The role of Na,K‐ATPase in human sperm motility

A fourth Na,K‐ATPase α isoform, which was found to be abundant in testes, was proved to be a catalytical subunit of the enzyme. Recently, it has been shown that the α 4 isoform along with α 1 is expressed in the midpiece of the flagellum of mature rat sperm and the inhibition of α 4 with ouabain led to sperm immotility. In this study, sperm from 135 males with normal semen profile and 50 males with oligoasthenospermia were treated with 10–5 and 10–2 M ouabain solutions to inhibit α 4, and α 4 plus α 1 isoforms, respectively. In males with normal semen profile, sperm motility has been demonstrated to decrease with time to almost the same level with both ouabain solutions. In oligoasthenospermic males motility was also found almost completely lost. These observations showed us that the α 4 isoform may be held responsible for human sperm motility.When sperm plasma membrane Na,K‐ATPase activity was assayed for both normal and oligoasthenospermic males, a significant decrease in enzyme activity of males with oligoasthenospermia was observed (p < 0.05). In our recent study, sperm motility was found decreased by treatment with peroxynitrite (ONOO–). To investigate the effect of ONOO– on sperm Na,K‐ATPase activity, sperm plasma membranes were treated with 100 μM ONOO– and plasma membrane Na,K‐ATPase activity was observed to be significantly decreased (p < 0.05). Although total sulfhydryl (SH) content of sperm plasma membrane was also found significantly lower, no correlation was found between Na,K‐ATPase activity and SH content.