Vijayaraghavan S, Hoskins D D
Department of Reproductive Biology and Behavior, Oregon Regional Primate Research Center, Beaverton 97006.
Gamete Res. 1988 Jul;20(3):343-52. doi: 10.1002/mrd.1120200309.
Secretions from the mammalian epididymis contain proteins that bind to developing sperm and are presumed to play a role in sperm maturation. The biochemical functions in sperm of most of these proteins are not known. In this report we describe the presence of a low molecular weight compound in bovine caudal epididymal luminal fluid (CF) that has a potent stimulatory effect on calcium (45Ca2+) uptake in immature caput epididymal spermatozoa. The studies were initially undertaken to characterize the effect of the protein caltrin, present in bovine seminal plasma (BSP), on calcium uptake into caput spermatozoa. Caltrin is known to block calcium influx into mature bovine sperm. Unexpectedly, the kinetics of calcium uptake into caput sperm showed a biphasic response when treated with BSP, namely, a stimulation of uptake at 1 to 5 min and inhibition of uptake after this time. Since caudal sperm do not show this biphasic response, we reasoned that BSP contained a factor derived from CF that must interact with developing sperm before the binding of caltrin to sperm can prevent further calcium uptake. We first demonstrated that preincubation of caput sperm with CF eliminated the biphasic calcium uptake effect induced in caput sperm by BSP and that caudal fluid alone had a potent stimulatory effect on calcium uptake in caput sperm. Half-maximal stimulation (fivefold over control) occurred at a caudal fluid protein concentration of 0.27 mg/ml. Partial purification of the factor indicates that it is of low molecular weight (MW approximately 1,000), but further chemical characterization has not been carried out and its epididymal site of origin is not known. The results indicate that the regulation of intracellular calcium levels in sperm differs in immature and mature bovine sperm in that an epididymal factor promotes calcium uptake during epididymal maturation, and the seminal fluid protein caltrin prevents it at ejaculation.
哺乳动物附睾的分泌物含有与发育中的精子结合的蛋白质，据推测这些蛋白质在精子成熟过程中发挥作用。其中大多数蛋白质在精子中的生化功能尚不清楚。在本报告中，我们描述了牛尾部附睾管腔液（CF）中存在一种低分子量化合物，该化合物对未成熟的头部附睾精子摄取钙（45Ca2+）具有强烈的刺激作用。这些研究最初旨在表征牛精液血浆（BSP）中存在的钙调蛋白对头部精子摄取钙的影响。已知钙调蛋白可阻止钙流入成熟的牛精子。出乎意料的是，用BSP处理时头部精子摄取钙的动力学呈现双相反应，即在1至5分钟时摄取增加，此后摄取受到抑制。由于尾部精子未表现出这种双相反应，我们推断BSP中含有一种源自CF的因子，该因子必须在钙调蛋白与精子结合之前与发育中的精子相互作用，才能阻止进一步的钙摄取。我们首先证明，用CF预孵育头部精子可消除BSP诱导的头部精子摄取钙的双相效应，并且单独的尾部液体对头部精子摄取钙具有强烈的刺激作用。在尾部液体蛋白质浓度为0.27 mg/ml时出现半数最大刺激（比对照高五倍）。该因子的部分纯化表明其分子量较低（约1,000），但尚未进行进一步的化学表征，其附睾起源部位也未知。结果表明，精子细胞内钙水平的调节在未成熟和成熟的牛精子中有所不同，即附睾因子在附睾成熟过程中促进钙摄取，而精液蛋白质钙调蛋白在射精时阻止钙摄取。
