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 ([Mg2+](i)) in TRPM7-silenced H9c2 cells. [Mg2+](i)was measured in a cluster of 8-10 cells using the fluorescent indicator, furaptra. TRPM7 silencing did not change [Mg2+](i)in Ca2+-free Tyrode's solution containing 1 mM Mg2+. Increasing the extracellular Mg(2+)to 92.5 mM raised [Mg2+](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.