Physiology and Pathophysiology of Electrolyte Transport in the Epididymis

Abstract

Although it was eighty years ago that early investigators of the func- tions of the epididymis noted certain differences in the characteristics of the spermatozoa obtained from different regions and proposed that spermatozoa undergo a ‘ripening’ process during their epididymal passage (Tournade 1913), it was not until fifty-five years later that the principle of epididymal maturation of spermatozoa was refined with solid experimental supports (Bedford 1967; Orgebin-Crist 1967, 1969). It is now clear that important maturation changes take place in spermatozoa in the epididymis of most mammals including man and that these changes confer on the sperm the ability to fertilize eggs. Despite this, the mechanisms underlying sperm maturation are still obscure. To date, technological advances have made possible the study of epididymal functions at a cellular and molecular level and have brought light to our understanding of the underlying processes. Significant progress has been made in the area of androgen-regulated genes that control the biosynthesis and secretion of epididymal-specific macromolecules which are integral to the maturation of sperm plasma membrane. Interested readers are referred to the following excellent papers on this topic: Brooks 1987; Ghyselinck et al. 1990; Walker et al. 1990. The present chapter describes some studies made in our own laboratory on epididymal transport of electrolytes and fluid. Undoubtedly, this aspect of epididymal function is equally important for the maintenance of a favourable fluid environment on which sperm maturation and storage depend (Wong et al. 1982; Wong 1986). The introduction of cell culture techniques for the rat (Kierzenbaum et al. 1981, Beyers et al. 1986) and human (Cooper et al. 1990) epididymis facilitated study of the mechanism and regulation of electrolyte transport by the epididymis by the formation of an epithelial sheet on which transepithelial electrical (Cuthbert and Wong 1986; Wong 1988a, 1988b, 1988c), isotope flux (Fu et al. 1990) and microfluorescence (Wong and Huang 1990) measurements can be made on single cells as well as on cell monolayers. Furthermore, epididymal cell culture also permits access of patch-clamp pipettes to the luminal side of the epithelium so that the conductive properties of this membrane and its activation by intracellular messengers can be studied (Cook et a1.1990; Wong 1990c).