Nicotinic acid and 2-APB synergistically activate TRPV1. (A) Molecular structure of 2-APB (top) and representative currents elicited by 65 mM nicotinic acid and 180 μM 2-APB independently or jointly (bottom). (B) Additive effect of nicotinic acid on 2-APB-induced channel activation shown as representative recording (left) and statistical analysis (right, n = 11. ***, p < 0.001). (C) 2-APB dose-response curves with (green) or without (grey) 65 mM nicotinic acid. (D) Nicotinic acid dose-response curves with (green) or without (grey) 180 μM 2-APB. Superimposed are fits of a Hill equation with the following parameters (EC50 and slope factor): 2-APB without nicotinic acid, 157.2 ± 17.9 μM and 2.35 ± 0.15; 2-APB with nicotinic acid, 66.28 ± 7.69 μM and 2.24 ± 0.31; Nicotinic acid without 2-APB, as in Fig. 2D; Nicotinic acid with 2-APB, 35.81 ± 2.7 mM and 1.98 ± 0.29. n = 4 each.