Synergistic regulation of endogenous TRPM2 channels by adenine dinucleotides in primary human neutrophils

The Ca2+-permeable TRPM2 channel is a dual function protein that is activated by intracellular ADPR through its enzymatic pyrophosphatase domain with Ca2+ acting as a co-factor. Other TRPM2 regulators include cADPR, NAADP and H2O2, which synergize with ADPR to potentiate TRPM2 activation. Although TRPM2 has been thoroughly characterized in overexpression or cell-line systems, little is known about the features of TRPM2 in primary cells. We here characterize the regulation of TRPM2 activation in human neutrophils and report that ADPR activates TRPM2 with an effective half-maximal concentration (EC50) of 1 μM. Potentiation by Ca2+ is dose-dependent with an EC50 of 300 nM. Both cADPR and NAADP activate TRPM2, albeit with lower efficacy than in the presence of subthreshold levels of ADPR (100 nM), which significantly shifts the EC50 for cADPR from 44 to 3 μM and for NAADP from 95 to 1 μM. TRPM2 activation by ADPR can be suppressed by AMP with an IC50 of 10 μM and cADPR-induced activation can be blocked by 8-Bromo-cADPR. We further show that 100 μM H2O2 enables subthreshold concentrations of ADPR (100 nM) to activate TRPM2. We conclude that agonistic and antagonistic characteristics of TRPM2 as seen in overexpression systems are largely compatible with the functional properties of TRPM2 currents measured in human neutrophils, but the potencies of agonists in primary cells are significantly higher.