Light cells within the limiting membrane of rat seminiferous tubules

Light-staining cells, distinct from myoid cells, were identified in electron micrographs of the limiting membrane of rat seminiferous tubules. While these cells were also found free in the interstitial space, they were observed mostly in the myoid cell layer of the limiting membrane but were never seen within the seminiferous epithelium itself. The light cells were characterized by a pale-stained cytoplasm containing a spheroidal Golgi apparatus next to a polymorphous often kidney-shaped nucleus, a few cisternae of rough endoplasmic reticulum and some granules of various types including multivesicular bodies. In hematoxylin-stained whole mounts of dissected tubules, these light cells were readily identified under the light microscope by nuclear morphology and light-staining juxtanuclear Golgi apparatus. The incidence of these cells, per unit surface area of tubular wall, was calculated, taking into consideration the stages of the cycle of the seminiferous epithelium with which they were associated. Distributed along the entire length of seminiferous tubules, their number varied significantly during the cycle. Low numbers were found in stages II–IV and XIII of the cycle, while high numbers were found in stages IX to XII and XIV–I of the cycle. These observations indicate that the seminiferous epithelium may exert an influence on the population of light cells present in the tubular limiting membrane.