Thundathil Jacob C, Anzar Muhammad, Buhr Mary M
Department of Animal and Poultry Science, University of Guelph, Ontario, Canada N1G 2W1.
Biol Reprod. 2006 Sep;75(3):308-17. doi: 10.1095/biolreprod.105.047852. Epub 2006 May 10.
A heteromeric integral membrane protein, Na+/K+ATPase is composed of two polypeptides, alpha and beta, and is active in many cell types, including testis and spermatozoa. It is a well-known ion transporter, but binding of ouabain, a specific inhibitor of Na+/K+ATPase, to Na+/K+ATPase in somatic cells initiates responses that are similar to signaling events associated with bovine sperm capacitation. The objectives of the present study were to demonstrate the presence of Na+/K+ATPase in bovine sperm and to investigate its role in the regulation of bovine sperm capacitation. The presence of Na+/K+ATPase in sperm from mature Holstein bulls was demonstrated by immunoblotting and immunocytochemistry using a monoclonal antibody developed in mouse against the beta 1 polypeptide of Na+/K+ATPase. Binding of ouabain to Na+/K+ATPase inhibited motility (decreased progressive motility, average path velocity, and curvilinear velocity) and induced tyrosine phosphorylation and capacitation but did not increase intracellular calcium levels in spermatozoa. Furthermore, binding of ouabain to Na+/K+ATPase induced depolarization of sperm plasma membrane. Therefore, binding of ouabain to Na+/K+ATPase induced sperm capacitation through depolarization of sperm plasma membrane and signaling via the tyrosine phosphorylation pathway without an appreciable increase in intracellular calcium. To our knowledge, this is the first report concerning the signaling role of Na+/K+ATPase in mammalian sperm capacitation.
钠钾ATP酶是一种异源整合膜蛋白，由α和β两条多肽组成，在包括睾丸和精子在内的多种细胞类型中具有活性。它是一种著名的离子转运体，但哇巴因（钠钾ATP酶的一种特异性抑制剂）与体细胞中的钠钾ATP酶结合会引发一些反应，这些反应类似于与牛精子获能相关的信号事件。本研究的目的是证明牛精子中存在钠钾ATP酶，并研究其在调节牛精子获能中的作用。使用在小鼠中制备的针对钠钾ATP酶β1多肽的单克隆抗体，通过免疫印迹和免疫细胞化学方法证明了来自成熟荷斯坦公牛精子中存在钠钾ATP酶。哇巴因与钠钾ATP酶的结合抑制了精子活力（降低了前向运动能力、平均路径速度和曲线速度），并诱导了酪氨酸磷酸化和获能，但并未增加精子细胞内的钙水平。此外，哇巴因与钠钾ATP酶的结合诱导了精子质膜的去极化。因此，哇巴因与钠钾ATP酶的结合通过精子质膜的去极化和酪氨酸磷酸化途径的信号传导诱导了精子获能，而细胞内钙没有明显增加。据我们所知，这是关于钠钾ATP酶在哺乳动物精子获能中的信号作用的首次报道。
