Korc M, Schöni M H
Proc Natl Acad Sci U S A. 1987 Mar;84(5):1282-5. doi: 10.1073/pnas.84.5.1282.
The effects of extracellular phosphate and lanthanum on cytosolic free Ca2+ [( Ca2+]i) levels were studied in isolated rat pancreatic acini. In the presence of 1.28 mM Ca2+ and 1.0 mM phosphate, the mean resting [Ca2+]i level was 120 nM. Omission of phosphate from incubation medium significantly lowered this value to 94 nM. The gastrointestinal hormone cholecystokinin octapeptide (CCK-8) rapidly enhanced both [Ca2+]i levels and 45Ca2+ efflux, irrespective of the presence or absence of phosphate. Lanthanum (0.1 mM), a compound known to block transmembrane Ca2+ fluxes, attenuated both actions of CCK-8, but only in the absence of extracellular phosphate. There was a concomitant decrease in amylase secretion induced by 0.1 nM CCK-8 but not by 10 nM CCK-8, without a significant change in cellular ATP levels. The inhibitory actions of lanthanum on CCK-8-stimulated [Ca2+]i levels were very rapid and were mimicked only by prolonged incubation of acini in Ca2+-free medium supplemented with EGTA. Omission of phosphate from incubation medium also lowered basal [Ca2+]i levels in IM-9 lymphocytes. These findings suggest that extracellular phosphate may modulate resting [Ca2+]i levels in pancreatic acini and other cell types and that mobilization of intracellular Ca2+ may partly depend on the availability of a lanthanum-sensitive pool of cell-surface Ca2+ that is not readily removed by EGTA.
在分离的大鼠胰腺腺泡中研究了细胞外磷酸盐和镧对胞质游离钙离子[Ca2+]i水平的影响。在存在1.28 mM钙离子和1.0 mM磷酸盐的情况下，平均静息[Ca2+]i水平为120 nM。从孵育培养基中去除磷酸盐可使该值显著降低至94 nM。胃肠激素八肽胆囊收缩素（CCK-8）可迅速提高[Ca2+]i水平和45Ca2+外流，无论是否存在磷酸盐。镧（0.1 mM）是一种已知可阻断跨膜钙离子通量的化合物，可减弱CCK-8的两种作用，但仅在细胞外无磷酸盐时有效。由0.1 nM CCK-8诱导的淀粉酶分泌随之减少，但10 nM CCK-8诱导的淀粉酶分泌则未减少，细胞ATP水平无显著变化。镧对CCK-8刺激的[Ca2+]i水平的抑制作用非常迅速，只有在补充EGTA的无钙培养基中长时间孵育腺泡才能模拟这种作用。从孵育培养基中去除磷酸盐也会降低IM-9淋巴细胞的基础[Ca2+]i水平。这些发现表明，细胞外磷酸盐可能调节胰腺腺泡和其他细胞类型的静息[Ca2+]i水平，并且细胞内钙离子的动员可能部分取决于一种对镧敏感的细胞表面钙离子池的可用性，该钙离子池不易被EGTA去除。
