Increasing information indicates that testosterone actions on cells are mediated not only through the classical intracellular androgen receptor (iAR), but also through membrane androgen receptors (mAR) on cell surfaces. Here, we investigate the expression pattern of mAR and iAR in thymic T cells, which is compared with that of splenic T cells. Thymic T cells are testosterone-sensitive in vivo, i.e. treatment of female C57BL/10 mice with testosterone for 3 weeks decreased the total number of thymic T cells by approximately 90%. The percentage of CD4(-) CD8(-) T cells increased, whereas that of the subsequent CD4(+) CD8(+) T cells was diminished. Flow cytometry and confocal laser scanning microscopy (CLSM) with different anti-iAR antibodies localized iAR predominantly in the cytoplasm, but not on the surface of thymic T cells. The iAR are functionally active since the iAR are induced by testosterone to translocate from cytoplasm to nucleus, and they bind the testosterone analogue 3H-R1881 with high affinity (K(d) approximately 2.2 nM) and saturable capacity (approximately 10,000 binding sites per cell) as determined by Scatchard analysis. By contrast, the impeded ligand testosterone-BSA-FITC (T-BSA-FITC) did not bind to the surface of thymic T cells. In accordance, testosterone was unable to induce any rapid rise in the intracellular free Ca(2+) concentration of Fura-2 loaded thymocytes. This indicates that thymic T cells do not express any significant amounts of mAR. Conversely, splenic T cells express functionally active mAR, whereas their expressed iAR are not functional in the genomic pathway. Our results support the view of a delicately balanced developmental regulation of iAR and mAR in T cells.
Copyright 2002 Elsevier Science Inc.