Octanoate increases cytosolic Ca2+ concentration and membrane conductance in ovine pancreatic acinar cells |
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Authors: | K Katoh M Ohbo M Wakui |
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Institution: | (1) Department of Animal Physiology, Tohoku University, Faculty of Agriculture, Aoba-ku, Sendai, 981, Japan, Tel.: +81-22/717-8700, Fax: +81-22/717-8701, e-mail: kato@bios.tohoku.ac.jp, JP;(2) Department of Physiology, Medical School, Hirosaki University, Hirosaki, 036 Japan, JP |
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Abstract: | In order to investigate the cellular mechanisms involved in amylase release in response to stimulation with short-chain fatty
acids, changes in intracellular calcium concentration (Ca2+]i), membrane current and amylase release were measured in pancreatic acinar cells of sheep. Both octanoate and acetylcholine
raised Ca2+]i in acinar cells in a concentration-dependent manner. The rise in Ca2+]i in response to the stimulation with octanoate (10 mmol ⋅ l-1) was reduced in a medium without CaCl2, but was markedly enhanced by reintroduction of CaCl2 into the medium up to 2.56 mmol ⋅ l-1. Perfusion of the cells with a medium containing octanoate (5 mmol ⋅ l-1) or acetylcholine (0.5 μmol ⋅ l-1) immediately raised inward current across the cell membrane at a holding-membrane potential of −30 mV. The inward current
became greater as the holding potential became more negative. The equilibrium potential was 1.8 mV and 3.9 mV for octanoate
and acetylcholine, respectively, being consistent with that for Cl-. Although intracellular application of octanoate through a patch-clamp pipette also raised inward current after several minutes
in some cells (4 out of 12), this possibility was significantly smaller than that for extracellular application. In other
cells, even though the intracellular application of octanoate did not cause an increase in current, it always caused responses
immediately after introduction of the fatty acid into the medium. Stimulation with fatty acid as well as acetylcholine raised
amylase release in a concentration-dependent manner in cells dispersed from tissue segments with crude collagenase and trypsin
inhibitor. Without trypsin inhibitor, crude collagenase significantly and selectively reduced the octanoate (10 mmol ⋅ l-1)-induced amylase release. Dispersion with crude collagenase and trypsin significantly reduced both responses induced by octanoate
and acetylcholine (5.5 μmol ⋅ l-1). We conclude that fatty acids and acetylcholine increase Ca2+]i, which consequently evokes a rise in transmembrane ion (Cl-) conductance and amylase release, and that trypsin-sensitive protein(s) in the cell membrane are involved in secretory processes
activated by stimulation with fatty acids in ovine pancreatic acinar cells.
Accepted: 14 May 1996 |
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Keywords: | Short-chain fatty acids Exocrinepancreas Acinar cells Cytosolic calcium |
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