New ionic targets of 3,3′,5′-triiodothyronine at the plasma membrane of rat Sertoli cells

The functions of Sertoli cells, which structurally and functionally support ongoing spermatogenesis, are effectively modulated by thyroid hormones, amongst other molecules. We investigated the mechanism of action of rT(3) on calcium (Ca-45(2+)) uptake in Sertoli cells by means of in vitro acute incubation. In addition, we performed electrophysiological recordings of potassium efflux in order to understand the cell repolarization, coupled to the calcium uptake triggered by rT(3). Our results indicate that rT(3) induces nongenomic responses, as a rapid activation of whole-cell potassium currents in response to rT(3) occurred in < 5 min in Sertoli cells. In addition, the rT(3) metabolite, T-2, also exerted a rapid effect on calcium uptake in immature rat testis and in Sertoli cells. rT(3) also modulated calcium uptake, which occurred within seconds via the action of selective ionic channels and the Na+/K+ ATPase pump. The rapid response of rT(3) is essentially triggered by calcium uptake and cell repolarization, which appear to mediate the secretory functions of Sertoli cells.