Abstract
The pancreatic duct has been regarded as a typical cAMP-regulated epithelium, and our knowledge about its Ca2+ homeostasis is limited. Hence, we studied the regulation of intracellular calcium, [Ca2+]i, in perfused rat pancreatic ducts using the Ca2+-sensitive probe fura-2. In some experiments we also measured the basolateral membrane voltage, V bl, of individual cells. The resting basal [Ca2+]i was relatively high, corresponding to 263±28 nmol/l, and it decreased rapidly to 106±28 nmol/l after removal of Ca2+ from the bathing medium (n=31). Carbachol increased [Ca2+]i in a concentration-dependent manner. At 10 μmol/l the fura-2 fluorescence ratio increased by 0.49±0.06 (n=24), corresponding to an increase in [Ca2+]i by 111±15 nmol/l (n=17). ATP, added to the basolateral side at 0.1 mmol/l and 1 mmol/l, increased the fluorescence ratio by 0.67±0.06 and 1.01±14 (n=46; 12), corresponding to a [Ca2+]i increase of 136±22 nmol/l and 294±73 nmol/l respectively (n= 15; 10). Microelectrode measurements showed that ATP (0.1 mmol/l) hyperpolarized V bl from −62±3 mV to-70±3 mV, an effect which was in some cases only transient (n=7). This effect of ATP was different from that of carbachol, which depolarized Vbl. Applied together with secretin, ATP delayed the secretin-induced depolarization and prolonged the initial hyperpolarization of V bl (n=4). Several other putative agonists of pancreatic HCO −3 secretion were also tested for their effects on [Ca2+]i. Bombesin (10 nmol/l) increased the fura-2 fluorescence ratio by 0.24±0.04 (n=8), neurotensin (10 nmol/l) by 0.25±0.04 (n=6), substance P (0.1 μmol/l) by 0.22±0.06 (n=6), and cholecystokinin (10 nmol/l) by 0.14±0.03 (n=7). Taken together, our studies show that Ca2+ homeostasis plays a role in pancreatic ducts. The most important finding is that carbachol and ATP markedly increase [Ca2+]i, but their different electrophysiological responses indicate that intracellular signalling pathways may differ.
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Hug, M., Pahl, C. & Novak, I. Effect of ATP, carbachol and other agonists on intracellular calcium activity and membrane voltage of pancreatic ducts. Pflugers Arch. 426, 412–418 (1994). https://doi.org/10.1007/BF00388304
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DOI: https://doi.org/10.1007/BF00388304