Termination of cytosolic Ca2+ signals: Ca2+ reuptake into intracellular stores is regulated by the free Ca2+ concentration in the store lumen.
The mechanism by which agonist-evoked cytosolic Ca2+ signals are terminated has been investigated. We measured the Ca2+ concentration inside the endoplasmic reticulum store of pancreatic acinar cells and monitored the cytoplasmic Ca2+ concentration by whole-cell patch-clamp recording of the Ca2+-sensitive currents. When the cytosolic Ca2+ concentration was clamped at the resting level by a high concentration of a selective Ca2+ buffer, acetylcholine evoked the usual depletion of intracellular Ca2+ stores, but without increasing the Ca2+-sensitive currents. Removal of acetylcholine allowed thapsigargin-sensitive Ca2+ reuptake into the stores, and this process stopped when the stores had been loaded to the pre-stimulation level. The apparent rate of Ca2+ reuptake decreased steeply with an increase in the Ca2+ concentration in the store lumen and it is this negative feedback on the Ca2+ pump that controls the Ca2+ store content. In the absence of a cytoplasmic Ca2+ clamp, acetylcholine removal resulted in a rapid return of the elevated cytoplasmic Ca2+ concentration to the pre-stimulation resting level, which was attained long before the endoplasmic reticulum Ca2+ store had been completely refilled. We conclude that control of Ca2+ reuptake by the Ca2+ concentration inside the intracellular store allows precise Ca2+ signal termination without interfering with store refilling.
Mogami
H
H
Medical Research Council Secretory Control Research Group, Physiological Laboratory, University of Liverpool, UK.
Tepikin
A V
AV
Petersen
O H
OH
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000378:metabolism; D002469:Cell Separation; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D007424:Intracellular Fluid / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D051379:Mice; D010179:Pancreas / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015398:Signal Transduction / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology
D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D000109:Acetylcholine; D002118:Calcium