Evidence that the FSH receptor itself is not a calcium channel

FSH has been shown to stimulate the uptake of calcium in cultured rat Sertoli cells, resulting in an increase in cytosolic calcium concentrations. One possibility which has been put forth is that the FSH receptor per se may act as a calcium channel. This is all the more tantalizing given the proposed structure of this receptor which, like all other G protein-coupled receptors, is thought to have the putative transmembrane helices forming a bundle-like structure in the plasma membrane. To test whether the FSH receptor could function as a calcium channel, we performed whole-cell voltage clamp experiments on 293 and 293F(wt1) cells, which are a clonal line of 293 cells expressing high levels of rat FSH receptors. The 293 cells, which do not express FSH receptors, were found to lack any detectable inward calcium currents, and therefore, serve as an excellent model for transfecting with potential calcium conducting FSH receptors. When the 293F(wt1) cells were then tested, no inward calcium currents could be detected in either control or FSH-stimulated cells. These results suggest that the FSH receptor itself is not a calcium channel and, therefore, FSH must be stimulating endogenous calcium channels in rat Sertoli cell plasma membranes.