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Different expression and activity of the 1 and 4 isoforms of the Na,K-ATPase during rat male germ cell ontogeny

Department of Molecular and Integrative Physiology and ¹ Department of Anatomy and Cell Biology, 3901 Rainbow Boulevard, University of Kansas Medical Center, Kansas City, KS 66160, USA

Correspondence should be addressed to G Blanco; Email: gblanco{at}kumc.edu

Two catalytic isoforms of the Na,K-ATPase, 1 and 4, are present in testis. While 1 is ubiquitously expressed in tissues, 4 predominates in male germ cells. Each isoform has distinct enzymatic properties and appears to play specific roles. To gain insight into the relevance of the Na,K-ATPase isoforms in male germ cell biology, we have studied the expression and activity of 1 and 4 during spermatogenesis and epididymal maturation. This was explored in rat testes at different ages, in isolated spermatogenic cells and in spermatozoa from the caput and caudal regions of the epididymis. Our results show that 1 and 4 undergo differential regulation during development. Whereas 1 exhibits only modest changes, 4 increases with gamete differentiation. The most drastic changes for 4 take place in spermatocytes at the mRNA level, and with the transition of round spermatids into spermatozoa for expression and activity of the protein. No further changes are detected during transit of spermatozoa through the epididymis. In addition, the cellular distribution of 4 is modified with development, being diffusely expressed at the plasma membrane and intracellular compartments of immature cells, finally to localize to the midregion of the spermatozoon flagellum. In contrast, the 1 isoform is evenly present along the plasma membrane of the developing and mature gametes. In conclusion, the Na,K-ATPase 1 and 4 isoforms are functional in diploid, meiotic and haploid male germ cells, 4 being significantly upregulated during spermatogenesis. These results support the importance of 4 in male gamete differentiation and function.