Department of Regulatory Physiology, Dokkyo Medical University 880 Kitakobayashi, Mibu-Machi, Shimotsuga-gun, Tochigi, 321-0293Japan.
Laboratory Animal Research Center, Dokkyo Medical University 880 Kitakobayashi, Mibu-Machi, Shimotsuga-gun, Tochigi, 321-0293Japan.
Zygote. 2021 Feb;29(1):66-74. doi: 10.1017/S0967199420000532. Epub 2020 Oct 5.
Mammalian sperm have to undergo capacitation to be fertilization competent. Capacitated sperm in vitro show hyperpolarization of the membrane potential. It has been reported that in mouse membrane hyperpolarization is necessary for the acrosome reaction. We recently found that the fluid of the hamster oviduct, where fertilization occurs, contained a high potassium (K+) concentration (~20 mEq/l). This high K+ concentration could depolarize the membrane potential and prevent the acrosome reaction/fertilization. Conversely, some beneficial effects on capacitation of high K+ concentration or a high K/Na ratio were also reported. In the present study, we investigated the effects of oviduct high K+ concentration on hamster sperm capacitation-associated events and fertilization. The present study confirmed that, in hamster sperm, membrane potential was hyperpolarized upon in vitro capacitation, indicating that capacitation-associated hyperpolarization is a universal phenomenon among mammalian species. An increase in KCl concentration in the medium to 20 mM significantly depolarized the membrane potential and suppressed hyperpolarization when in the presence of >101 mM NaCl. However, an increase in the KCl concentration to 20 mM did not significantly affect the percentage of motile sperm, hyperactivation or the acrosome reaction. No effect of 20 mM KCl on in vitro fertilization was observed. In addition, no correlative changes in hyperactivation and the acrosome reaction with K/Na ratio were observed. These results suggested that in hamsters the oviduct K+ concentration suppressed hyperpolarization but had no effect on capacitation and in vitro fertilization. Our results raised a question over the physiological significance of capacitation-associated hyperpolarization.
哺乳动物精子必须经历获能才能具有受精能力。体外获能的精子表现出膜电位的超极化。据报道，在小鼠中，膜超极化是顶体反应所必需的。我们最近发现，受精发生的仓鼠输卵管中的液体含有高钾（K+）浓度（~20 mEq/l）。这种高 K+浓度可以使膜电位去极化，并阻止顶体反应/受精。相反，也有报道称高 K+浓度或高 K/Na 比具有一些有益于获能的作用。在本研究中，我们研究了输卵管高 K+浓度对仓鼠精子获能相关事件和受精的影响。本研究证实，在仓鼠精子中，体外获能会导致膜电位超极化，表明获能相关的超极化是哺乳动物物种中的普遍现象。将培养基中的 KCl 浓度增加到 20 mM 会显著去极化膜电位，并在存在 >101 mM NaCl 时抑制超极化。然而，将 KCl 浓度增加到 20 mM 不会显著影响运动精子的百分比、超激活或顶体反应。在体外受精中未观察到 20 mM KCl 的作用。此外，K/Na 比值的变化与超激活和顶体反应之间没有相关性。这些结果表明，在仓鼠中，输卵管中的 K+浓度抑制了超极化，但对获能和体外受精没有影响。我们的结果提出了一个问题，即获能相关的超极化的生理意义是什么。
