Activation of macroscopic TRPM2 currents requires micromolar [Ca²⁺]_i. (A) Macroscopic TRPM2 current from an inside-out patch superfused with 32 µM ADPR and various test [Ca²⁺]_i, bracketed by exposures to 125 µM Ca²⁺ (bars). Pipette [Ca²⁺] was ∼4 µM. (B) Mean currents in test [Ca²⁺]_i, normalized to the mean of the currents in bracketing 125-µM Ca²⁺ segments, were plotted against [Ca²⁺]_i and fitted to the Hill equation. Pipette [Ca²⁺] was either ∼4 µM (closed circles and solid fit line) or 1 mM (open circles and dashed fit line). Data are represented as mean ± SEM.