Fig. 5.

Direct measurement of Na⁺ effect on GPCR signaling. (A) Exchange of K⁺ to Na⁺ leads to reduced basal activity, but maintains agonist-induced signal (Costa et al., 1990). (B) Addition of Na⁺ dramatically enhances differential between agonists and antagonists of G-protein signaling in MOR (Selley et al., 2000). (C) Addition of Na⁺ reduces basal activity of DRD4 (Wang et al., 2017). This figure reproduced with permission.