Fig. 3. Reduced D₂ receptor-mediated plasma membrane Ca²⁺ channel activity after co-expression with sG_i2 demonstrates the reduced D₂ receptor density at cell surface. (A,B) Typical intracellular Ca²⁺ transient in a single BHK cell expressing (A) D2S and (B) D2L receptor, after application of 15 µM raclopride, a D₂ antagonist. This activity was significantly reduced in cells when sG_i2 was co-expressed. (C) Summary of the results from experiments using NG108-15 cells. Co-expression of sG_i2 with either D_2L or D_2S produced a 30-35% decrease in Ca²⁺ transients, similar to receptor binding results shown in Fig. 1. This activity was associated with D₂ and not to D₁ receptors. In addition, expression of G_i2 instead of sG_i2 did not show any change. F/F₀ represents the change in fluorescence intensity over baseline (see Materials and Methods). ^*P<0.05, significant change from control. Values are representative of six different experiments.