Fig. 3.

CCK-58 and CCK-8 disrupt CCK₁ receptor oligomerization. Shown are bioluminescence resonance energy transfer (BRET) ratios obtained from COS cells coexpressing Renilla luciferase (Rlu)-and YFP-tagged human CCK₁ receptors (HCCKAR). Cells expressing the CCK receptor constructs were incubated with increasing concentrations of either CCK-8 or CCK-58 prior to measurement of the BRET signals. Concentration-dependent decreases in the BRET signals were observed after stimulation with each of the peptides. The shaded area represents the background BRET ratio that can be measured upon expression of structurally unrelated receptors on the cell surface or upon expression of a donor-acceptor pair with one in the plasma membrane and the other in the cytosol. Signals above this are considered to be significant. Data represent means ± SE of 4 independent experiments. *P < 0.05, **P < 0.01 compared with BRET signals obtained without exposure to CCK peptides.