Streb H, Schulz I
Am J Physiol. 1983 Sep;245(3):G347-57. doi: 10.1152/ajpgi.1983.245.3.G347.
Ca2+ uptake into isolated exocrine pancreatic cells with highly permeable plasma membrane was determined by measuring the decrease in free Ca2+ concentration of the surrounding incubation medium with a Ca2+-specific electrode. In the presence of Mg-ATP and respiratory substrates the free Ca2+ concentration of the incubation medium decreased rapidly after addition of leaky cells until a stable medium free Ca2+ concentration of 4.2 +/- 0.1 X 10(-7) mol/l was obtained. Changes in the medium free Ca2+ concentration at steady state by addition of Ca2+ or EGTA were buffered by cellular uptake or release, respectively, until the steady-state free Ca2+ concentration was reestablished. When nonmitochondrial Ca2+ uptake was determined in the presence of a combination of mitochondrial inhibitors (10(-5) mol/l antimycin, 5 X 10(-6) mol/l oligomycin, and 10(-2) mol/l azide), the rate of uptake was considerably reduced, while the steady-state concentration was unaltered. In contrast, mitochondrial uptake that could be observed in the presence of the ATPase inhibitor vanadate (2 X 10(-3) mol/l) proceeded at the same rate as the control, but the minimal medium free Ca2+ concentration reached was 2.4 +/- 0.1 X 10(-7) mol/l higher than the control. Addition of secretagogues at steady-state free Ca2+ concentration resulted in a Ca2+ release of 0.73 +/- 0.08 nmol/mg protein. The increase in medium free Ca2+ concentration was entirely transient and followed by reuptake to the prestimulation level. The data indicate that a cytosolic free Ca2+ concentration of 4 X 10(-7) mol/l can be regulated in pancreatic acinar cells by a nonmitochondrial Mg2+-dependent Ca2+ pool.
通过使用钙离子特异性电极测量周围孵育介质中游离钙离子浓度的降低，来测定具有高渗透性质膜的离体胰腺外分泌细胞对钙离子的摄取。在存在镁 - 三磷酸腺苷（Mg - ATP）和呼吸底物的情况下，加入有渗漏的细胞后，孵育介质中的游离钙离子浓度迅速下降，直至获得稳定的介质游离钙离子浓度为4.2±0.1×10⁻⁷mol/L。在稳态下，通过加入钙离子或乙二醇双四乙酸（EGTA）引起的介质游离钙离子浓度变化，分别通过细胞摄取或释放来缓冲，直到重新建立稳态游离钙离子浓度。当在存在线粒体抑制剂组合（10⁻⁵mol/L抗霉素、5×10⁻⁶mol/L寡霉素和10⁻²mol/L叠氮化物）的情况下测定非线粒体钙离子摄取时，摄取速率显著降低，而稳态浓度未改变。相反，在存在三磷酸腺苷酶（ATPase）抑制剂钒酸盐（2×10⁻³mol/L）的情况下可观察到的线粒体摄取，其进行速率与对照相同，但达到的最低介质游离钙离子浓度比对照高2.4±0.1×10⁻⁷mol/L。在稳态游离钙离子浓度下加入促分泌剂导致钙离子释放量为0.73±0.08nmol/mg蛋白质。介质游离钙离子浓度的增加完全是短暂的，随后再摄取至刺激前水平。数据表明，胰腺腺泡细胞中4×10⁻⁷mol/L的胞质游离钙离子浓度可由非线粒体镁离子依赖性钙离子池调节。
