Role of epithelial clear cells of the rat epididymis in the disposal of the contents of cytoplasmic droplets detached from spermatozoa

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Abstract
Upon release from the seminiferous epithelium, spermatoza show a small droplet of cytoplasm attached to the neck region. During transit of spermatozoa in the caput epididymidis, this cytoplasmic droplet migrates along the middle piece of the flagellum. In the corpus epididymidis, the droplet shows a lateral displacement, while in the cauda epididymidis it detaches from the spermatozoon. In the electron microscope, cytoplasmic droplets attached to spermatozoa were seen to contain numerous, short, straight or C-shaped, flattened membranous elements referred to as lamellae, small vesicles, and small particles (35-nm diameter) with a diffuse wall showing no apparent unit membrane. The lamellae were stacked closely on one another or arranged in a loose array. Structurally as well as cytochemically, with different cytochemical markers, the lamellae and vesicular elements failed to show any evidence of being components of the Golgi apparatus or elements of the endoplasmic reticulum. The lamellae, vesicular elements, and 35-nm particles were also seen free in the lumen of the corpus epididymidis but were especially prominent in the cauda epididymidis at a time when droplets were being released from spermatozoa. The lumen of the epididymis, as spermatozoa passed from the caput to the cauda epididymidis, was also noted to acquire progressively a flocculent background material. The epididymal epithelium is composed predominantly of principal and clear cells. The endocytic activity of clear cells was examined in rats at different time intervals after a single injection of cationic ferritin into the lumen of the cauda epididymidis. At 2 min the tracer was bound to the microvilli of these cells and was also observed within large coated and uncoated pits, subsurface coated vesicles, and numerous subsurface small uncoated vesicular membranous elements(150–200-nm diameter). At 5 min, in addition to the above structures, the tracer was present in endosomes, while at 15 and 30 min, pale and dense multivesicular bodies appeared labeled, respectively. At 1 and 2 hr, but more so at 6 hr large dense membrane-bound bodies identified cytochemically as secondary lysosomes became labeled. All of the above endocytic structures were also seen to contain the 35-nm particles, flattened or vesicular membranous profiles, and a fine flocculent background material reminiscent of those seen free in the lumen or found in cytoplasmic droplets attached to spermatozoa. Immunocytochemical results, obtained by using antisera to proteins of outer dense fibers, fibrous sheath, and perforatorium of spermatozoa, revealed a strong reaction in the light microscope over cytoplasmic droplets attached to spermatozoa. Such findings were confirmed to be highly significant compared to controls by using an electron-microscope quantitative approach. A strong immunocytochemical reaction in the light microscope was also noted exclusively over the epithelial clear cells of the epididymis. Such results in conjunction with the morphological findings suggest that in the rat, clear cells have as one of their functions an active role in the uptake and disposal of the contents of cytoplasmic droplets originating from spermatozoa.