title: Calcium secretion in the isolated perfused canine pancreas.
abstract: The quantitative relation of calcium and protein secretion was studied on the isolated perfused canine pancreas at different secretory states of hydrokinetic and ecbolic stimulation and various extracellular Ca++-concentrations. 1. Calcium and protein secretion are correlated at both ecbolic and hydrokinetic stimulation as well as by biological or synthetic secretion. 2. Enzyme-associated calcium was estimated at 35 nmol/mg protein and did not vary under differing stimulatory and secretory conditions. 3. During variable concentrations of synthetic secretin basal protein and calcium concentrations in the pancreatic juice show a hyperbolic relationship to the respective rates of fluid secretion. At flow rates beyond 3 ml/5 min the calcium concentrations asymptotically tend to 0.46 mEq/l while protein concentrations nearly decrease to zero. Moreover, the y-intercept of the regressionline correlating the calcium and protein concentrations gives with 0.48 mEq/l Ca++ additional evidence of the existence and magnitude of an enzyme-independent calcium fraction, which seems to remain constant over the whole range of secretory rates. 4. The omission of perfusate calcium does not abolish the calcium-protein correlation either at hydrokinetic or at ecbolic stimulation, but diminishes the enzyme-independent calcium fraction. 5. Enhancing perfusate Ca++-concentrations augments calcium output byt fails in stimulating enzyme secretion. It is concluded that at exclusively hydrokinetic stimulation basal secreted protein with a definite amount of chelated calcium is diluted by variable rates of pancreatic juice containing enzyme independent Ca++ at a constant concentration. During different secretory states of hydrokinetic or ecbolic stimulation the respective proportions of enzyme associated and independent calcium vary, and thus determine changes in the calcium-protein ratios. Extracellular calcium can only influence the non-protein-bound calcium fraction of the pancreatic juice presumably by diffusion from the extracellular fluid through the ductal epithelium rather than by an active secretory mechanism.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D004285:Dogs; D066298:In Vitro Techniques; D007700:Kinetics; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism*; D010189:Pancreatic Juice / Q000187:drug effects / Q000378:metabolism; D010477:Perfusion / Q000295:instrumentation; D012633:Secretin / Q000494:pharmacology; D012636:Secretory Rate / Q000187:drug effects
chemical_list: D002135:Calcium-Binding Proteins; D012633:Secretin; D002118:Calcium