Expression and localization of PMCA4 in rat testis and epididymis

It has recently been shown in mice that the plasma membrane Ca(2+)-ATPase isoform 4 (PMCA4) is essential for sperm fertilization capacity. We analyzed whether sperm PMCA4 is formed in the rat during spermatogenesis or is synthesized in the epididymis and transferred onto sperm during sperm maturation. We could show that PMCA4 is conserved in sperm from testis to epididymis. In testis, PMCA4 mRNA was restricted to spermatogonia and early spermatocytes, while the PMCA4 protein was detected in spermatogonia, late spermatocytes, spermatids and in epididymal sperm. In epididymis PMCA4 mRNA was localized in basolateral plasma membranes of epithelial cells of the caput, corpus and cauda epididymidis. In contrast, the protein was only detectable in the epithelial cells of the caput, indicating that PMCA4 mRNA is only translated into protein in caput epithelium. In the epididymal corpus and cauda, PMCA4 mRNA and protein, respectively, was localized and in peritubular cells. Furthermore, we detected an identical distribution of PMCA4a and b splice variants in rat testis, epididymal corpus and cauda. In the caput epididymidis, where PMCA4 is located in the epithelium splice variant 4b was more prominent. Further experiments have to clarify the functional importance of the differences in the PMCA4 distribution.