Secretagogue effects on intracellular calcium in pancreatic duct cells

Abstract

Regulation of intracellular free calcium ([Ca 2+ ] i ) in single epithelial duct cells of isolated rat and guinea pig pancreatic interlobular ducts by secretin, carbachol and cholecystokinin was studied by microspectrofluorometry using the Ca 2+ -sensitive, fluorescent probe Fura-2. Rat and guinea pig duct cells exhibited mean resting [Ca 2+ ] i of 84 nM and 61 nM, respectively, which increased by 50%–100% in response to carbachol stimulation, thus demonstrating the presence of physiologically responsive cholinergic receptors in pancreatic ducts of both species. The carbachol-induced increase in [Ca 2+ ] i involved both mobilization of Ca 2+ from intracellular stores and stimulation of influx of extracellular Ca 2+ . In contrast, neither cholecystokinin nor secretin showed reproducible or sizeable increses in [Ca 2+ ] i . Both rat and guinea pig duct cells showed considerable resting Ca 2+ permeability. Lowering or raising the extracellular [Ca 2+ ] i led, respectively, to a decrease or increase in the resting [Ca 2+ ] i . Application of Mn 2+ resulted in a quenching of the fluorescence signal indicating its entry into the cell. The resting Ca 2+ and Mn 2+ permeability could be blocked by La 3+ suggesting that it is mediated by a Ca 2+ channel.