Secretagogue effects on intracellular calcium in pancreatic duct cells

Abstract

Regulation of intracellular free calcium ([Ca²⁺]_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 Ca²⁺-sensitive, fluorescent probe Fura-2. Rat and guinea pig duct cells exhibited mean resting [Ca²⁺]_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 [Ca²⁺]_i involved both mobilization of Ca²⁺ from intracellular stores and stimulation of influx of extracellular Ca²⁺. In contrast, neither cholecystokinin nor secretin showed reproducible or sizeable increses in [Ca²⁺]_i. Both rat and guinea pig duct cells showed considerable resting Ca²⁺ permeability. Lowering or raising the extracellular [Ca²⁺]_i led, respectively, to a decrease or increase in the resting [Ca²⁺]_i. Application of Mn²⁺ resulted in a quenching of the fluorescence signal indicating its entry into the cell. The resting Ca²⁺ and Mn²⁺ permeability could be blocked by La³⁺ suggesting that it is mediated by a Ca²⁺ channel.