Localization and age-dependent expression of the inward rectifier K+ channel subunit Kir 5.1 in a mammalian reproductive system.

Kir 5.1 is a member of the inward rectifier potassium channel superfamily which does not form functional channels when expressed by itself in Xenopus laevis oocytes. rt-PCR reveals high levels of Kir 5.1 mRNA expression in testis but the function of this channel remains unknown. To determine the cell-specific expression of this channel in the testis we raised a polyclonal antibody against an external epitope of Kir 5.1 and tested its specificity in Xenopus oocytes expressing several cloned Kir subunits. Strong immunoreactivity for Kir 5.1 was found in seminiferous tubules of rat testis and, particularly, in spermatogonia, primary and secondary spermatocytes, spermatids and in the head and body of spermatozoa. The intensity of Kir 5.1 immunofluorescence, quantified using laser scanning microscopy, increased with age at every stage in the development of sperm from spermatogonia and reached a peak in 60-day-old rats. In contrast, the immunofluorescence decreased in 90-day-old animals and was detected mostly in spermatozoa. The results demonstrate that Kir 5.1 expression in the testis is localised to cells involved in spermatogenesis, showing a temporal pattern of expression during sexual maturity.