Figure 5. AMPCPR cannot be hydrolyzed by nvTRPM2, but still activates the channel.

(A) Nucleoside diphosphohydrolase rates of WT nvNUDT9-H (nvWT), reported as P_i (in μM) released by co-applied alkaline phosphatase (AP), in sample mixtures containing, as indicated, AP (2–3 U), ADPR (100 μM), AMPCPR (100 μM), AMP (100 μM), nvNUDT9-H (1 or 10 nM), and incubated for 5 min at room temperature in the presence of 16 mM Mg²⁺, pH=8.5. Data are shown as mean ± SEM of 3 experiments. (B) Macroscopic nvTRPM2 currents activated by repeated exposures to (100 μM) ADPR (purple bars) or various concentrations of AMPCPR (blue bars) in the presence of 125 μM Ca²⁺ (black bar). Colored solid lines are fitted exponentials with time constants (in ms) indicated. (C) Fractional current activation by indicated concentrations of AMPCPR (blue bars; mean ± SEM from 4 to 7 patches), normalized to the current elicited in the same patch by 100 μM ADPR (purple bar). (D) Average macroscopic current decay time constants (mean ± SEM from 5 patches) following removal of the activating nucleotide.