Endoplasmic reticulum Ca2+ store: regulation of Ca2+ release and reuptake by intracellular and extracellular Ca2+ in pancreatic acinar cells.
We investigated the effect of cytosolic and extracellular Ca2+ on Ca2+ signals in pancreatic acinar cells by measuring Ca2+ concentration in the cytosol([Ca2+]c) and in the lumen of the ER([Ca2+]Lu). To control buffers and dye in the cytosol, a patch-clamp microelectrode was employed. Acetylcholine released Ca2+ mainly from the basolateral ER-rich part of the cell. The rate of Ca2+ release from the ER was highly sensitive to the buffering of [Ca2+]c whereas ER Ca2+ refilling was enhanced by supplying free Ca2+ to the cytosol with [Ca2+]c clamped at resting levels with a patch pipette containing 10 mM BAPTA and 2 mM Ca2+. Elevation of extracellular Ca2+ to 10 mM from 1 mM raised resting [Ca2+]c slightly and often generated [Ca2+]c oscillations in single or clustered cells. Although pancreatic acinar cells are reported to have extracellular Ca2+-sensing receptors linked to phospholipase C that mobilize Ca2+ from the ER, exposure of cells to 10 mM Ca2+ did not decrease [Ca2+]Lu but rather raised it. From these findings we conclude that 1) ER Ca2+ release is strictly regulated by feedback inhibition of [Ca2+]c, 2) ER Ca2+ refilling is determined by the rate of Ca2+ influx and occurs mainly in the tiny subplasmalemmal spaces, 3) extracellular Ca2+-induced [Ca2+]c oscillations appear to be triggered not by activation of extracellular Ca2+-sensing receptors but by the ER sensitised by elevated [Ca2+]c and [Ca2+]Lu.
Kang
Yun Kyung
YK
Department of Pathology, Inje University Seoul Paik Hospital, Seoul, Korea
Park
Myoung Kyu
MK
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D020013:Calcium Signaling; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D007424:Intracellular Fluid; D017136:Ion Transport; D008564:Membrane Potentials; D051379:Mice; D046790:Pancreas, Exocrine / Q000166:cytology* / Q000378:metabolism*; D014665:Vasodilator Agents / Q000494:pharmacology
D015220:Calcium Channels; D002614:Chelating Agents; D014665:Vasodilator Agents; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D000109:Acetylcholine; D002118:Calcium