TRPM7 silencing attenuates Mg 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 channel. However, there is no direct evidence of Mg permeation through endogenous TRPM7. To determine the physiological roles of TRPM7 in intracellular Mg homeostasis, we measured the cytoplasmic free Mg concentration ([Mg]) in TRPM7-silenced H9c2 cells. [Mg] was measured in a cluster of 8-10 cells using the fluorescent indicator, furaptra. TRPM7 silencing did not change [Mg] in Ca-free Tyrode's solution containing 1 mM Mg. Increasing the extracellular Mg to 92.5 mM raised [Mg] 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 efflux driven by Na gradient was unaffected by TRPM7 silencing. These results suggest that TRPM7 regulates the rate of Mg influx in H9c2 cells, although cytoplasmic Mg homeostasis at basal conditions is unaffected by TRPM7 silencing.