Increased luminal pH in the epididymis of infertile c‐ros knockout mice and the expression of sodium–hydrogen exchangers and vacuolar proton pump H+‐ATPase

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Abstract
Transgenic mice targeted for the c‐ros gene, which are fertile when heterozygous (HET), but infertile when homozygous (knockout, KO) and associated with failure in pubertal differentiation of the epididymal initial segment, provide a model for studying the role of the epididymal luminal environment in sperm development. Luminal fluid from the cauda epididymidis was measured by both ion‐selective microelectrodes and pH strips to be 0.3 pH units higher in the KO than HET. Of the genes responsible for luminal acidification, expression of mRNA of vacuolar H+‐ATPase was found in all epididymal regions, but with no difference between KO and HET. Immunohistochemistry showed its presence in epithelial apical cells and clear cells. The Na+–hydrogen exchanger NHE2 was expressed at mRNA and protein levels in the caput but only marginally detectable if at all in the distal epididymis. This was compensated for by NHE3 which was expressed strongest in the cauda region, in agreement with immunohistochemical staining. Quantification of Western blot data revealed slight, but significant, decreases of NHE2 in the caput and of NHE3 in the cauda in the KO mice. The increase in luminal fluid pH in the KO mice could also be contributed to by other epithelial regulating factors including the Na+‐dependent glutamate transporter EAAC1 formerly reported to be down regulated in the KO. Mol. Reprod. Dev. 68: 159–168, 2004.