TABLE 3

Competition of melatonin, luzindole, and cluster 1 carbamate insecticides for 2-[¹²⁵I]-iodomelatonin binding to hMT₁ and hMT₂ expressed in CHO cells without and with G protein inactivation

Competition for 2-[¹²⁵I]-iodomelatonin (75 pM) binding of melatonin, luzindole, and cluster 1 carbamate insecticides were performed in the absence (active buffer) or presence (resting buffer) of 100 μM GTP, 1 mM EDTA.Na₂, and 150 mM NaCl at 25°C for 1 hour. pKi values were calculated from IC₅₀ values obtained from competition curves (see Supplemental Fig. 4) by the method of Cheng and Prusoff (1973). Shown are mean pKi values and 95% confidence intervals of at least three independent determinations. pK_is obtained in active and resting buffer were analyzed for differences using two-tailed paired t tests. Decreases (ΔpK_i = pK_iGTP − pK_iControl; negative ΔpK_i and >20% melatonin effect) of affinity in resting buffer indicate agonist apparent efficacy, whereas no change or increases in affinity (<20% melatonin effect or positive ΔpK_i) indicate antagonist or inverse agonist apparent efficacy, respectively.