Effect of ATP, carbachol and other agonists on intracellular calcium activity and membrane voltage of pancreatic ducts.
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 Ca(2+)-sensitive probe fura-2. In some experiments we also measured the basolateral membrane voltage, Vbl, 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 mumol/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 Vbl 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 Vbl (n = 4). Several other putative agonists of pancreatic HCO3- secretion were also tested for their effects on [Ca2+]i.(ABSTRACT TRUNCATED AT 250 WORDS)
Hug
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Physiologisches Institut, Albert-Ludwigs-Universität, Freiburg, Germany.
Pahl
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C
Novak
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D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D002118:Calcium / Q000032:analysis* / Q000502:physiology; D015220:Calcium Channels / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology*; D002766:Cholecystokinin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D008839:Microelectrodes; D008856:Microscopy, Fluorescence; D009496:Neurotensin / Q000494:pharmacology; D010183:Pancreatic Ducts / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013373:Substance P / Q000494:pharmacology
D015220:Calcium Channels; D013373:Substance P; D009496:Neurotensin; D000255:Adenosine Triphosphate; D002217:Carbachol; D002766:Cholecystokinin; D001839:Bombesin; D002118:Calcium