Evidence against a functional ATP-dependent calcium extrusion mechanism in bovine epididymal sperm.
Evidence against a functional ATP-dependent calcium extrusion mechanism in bovine epididymal sperm.
复制标题
牛附睾精子中功能性 ATP 依赖性钙排出机制的证据。
DOI：
10.1002/mrd.1080380314
复制
发表时间：
1994
影响因子：
2.5
通讯作者：
Hermsmeyer,K
中科院分区：
文献类型：
--
作者：
Vijayaraghavan,S;Trautman,K;Mishra,SK;Hermsmeyer,K
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 to 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 intracellular45Ca2+accumulation. However, vanadate was effective in inhibiting motilty showing that the compound was accumulated into sperm to inhibit flagellar dyenin ATPase. Therefore, the lack of effect of vanadate on45Ca2+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 caclium accumulation. These results with45Ca2+were also confirmed using single‐cell calcium distribution measurements with a fluorescent indicator. Our data strongly suggest that sperm, contrary to previous assumptions, do not possess a functional plasma membrane, ATP‐dependent, calcium extrusion mechanism. © 1994 Wiley‐Liss, Inc.
