Sperm Na⁺, K⁺-ATPase α4 and plasma membrane Ca²⁺-ATPase (PMCA) 4 regulation in asthenozoospermia

Asthenozoospermia, which is characterized by reduced motility, is one of the etiologies of male infertility. Its biochemical and functional consequences include altered ATPase activity. This study investigated the activities of Na⁺, K⁺-ATPase and Ca²⁺-ATPase and the expression of Na⁺, K⁺-ATPase α4 and PMCA4 isoforms in human sperm of asthenozoospermic infertile men. Nineteen samples from asthenozoospermic infertile couples were examined in this study. Computerized-assisted semen analysis (CASA) was performed, and the enzyme activity was measured based on the ability of ATPase to release organic phosphate from ATP as a substrate. The Na⁺, K⁺-ATPase α4 and PMCA4 isoform expression levels were measured by western immunoblotting, whereas the protein distribution was examined by immunocytochemistry. This showed that the Na⁺, K⁺-ATPase activity and the Na⁺, K⁺-ATPase α4 isoform expression were lower in the asthenozoospermia group than in the normozoospermia group (8.688±1.161 versus 13.851±1.884 µmol Pi/mg protein/h, respectively; p>0.05). In contrast, the Ca²⁺-ATPase activity was significantly higher in the asthenozoospermia group than in the normozoospermia group (11.154±1.186 versus 2.725±0.545 µmol Pi/mg protein/h, respectively; p<0.05). In comparison, PMCA4 expression in the asthenozoospermia group was lower than in the normozoospermia group (p>0.05). The altered ATPase activity and isoform expression in asthenozoospermia may impair sperm structure and function.