Maruyama Y, Inooka G, Li Y X, Miyashita Y, Kasai H
Department of Physiology, Jichi Medical School, Tochigi, Japan.
EMBO J. 1993 Aug;12(8):3017-22. doi: 10.1002/j.1460-2075.1993.tb05970.x.
We investigated how agonist-induced patterned rises in cytosolic Ca2+ concentration ([Ca2+]i) regulate exocytotic secretion in the rat pancreatic acinar cell. The distribution of [Ca2+]i was visualized with a confocal microscope, which revealed that a Ca2+ ionophore, A23187, induced slow and homogeneous [Ca2+]i rises, while acetylcholine (ACh) always triggered primary Ca2+ spikes at the granular area which bears secretory granules. Secretion was monitored by measuring capacitance with the patch clamp method. Errors in the estimates of membrane capacitance (C) due to changes in conductance (G) were experimentally as well as theoretically evaluated to be one-tenth of the actual signals. We found that A23187 raised G without changing C at a low concentration, while it triggered asynchronous rises in G and C with lags in C, at a high concentration. By contrast, ACh triggered simultaneous rapid rises in G and C. Our results support the hypothesis that exocytotic secretion is less sensitive to Ca2+ than to ion channels and is directly caused by agonist-induced primary Ca2+ spikes at the granular area. It is therefore suggested that spatio-temporal patterns of Ca2+ oscillations could play a key role in exocytotic secretion from the exocrine acinar cell.
我们研究了激动剂诱导的胞质Ca2+浓度（[Ca2+]i）的模式性升高如何调节大鼠胰腺腺泡细胞的胞吐分泌。用共聚焦显微镜观察[Ca2+]i的分布，结果显示Ca2+离子载体A23187诱导[Ca2+]i缓慢且均匀地升高，而乙酰胆碱（ACh）总是在含有分泌颗粒的颗粒区域引发初级Ca2+尖峰。通过膜片钳法测量电容来监测分泌。通过实验和理论评估发现，由于电导（G）变化导致的膜电容（C）估计误差为实际信号的十分之一。我们发现，低浓度时A23187升高G但不改变C，而高浓度时它会引发G和C的异步升高，且C有滞后。相比之下，ACh引发G和C同时快速升高。我们的结果支持这样的假设，即胞吐分泌对Ca2+的敏感性低于对离子通道的敏感性，并且直接由激动剂在颗粒区域诱导的初级Ca2+尖峰引起。因此，提示Ca2+振荡的时空模式可能在外分泌腺泡细胞的胞吐分泌中起关键作用。
