Vijayaraghavan S, Bhattacharyya A, Hoskins D D
Department of Reproductive Biology and Behavior, Oregon Regional Primate Research Center, Beaverton 97006.
Biol Reprod. 1989 Apr;40(4):744-51. doi: 10.1095/biolreprod40.4.744.
Immature caput epididymal sperm accumulate calcium from exogenous sources at a rate 2- to 4-fold greater than mature caudal sperm. Calcium accumulation by these cells, however, is maximal in the presence of lactate as external substrate. This stimulation of calcium uptake by optimum levels of lactate (0.8-1.0 mM) is about 5-fold in caput and 2-fold in caudal sperm compared to values observed with glucose as substrate. Calcium accumulation by intact sperm is almost entirely mitochondrial as evidenced by the inhibition of uptake by rotenone, antimycin, and ruthenium red. The differences in the ability of the various substrates in sustaining calcium uptake appeared to be related to their ability to generate NADH (nicotinamide adenine dinucleotide). Previous reports have documented that mitochondrial calcium accumulation in several somatic cells is regulated by the oxidation state of mitochondrial NADH. A similar situation obtains for bovine epididymal sperm since calcium uptake sustained by site III oxidation of ascorbate in the presence of tetramethyl phenylenediamine and rotenone was also stimulated by NADH-producing substrates, including lactate, and inhibited by substrates generating NAD+ (nicotinamide adenine dinucleotide, oxidized form). Further, calcium uptake by digitonin-permeabilized sperm in the presence of succinate was stimulated when NADH oxidation was inhibited by rotenone. The compounds alpha-keto butyric, valeric, and caproic acids, which generate NAD+, inhibited the maximal calcium uptake observed in the presence of succinate and rotenone, and the hydroxy acids lactate and beta-hydroxybutyrate reversed this inhibition. These results document the regulation of sperm calcium accumulation by the physiological substrate lactate, emphasize the importance of mitochondria in the accumulation of calcium by bovine epididymal sperm, and suggest that the mitochondrial location of the isozyme LDH-X in mammalian sperm may be involved in the regulation of calcium accumulation.
未成熟的附睾头部精子从外源摄取钙的速率比成熟的附睾尾部精子高2至4倍。然而，这些细胞摄取钙的量在以乳酸作为外部底物时达到最大。与以葡萄糖作为底物时相比，最佳水平的乳酸（0.8 - 1.0 mM）对钙摄取的刺激作用在附睾头部精子中约为5倍，在附睾尾部精子中约为2倍。完整精子摄取钙几乎完全是通过线粒体进行的，鱼藤酮、抗霉素和钌红对摄取的抑制作用证明了这一点。各种底物在维持钙摄取能力上的差异似乎与其产生NADH（烟酰胺腺嘌呤二核苷酸）的能力有关。先前的报道表明，几种体细胞中线粒体钙的积累受线粒体NADH氧化状态的调节。牛附睾精子也有类似情况，因为在四甲基对苯二胺和鱼藤酮存在的情况下，抗坏血酸经位点III氧化所维持的钙摄取也受到包括乳酸在内的产生NADH的底物的刺激，并受到产生NAD⁺（烟酰胺腺嘌呤二核苷酸，氧化形式）的底物的抑制。此外，当鱼藤酮抑制NADH氧化时，在琥珀酸存在的情况下，洋地黄皂苷通透的精子摄取钙的量会增加。产生NAD⁺的α - 酮丁酸、戊酸和己酸化合物抑制了在琥珀酸和鱼藤酮存在时观察到的最大钙摄取量，而乳酸和β - 羟基丁酸等羟基酸则逆转了这种抑制作用。这些结果证明了生理底物乳酸对精子钙积累的调节作用，强调了线粒体在牛附睾精子钙积累中的重要性，并表明哺乳动物精子中同工酶LDH - X的线粒体定位可能参与了钙积累的调节。
