Surface and surface-to-volume relationships of the Sertoli cell during the cycle of the seminiferous epithelium in the rat.

The surface relationships of the Sertoli cell and the surface relationships of the Sertoli cell in comparison to the changing volumes of developing germ cells were studied using morphometric techniques at periods representing nine groupings of the fourteen defined periods in the cycle of the seminiferous epithelium of the adult rat. No cyclic variation in the total Sertoli plasma membrane surface area was noted. Cyclic variations were noted in the area of the Sertoli cell surface that faces the basal compartment germ cells, but not the basal lamina. No cyclic variations were noted in the amount of contact of the Sertoli cells with each other at the level of the Sertoli cell barrier. However, when areas in the adluminal compartment were studied, significantly less Sertoli-Sertoli contact was seen in stages V through VII than in other stages with the exception of stages II-IV. Surface contact of germ cells with Sertoli cells increased progressively as germ cells entered the intermediate compartment and progressed to late spermatids. However, a calculation of the surface-to-volume ratio showed that surface increases of the Sertoli cell in relation to the volume of germ cells were greatest in elongating spermatids past step 12 of spermiogenesis. The area in which Sertoli ectoplasmic specializations faced germ cells was determined throughout spermatogenesis, and these data demonstrated that the first appearance of ectoplasmic specialization was at the mid-pachytene phase. They also showed that stage VIII was a period when ectoplasmic specialization loss from the cell surface was evident. Less Sertoli ectoplasmic specialization face step 8 and step 19 spermatids than comparable germ cell types at other stages. In addition to Sertoli cell surface area changes during the cycle, volumes of individual germ cell types were determined for the first time. The data presented allow an objective understanding of the complex structure and relationships of the Sertoli cell and provide a basis for understanding functional changes and interpreting biochemical data.