Figure 4. MEL and IIK7 inhibit forskolin-induced cAMP production only in the presence of MT_1/2h. A: Effect of melatonin (MEL) on forskolin-induced cAMP production in 661W cells. B: IIK7 effect on forskolin-induced cAMP production in 661W cells. C: Effect of luzindole (LUZ) on the effect of MEL on forskolin-induced cAMP production. D: Effect of MEL on forskolin-cAMP in 661W-melatonin receptor type 2 (MT₂)^−/− cells. In all the cases, results (n = 6) are shown as mean ± standard error of the mean (SEM). Asterisks indicate statistically significant differences compared to the control group with one-way ANOVA (Student–Newman–Keuls (SNK) post-hoc test; p<0.05).