TRPM7 silencing attenuates Mg2+ influx in cardiac myoblasts, H9c2 cells

TRPM7, a member of the melastatin subfamily of transient receptor potential channels, is suggested to be a potential candidate for a physiological Mg 2+ channel. However, there is no direct evidence of Mg 2+ permeation through endogenous TRPM7. To determine the physiological roles of TRPM7 in intracellular Mg 2+ homeostasis, we measured the cytoplasmic free Mg 2+ concentration ([Mg 2+ ] i ) in TRPM7-silenced H9c2 cells. [Mg 2+ ] i was measured in a cluster of 8–10 cells using the fluorescent indicator, furaptra. TRPM7 silencing did not change [Mg 2+ ] i in Ca 2+ -free Tyrode’s solution containing 1 mM Mg 2+ . Increasing the extracellular Mg 2+ to 92.5 mM raised [Mg 2+ ] i in control cells (1.56 ± 0.19 mM) at 30 min, while this effect was significantly attenuated in TRPM7-silenced cells (1.12 ± 0.07 mM). The Mg 2+ efflux driven by Na + gradient was unaffected by TRPM7 silencing. These results suggest that TRPM7 regulates the rate of Mg 2+ influx in H9c2 cells, although cytoplasmic Mg 2+ homeostasis at basal conditions is unaffected by TRPM7 silencing.