Vijayaraghavan S, Trautman K, Mishra S K, Hermsmeyer K
Department of Reproductive Sciences, Oregon Regional Primate Research Center, Beaverton 97006.
Mol Reprod Dev. 1994 Jul;38(3):326-33. doi: 10.1002/mrd.1080380314.
Bovine epididymal sperm resuspended in ionic buffers take up relatively large amounts of calcium. This uptake, which is almost entirely mitochondrial, apparently bypasses the sperm cytosol. The direct mitochondrial loading is an unusual aspect of sperm calcium uptake, which suggests that the plasma membrane region surrounding the mitochondria should be highly permeable to calcium, whereas the membrane domains surrounding the head and tail regions of sperm should be impermeable. This study was undertaken to determine the role of a plasma membrane calcium ATPase in sperm calcium homeostasis. Kinetics of calcium (45Ca2+) uptake into intact and permeabilized caudal epididymal sperm confirmed that mitochondrial calcium uptake occurs with virtually no resistance from the surrounding plasma membrane. Cytoplasmic calcium accumulation by sperm depleted of intracellular ATP, measured in the presence of mitochondrial calcium uptake inhibitors, showed no increase upon energy depletion as would be expected if an ATP-dependent calcium extrusion mechanism were present. Furthermore, lowering the incubation temperature to further reduce the activity of the calcium ATPase in these energy-depleted sperm was also without effect on calcium accumulation. The calcium ATPase inhibitor vanadate, even at high concentrations, failed to increase intracellular 45Ca2+ accumulation. However, vanadate was effective in inhibiting motility showing that the compound was accumulated into sperm to inhibit flagellar dyenin ATPase. Therefore, the lack of effect of vanadate on 45Ca2+ accumulation was not due to its inability to enter sperm. Other calcium ATPase inhibitors such as quercetin, thapsigargin, and cyclopiazonic acid, which readily demonstrate ATP-dependent calcium extrusion in other somatic cells, were also without effect on sperm calcium accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)
悬浮于离子缓冲液中的牛附睾精子会摄取相对大量的钙。这种摄取几乎完全是线粒体的作用，显然绕过了精子胞质溶胶。直接的线粒体钙负载是精子钙摄取的一个不寻常方面，这表明线粒体周围的质膜区域对钙应具有高度通透性，而精子头部和尾部区域周围的膜结构域应是不通透的。本研究旨在确定质膜钙ATP酶在精子钙稳态中的作用。完整和通透的附睾尾精子对钙（45Ca2+）摄取的动力学证实，线粒体钙摄取几乎不受周围质膜的阻力。在存在线粒体钙摄取抑制剂的情况下，测量细胞内ATP耗尽的精子的细胞质钙积累，结果显示能量耗尽时钙积累没有增加，而如果存在ATP依赖的钙外排机制，预计会增加。此外，降低孵育温度以进一步降低这些能量耗尽精子中钙ATP酶的活性，对钙积累也没有影响。钙ATP酶抑制剂钒酸盐即使在高浓度下也未能增加细胞内45Ca2+积累。然而，钒酸盐能有效抑制运动，表明该化合物被积累到精子中以抑制鞭毛动力蛋白ATP酶。因此，钒酸盐对45Ca2+积累缺乏影响并非因其无法进入精子。其他钙ATP酶抑制剂，如槲皮素、毒胡萝卜素和环匹阿尼酸，在其他体细胞中很容易证明其ATP依赖的钙外排作用，但对精子钙积累也没有影响。（摘要截短至250字）
