Figure 2

pBQ and NAPQI sensitize TRPV1.Inward currents evoked by 100 nM capsaicin are constantly increased after application of 1 µM pBQ (A) or 10 µM NAPQI (B) for about 240 s even without their further presence. Proton-induced responses are also sensitized by application of pBQ (C) and NAPQI (D). Bar diagrams show means ( ± SEM) of capsaicin- (A,B) or proton-induced (C,D) inward currents (*p ≤ 0.02). pBQ (E) and NAPQI (F) shift the temperature threshold of currents induced by heat ramps (25–45 °C) to lower temperatures, shown as red dotted lines in representative recordings and as bar diagrams of temperature needed to evoke inward currents before and after treatment with pBQ (E) and NAPQI (F). The maximum heat-induced inward currents are also increased by both metabolites (pBQ *p = 0.028; NAPQI *p = 0.018). Similarly, in DRG neurons of mice pBQ sensitized capsaicin (100 nM) -induced (G) and heat induced-currents (H) and shifted temperature thresholds to lower temperatures. 50 µM HC 030031 was used throughout these experiments to block TRPA1 (*p = 0.043 (G); *p = 0.018 (H)). (I) A 100 nM capsaicin stimulus was used to identify DRG neurons expressing TRPV1. From left to right: bright field image of small DRG neurons; same neurons loaded with FURA-2AM excited at 340 nm (scale bar = 50 µm); traces of cells during a short application of 100 nM capsaicin. The capsaicin-responding neuron is marked in red and labeled with an arrow. (J) Heat-induced currents in TRPV1-expressing neurons are immediately sensitized by 10 µM NAPQI, note that NAPQI itself evokes a small inward current, while TRPA1 was blocked by HC 030031. NAPQI increased heat induced inward currents and shifted temperature thresholds of TRPV1 to lower temperatures (*p = 0.018).