mTRPM7 is inhibited by oxidative stress that is induced by H₂O₂ in an [Mg²⁺]_i-dependent manner. (A) Effect of H₂O₂ (500 µM) on mTRPM7 current at +80 mV in the absence (open circles; n = 14) or the presence of 0.2 mM [Mg²⁺]_i (closed circles; n = 8). Under the whole-cell clamp mode, ramp command pulses from −100 to +100 V (1-s duration) were applied every 10 s. Each symbol represents the mean ± SEM (vertical bar). (B) Representative I-V relationship of mTRPM7-wt current recorded in the presence of 0.2 mM [Mg²⁺]_i before (black line) or 4 min after (red line) the application of H₂O₂ (500 µM). (C) Representative I-V relationship of mTRPM7-wt current recorded in the absence of intracellular Mg²⁺ before (black line) or 4 min after (red line) the application of H₂O₂ (500 µM). (D) [Mg²⁺]_i-dependent inhibition of mTRPM7 current under control (black circles) and H₂O₂-treated (red circles) conditions. The data are presented as a relative current to the mean current that was recorded at 2 min after break-in (i.e., just before application of H₂O₂) in the absence of intracellular Mg²⁺. Under control conditions (just before H₂O₂ application), the current was inhibited by intracellular free Mg²⁺ with an IC₅₀₍₁₎ of 5.6 µM and an IC₅₀₍₂₎ of 558 µM (black line). After H₂O₂ treatment for 4 min, the current was inhibited by intracellular free Mg²⁺ with IC₅₀ at 3.4 µM (red line). Each symbol represents the mean ± SEM (vertical bar) of 18, 10, 13, 7, 8, 12, 22, 4, and 8 observations in the absence or presence of 2.8 µM, 7.4 µM, 20.9 µM, 0.2 mM, 0.5 mM, 1 mM, 2 mM, and 5 mM [Mg²⁺]_i, respectively. (E) A Mg²⁺-insensitive mutant, mTRPM7-S1107E, was not inhibited by H₂O₂ (500 µM) in the absence (open squares; n = 16) or the presence of 0.2 mM [Mg²⁺]_i (closed squares; n = 13). Each symbol represents the mean ± SEM (vertical bar). (F) Mean mTRPM7-S1107E current density did not differ in the absence (open bars) or presence (closed bars) of H₂O₂. Each bar represents the mean ± SEM of 15, 14, 8, and 8 observations in the absence or presence of 0.2, 0.5, and 1 mM [Mg²⁺]_i, respectively. (G) A caspase cleavage–resistant mutant mTRPM7-D1510A was inhibited by H₂O₂ (500 µM) in the presence of 0.2 mM [Mg²⁺]_i (closed triangles). Each symbol represents the mean ± SEM (vertical bar) of six recordings. (H) The inhibitory effect of NMM (100 µM) on the mTRPM7 current in the presence of 0.2 mM [Mg²⁺]_i (closed circles). Each symbol represents the mean ± SEM (vertical bar) of five recordings. (I) NMM (100 µM) inhibited mTRPM7 current in the presence of 0.2 mM [Mg²⁺]_i (n = 9), but not in the absence of intracellular Mg²⁺ (n = 4). Each bar represents the mean ± SEM (vertical bar). *, P = 0.00035 by paired t test versus control.