Purified pyridine dinucleotides do not compete activation of TRPM2 channels by ADPR. (A–C) Macroscopic T5L-TRPM2 currents elicited by cytosolic application of saturating Ca²⁺ (black bars) and either 32 or 1 µM ADPR (dark blue bars) alone, or a mixture of 1 µM ADPR with a high concentration of NUDT9-treated, filtered (“purified”) NAD (A, green bar), NAAD (B, blue bar), or NAADP (C, purple bar). (D) Fractional current activation by 1 µM ADPR alone (dark blue) or in combination with indicated concentrations of NUDT9-treated, filtered NAD (green), NAAD (blue), and NAADP (purple). Currents were normalized to those measured in 32 µM ADPR. Error bars represent mean ± SEM.