L-type voltage-operated Ca+2 channels modulate transient Ca +2 influx triggered by activation of sertoli cell surface L-selectin

Near the base of mammalian seminiferous epithelium, Sertoli cells are joined by tight junctions, which constitute the blood-testis barrier. Differentiating germ cells are completely enveloped by Sertoli cells and must traverse the tight junctions during spermatogenic cycle. Fol lowing the specific ligand activation of L-selectin, the up-regulated Rho family small G-proteins have been implicated as important modulators of tight junctional dynamics. Although the activation of L-selectin transmits subsequent intracellular signals in a Ca⁺²-dependent fashion in various cell types, little is understood regarding the signaling pathways utilized by L-selectin in Sertoli cells. Therefore, we have examined the possible resultant calcium influx triggered by specific ligand-activation of cell surface L-selectin receptors or by cross-linking of L-selectin with anti-L-selectin. Spectrofluorimetric studies demonstrate increase of intracellular Ca⁺² levels immediately after the treatment of the L-selectin ligands, fucoidan and sialyl Lewis-a, or after treatment with anti-L-selectin antibody. We then determined the mechanism of Ca⁺² influx by investigating L- and T-type voltage-operated Ca ⁺² channels, which have been suggested to present in the membranes of Sertoli cells. Data demonstrate that Sertoli cells treated with L-type voltage-operated Ca⁺² channel antagonists, nifedipine, diltiazem, or verapamil, lead to dose-dependent blockage of L-selectin-induced Ca⁺² influx. Cells treated with mibedradil, a T-type voltage-operated Ca ⁺² channel antagonist, results in little or no blocking effect. Therefore, we conclude that activation of Sertoli cell L-selectin induces Ca⁺² influx, which is at least partially regulated by L-type voltage-operated Ca⁺² channels.