, National Institutes of Health, Bethesda, md. 45Ca (12.5 mCi/mg) and ["sC]alpha-aminoisobutyric acid (AIB,' 5.1 mCi/mmol) were purchased from New England Nuclear (Boston, Mass.); 42K (2.6 mCi/mg) from ICN Corp., Irvine, Calif.); crude collagenase (Clostridium histolyticu mz, 'Abbreviations tised in this paper: AIB, alpha-aminoisobutyric acid; CCK-OP, COOH-terminial octapeptide of cholecvstokinin.
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