Mogami H, Tepikin A V, Petersen O H
Medical Research Council Secretory Control Research Group, Physiological Laboratory, University of Liverpool, UK.
EMBO J. 1998 Jan 15;17(2):435-42. doi: 10.1093/emboj/17.2.435.
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.
对激动剂诱发的胞质Ca2+信号终止机制进行了研究。我们测量了胰腺腺泡细胞内质网储存库内的Ca2+浓度，并通过对Ca2+敏感电流进行全细胞膜片钳记录来监测细胞质Ca2+浓度。当通过高浓度的选择性Ca2+缓冲剂将胞质Ca2+浓度钳制在静息水平时，乙酰胆碱会引起细胞内Ca2+储存库的正常排空，但不会增加Ca2+敏感电流。去除乙酰胆碱后，毒胡萝卜素敏感的Ca2+会重新摄取到储存库中，当储存库被加载到刺激前水平时，这个过程就会停止。Ca2+重新摄取的表观速率随着储存库腔内Ca2+浓度的增加而急剧下降，正是这种对Ca2+泵的负反馈控制了Ca2+储存库的含量。在没有细胞质Ca2+钳制的情况下，去除乙酰胆碱会导致升高的细胞质Ca2+浓度迅速恢复到刺激前的静息水平，这早在内质网Ca2+储存库完全重新充满之前就已达到。我们得出结论，通过细胞内储存库内的Ca2+浓度对Ca2+重新摄取的控制允许精确的Ca2+信号终止，而不会干扰储存库的重新填充。
