Polarized secretion of androgen-binding protein and transferrin by Sertoli cells grown in a bicameral culture system.

Sertoli cells in vivo are believed to secrete androgen-binding protein (ABP) as well as other proteins in a polarized manner, primarily into the adluminal (apical) compartment of the seminiferous tubules. It is now possible to examine polarized secretion by Sertoli cells in vitro by growing them in dual environment (bicameral) culture chambers such that there is a separation of the apical and basal compartments of the cells. Sertoli cells obtained from 17-day-old rats were grown in these chambers on Millipore filters coated with a reconstituted basement membrane matrix. Within 3 days a confluent epithelial sheet of Sertoli cells (30-40 microns in height) is established, and these cells are joined along their baso-lateral plasma membranes by typical Sertoli-Sertoli tight junctions. We have previously shown that this epithelial sheet of Sertoli cells establishes an electrical resistance, as well as a permeability barrier to small molecules, between the basal and apical compartments of the culture chamber. In the absence of Sertoli cells, proteins equilibrate within 8 h across the matrix-coated filter support. Between 12 and 48 h of culture the Sertoli cell monolayers secrete approximately 4- and 2-fold more ABP and transferrin (Tf), respectively, into the apical compartment than into the basal compartment when grown in serum-free defined medium. ABP secretion is diminished 10-fold by the removal of testosterone from the serum-free defined medium. In addition, the apical/basal ratio of ABP secretion decreases from 4.1 to 1.7 in the absence of testosterone. In contrast, neither the amount nor the direction of Tf secretion is altered by the removal of testosterone. These results demonstrate the bidirectional secretion of ABP and Tf by Sertoli cells grown in bicameral chambers. In addition, the polarity of secretion of these two proteins by Sertoli cells appears to be under differential regulation by testosterone.