EC50: 0.3 nM (motilin receptor, Chinese hamster ovary cell)
Ki: 2.3 nM (motilin receptor, Chinese hamster ovary cell)

[Bpa ¹ ,Ile ¹³ ]motilin is a full agonist at the motilin receptor that increases intracellular calcium in a concentration-dependent manner (EC ₅₀ = 1.5 ± 0.4 nM). Motilin binds with high affinity (IC ₅₀ 0.7± 0.2 nM) to receptors on smooth muscle cells. Motilin selectively activates G(q) and G(13), stimulates G alpha(q)-dependent phosphoinositide (PI) hydrolysis and 1,4,5-trisphosphate (IP(3))-dependent Ca ²⁺ release, and increases cytosolic free Ca ²⁺ . Motilin induces a biphasic, concentration-dependent contraction (EC ₅₀ = 1.0 +/- 0.2 nM), consisting of an initial peak followed by a sustained contraction.