Institute of Life Science, Nanchang University, Nanchang, Jiangxi 330031, China.
J Gen Physiol. 2013 Sep;142(3):305-13. doi: 10.1085/jgp.201311011.
During passage through the female reproductive tract, mammalian sperm undergo a maturation process termed capacitation that renders sperm competent to produce fertilization. Capacitation involves a sequence of changes in biochemical and electrical properties, the onset of a hyperactivated swimming behavior, and development of the ability to undergo successful fusion and penetration with an egg. In mouse sperm, the development of hyperactivated motility is dependent on cytosolic alkalization that then results in an increase in cytosolic Ca(2+). The elevation of Ca(2+) is thought to be primarily driven by the concerted interplay of two alkalization-activated currents, a K(+) current (KSPER) composed of pore-forming subunits encoded by the Kcnu1 gene (also termed Slo3) and a Ca(2+) current arising from a family of CATSPER subunits. After deletion of any of four CATSPER subunit genes (CATSPER1-4), the major remaining current in mouse sperm is alkalization-activated KSPER current. After genetic deletion of the Slo3 gene, KSPER current is abolished, but there remains a small voltage-activated K(+) current hypothesized to reflect monovalent flux through CATSPER. Here, we address two questions. First, does the residual outward K(+) current present in the Slo3 (-/-) sperm arise from CATSPER? Second, can any additional membrane K(+) currents be detected in mouse sperm by patch-clamp methods other than CATSPER and KSPER? Here, using mice bred to lack both SLO3 and CATSPER1 subunits, we show conclusively that the voltage-activated outward current present in Slo3 (-/-) sperm is abolished when CATSPER is also deleted. Any leak currents that may play a role in setting the resting membrane potential in noncapacitated sperm are likely smaller than the pipette leak current and thus cannot be resolved within the limitation of the patch-clamp technique. Together, KSPER and CATSPER appear to be the sole ion channels present in mouse sperm that regulate membrane potential and Ca(2+) influx in response to alkalization.
在通过女性生殖道的过程中，哺乳动物精子经历了一个成熟过程，称为获能，使精子有能力产生受精。获能涉及一系列生化和电性质的变化、开始超激活游动行为以及发展与卵子成功融合和穿透的能力。在小鼠精子中，超激活运动的发展依赖于细胞质的碱化，随后导致细胞质 Ca(2+)的增加。Ca(2+)的升高被认为主要是由两种碱化激活电流的协同相互作用驱动的，一种是由 Kcnu1 基因（也称为 Slo3）编码的孔形成亚基组成的 K(+)电流 (KSPER)，另一种是来自 CATSPER 亚基家族的 Ca(2+)电流。在删除任何四个 CATSPER 亚基基因（CATSPER1-4）之一后，小鼠精子中的主要剩余电流是碱化激活的 KSPER 电流。在 Slo3 基因被遗传删除后，KSPER 电流被废除，但仍然存在一种小的电压激活的 K(+)电流，据推测反映了 CATSPER 中的单电荷通量。在这里，我们解决两个问题。首先，Slo3(-/-)精子中存在的残留外向 K(+)电流是否来自 CATSPER？其次，除了 CATSPER 和 KSPER 之外，通过膜片钳方法是否可以在小鼠精子中检测到任何其他膜 K(+)电流？在这里，我们使用繁殖缺乏 SLO3 和 CATSPER1 亚基的小鼠表明，当 CATSPER 也被删除时，Slo3(-/-)精子中存在的电压激活外向电流被废除。在非获能精子中可能对静息膜电位起作用的任何漏电流可能比管腔漏电流小，因此在膜片钳技术的限制内无法解决。总之，KSPER 和 CATSPER 似乎是存在于小鼠精子中的唯一离子通道，它们调节膜电位和 Ca(2+)流入以响应碱化。
