Hughes Elizabeth, Lee Andy K, Tse Amy
Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Endocrinology. 2006 Mar;147(3):1396-407. doi: 10.1210/en.2005-1023. Epub 2005 Dec 8.
The exocytosis of insulin-containing granules from pancreatic beta-cells is tightly regulated by changes in cytosolic Ca2+ concentration ([Ca2+]i). We investigated the role of the sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) pump, Na+/Ca2+ exchanger, and plasma membrane Ca2+-ATPase pump in the Ca2+ dynamics of single rat pancreatic beta-cells. When the membrane potential was voltage clamped at -70 mV (in 3 mm glucose at approximately 22 or 35 C), SERCA pump inhibition dramatically slowed (approximately 4-fold) cytosolic Ca2+ clearance and caused a sustained rise in basal [Ca2+]i via the activation of capacitative Ca2+ entry. SERCA pump inhibition increased ( approximately 1.8-fold) the amplitude of the depolarization-triggered Ca2+ transient at approximately 22 C. Inhibition of the Na+/Ca2+ exchanger or plasma membrane Ca2+-ATPase pump had only minor effects on Ca2+ dynamics. Simultaneous measurement of [Ca2+]i and exocytosis (with capacitance measurement) revealed that SERCA pump inhibition increased the magnitude of depolarization-triggered exocytosis. This enhancement in exocytosis was not due to the slowing of the cytosolic Ca2+ clearance but was closely correlated to the increase in the peak of the depolarization-triggered Ca2+ transient. When compared at similar [Ca2+]i with controls, the rise in basal [Ca2+]i during SERCA pump inhibition did not cause any enhancement in the magnitude of the ensuing depolarization-triggered exocytosis. Therefore, we conclude that in rat pancreatic beta-cells, the rapid uptake of Ca2+ by SERCA pump limits the peak amplitude of depolarization-triggered [Ca2+]i rise and thus controls the amount of insulin secretion.
胰腺β细胞中含胰岛素颗粒的胞吐作用受到胞质Ca2+浓度（[Ca2+]i）变化的严格调控。我们研究了肌浆网Ca2+-ATP酶（SERCA）泵、Na+/Ca2+交换体和质膜Ca2+-ATP酶泵在单个大鼠胰腺β细胞Ca2+动力学中的作用。当膜电位钳制在-70 mV（在约22或35℃的3 mM葡萄糖中）时，SERCA泵抑制显著减慢（约4倍）胞质Ca2+清除，并通过激活容量性Ca2+内流导致基础[Ca2+]i持续升高。在约22℃时，SERCA泵抑制使去极化触发的Ca2+瞬变幅度增加（约1.8倍）。抑制Na+/Ca2+交换体或质膜Ca2+-ATP酶泵对Ca2+动力学仅有轻微影响。同时测量[Ca2+]i和胞吐作用（通过电容测量）表明，SERCA泵抑制增加了去极化触发的胞吐作用的幅度。胞吐作用的这种增强并非由于胞质Ca2+清除减慢，而是与去极化触发的Ca2+瞬变峰值的增加密切相关。当在相似的[Ca2+]i下与对照相比时，SERCA泵抑制期间基础[Ca2+]i的升高并未导致随后去极化触发的胞吐作用幅度的任何增强。因此，我们得出结论，在大鼠胰腺β细胞中，SERCA泵对Ca2+的快速摄取限制了去极化触发的[Ca2+]i升高的峰值幅度，从而控制胰岛素分泌量。
