Parotid microsomal Ca2+ transport. Subcellular localization and characterization.
Parotid microsomal Ca2+ transport. Subcellular localization and characterization.
复制标题
腮腺微粒体 Ca2 运输。
作者：
P. Kanagasuntheram;T. Teo
通过差速离心将大鼠腮腺匀浆分级为线粒体、重微粒体和轻微粒体级分。亚细胞部分对 ATP 依赖性 45Ca2+ 的吸收与 NADPH-细胞色素 c 还原酶（一种与内质网相关的酶）的分布平行。 Ca2+ 吸收率最高的是重微粒体部分。该部分的 Ca2+ 吸收取决于 ATP 的存在，并通过 5 mM 草酸盐以线性速率维持。线粒体 Ca2+ 转运抑制剂对 Ca2+ 吸收率没有影响。 Na+ 和 K+ 刺激 Ca2+ 的吸收。在最佳浓度下。 Na+ 刺激 Ca2+ 吸收 120%，K+ 刺激 Ca2+ 吸收 260%。将 pH 从 7.4 降低至 6.8 对 Ca2+ 吸收几乎没有影响。 Ca2+ 吸收的 Km 为 3.7 µM 游离 Ca2+ 和 0.19 mM-ATP。钒酸盐抑制Ca2+的吸收； 60μM钒酸盐抑制Ca2+积累率50%。结论是ATP依赖性Ca2+转运系统位于内质网，可能在维持细胞内游离Ca2+水平在较窄的浓度范围内发挥作用。
Rat parotid gland homogenates were fractionated into mitochondrial, heavy microsomal and light microsomal fractions by differential centrifugation. ATP-dependent 45Ca2+ uptake by the subcellular fractions paralleled the distribution of NADPH-cytochrome c reductase, an enzyme associated with the endoplasmic reticulum. The highest rate of Ca2+ uptake was found in the heavy microsomal fraction. Ca2+ uptake by this fraction was dependent on the presence of ATP and was sustained at a linear rate by 5 mM-oxalate. Inhibitors of mitochondrial Ca2+ transport had no effect on the rate of Ca2+ uptake. Na+ and K+ stimulated Ca2+ uptake. At optimal concentrations. Na+ stimulated Ca2+ uptake by 120% and K+ stimulated Ca2+ uptake by 260%. Decreasing the pH from 7.4 to 6.8 had little effect on Ca2+ uptake. The Km for Ca2+ uptake was 3.7 microM free Ca2+ and 0.19 mM-ATP. Vanadate inhibited Ca2+ uptake; 60 microM-vanadate inhibited the rate of Ca2+ accumulation by 50%. It is concluded that the ATP-dependent Ca2+ transport system is located on the endoplasmic reticulum and may play a role in maintaining intracellular levels of free Ca2+ within a narrow range of concentration.