Inhibition of TRPM2 cation channels by N-(p-amylcinnamoyl)anthranilic acid

1 TRPM2 is a Ca2+-permeable nonselective cation channel activated by intracellular ADP-ribose (ADPR) and by hydrogen peroxide (H2O2). We investigated the modulation of TRPM2 activity by N-(p-amylcinnamoyl)anthranilic acid (ACA). ACA has previously been reported to inhibit phospholipase A(2) (PLA(2)). 2 Using patch-clamp and calcium-imaging techniques, we show that extracellular application of 20 mu m ACA completely blocked ADPR-induced whole-cell currents and H2O2-induced Ca2(+) signals (IC50 = 1.7 mu m) in HEK293 cells transfected with human TRPM2. Two other PLA2 inhibitors, p-bromophenacyl bromide (BPB; 100 mu m) and arachidonyl trifluoromethyl ketone (20 mu m), had no significant effect on ADPR-stimulated TRPM2 activity. 3 Inhibition of TRPM2 whole-cell currents by ACA was voltage independent and accelerated at decreased pH. ACA was ineffective when applied intracellularly. The single-channel conductance was not changed during ACA treatment, suggesting a reduction of TRPM2 open probability by modulating channel gating. 4 ACA (20 mu m) also blocked currents through human TRPM8 and TRPC6 expressed in HEK293 cells, while BPB (100 mu m) was ineffective. TRPC6-mediated currents (IC50=2.3 mu m) and TRPM8-induced Ca2+ signals (IC50 = 3.9 mu m) were blocked in a concentration-dependent manner. 5 ADPR-induced currents in human U937 cells, endogeneously expressing TRPM2 protein, were fully suppressed by 20 mu m ACA. 6 Our data indicate that ACA modulates the activity of different TRP channels independent of PLA2 inhibition. Owing to its high potency and efficacy ACA can serve, in combination with other blockers, as a useful tool for studying the unknown function of TRPM2 in native cells.