APICAL AND NARROW CELLS ARE DISTINCT CELL-TYPES DIFFERING IN THEIR STRUCTURE, DISTRIBUTION, AND FUNCTIONS IN THE ADULT-RAT EPIDIDYMIS

Apical and narrow cells of the initial segment and intermediate zone o f the adult rat epididymis were glutaraldehyde fixed and Epon embedded for routine light (LM) and electron (EM) microscopic analysis and Bou in fixed and paraffin embedded for LM immunocytochemical analysis in o rder to examine their structural features, distribution, and functions . The goblet-shaped apical cells comprised 10.7 = 1.0% of the total ep ithelial population in the proximal initial segment but only 1.3 = 0.5 % in the intermediate zone. In the EM, these cells presented numerous mitochondria; few C-shaped vesicles, and a pale rounder oblong nucleus located in the upper half of their cytoplasm. The slender elongated n arrow cells increased from 2.8 +/- 0.3% in the proximal initial segmen t to 6.3 +/- 0.4% in the intermediate zone. In an EM analysis, these c ells presented numerous C-shaped vesicles and mitochondria and a small flattened nucleus located in the upper half of their cytoplasm. The s tructural features of both these cell types differed not only from eac h other but also from the neighboring principal and basal cells of eac h region. Of the various antibodies examined to lysosomal proteins, na rrow and apical cells expressed high levels of cathepsin D, while beta -hexosaminidase A was expressed at high levels in narrow cells but onl y moderately in apical cells. Apical cells were intensely reactive for the Yf subunit of glutathione-transferase (GST)-P, whereas no reactio n was seen in narrow cells; the Yo subunit of GST was localized within both cell types but only in the proximal initial segment. Narrow cell s exclusively expressed carbonic anhydrase II. Selective differences i n the immunolocalization of these various proteins were also noted bet ween these two cell types and principal and basal cells. The localizat ion of cathepsin D and beta-hexosaminidase A within narrow and apical cells suggests these cells may be involved in the degradation of speci fic proteins within their lysosomes, whereas the presence of GSTs may aid in protecting spermatozoa from a changing environment of harmful e lectrophiles. Localization of carbonic anhydrase II exclusively within narrow cells suggests that these cells may modify the pH of the lumen resulting in the quiescence of sperm motility in the proximal end of the epididymis. Together, the data indicate that apical and narrow cel ls differ not only from each other but also from principal and basal c ells in their structure and relative distribution. They also express d ifferent proteins within the distinct epididymal regions, indicating t hat they perform different functions.