Na+ modulates the affinity of the lutropin/choriogonadotropin receptor

The studies presented herein were designed to assess the effects of Na+ on the affinity of the lutropin/choriogonadotropin (LH/CG) receptor. We performed competition binding experiments in buffers containing NaCl or an isosmolar concentration of an appropriate Na+ substitute. The results presented show that Na+ decreases the affinity of LH, but not that of CG, in intact cells and membranes. In detergent-solubilized receptors, however, the affinity of LH is higher than that of CG and is not influenced by Na+. In addition, we show that Na+ does not affect the number of LH/CG receptors.