Changes in distribution of phosphomannosyl receptors during maturation of rat spermatozoa.

The aim of the present work was to study the distribution of the cation-independent (CI) and cation-dependent (CD) mannose-6-phosphate receptors (MPRs) in spermatozoa obtained from either rete testis or three regions of rat epididymis. We observed that both receptors underwent changes in distribution as spermatozoa passed from rete testis to cauda epididymis. CI-MPR was concentrated in the dorsal region of the head in rete testis sperm and that this labeling extended to the equatorial segment of epididymal spermatozoa. CD-MPR, however, changed from a dorsal distribution in rete testis, caput, and corpus to a double labeling on the dorsal and ventral regions in cauda spermatozoa. The percentages of spermatozoa that showed staining for either CI-MPR or CD-MPR increased from rete testis to epididymis. The observed changes were probably the result of a redistribution during transit rather than an unmasking of receptors. The fluorescence corresponding to CD-MPR and CI-MPR on the dorsal region disappeared when caudal spermatozoa underwent the acrosomal reaction. Receptors were localized on the plasmalemma of spermatozoa, as observed by immunoelectron microscopy. Changes in distribution may be related to a maturation process, which suggests new roles for the phosphomannosyl receptors.

Vesicles in rat epididymal fluid. Existence of two populations differing in ultrastructure and enzymatic composition.

Glycosidase activity is very high in rat epididymal fluid as a consequence of the secretory capacity of the epithelium. The mechanism of this secretion is, so far, unknown. Membrane-bound vesicles with activity of beta-galactosidase and N-acetyl-beta-D-glucosaminidase were previously isolated by us from rat epididymal fluid. We report here the existence of two populations of epididymal vesicles separated by centrifugation in a sucrose gradient. They were found to differ in isopicnic equilibrium, size, ultrastructure, and enzymatic activity. Seven days after castration the protein content and specific activities of both enzymes were found decreased in the fractions containing the vesicles. A role in enzyme secretion by the epididymal epithelium is suggested for each vesicle population.