Transient receptor potential melastatin 7 ion channels regulate magnesium Homeostasis in vascular smooth muscle cells - Role of angiotensin II

Magnesium modulates vascular smooth muscle cell (VSMC) function. However, molecular mechanisms regulating VSMC Mg2+ remain unknown. Using biochemical, pharmacological, and genetic tools, the role of transient receptor potential membrane melastatin 7 (TRPM7) cation channel in VSMC Mg2+ homeostasis was evaluated. Rat, mouse, and human VSMCs were studied. Reverse transcriptase polymerase chain reaction and immunoblotting demonstrated TRPM7 presence in VSMCs ( membrane and cytosol). Angiotensin II (Ang II) and aldosterone increased TRPM7 expression. Gene silencing using small interfering RNA ( siRNA) against TRPM7, downregulated TRPM7 (mRNA and protein). Basal [Mg2+](i), measured by mag fura-2AM, was reduced in siRNA-transfected cells (0.39+/-0.01 mmol/L) versus controls (0.54+/-0.01 mmol/L; P<0.01). Extracellular Mg2+ dose-dependently increased [Mg2+](i) in control cells (E-max 0.70 +/- 0.02 mmol/L) and nonsilencing siRNA-transfected cells (E-max 0.71 +/- 0.04 mmol/L), but not in siRNA-transfected cells (E-max 0.5 +/- 0.01 mmol/L). The functional significance of TRPM7 was evaluated by assessing [Mg2+](i) and growth responses to Ang II in TRPM7 knockdown cells. Acute Ang II stimulation decreased [Mg2+](i) in control and TRPM7-deficient cells in a Na+-dependent manner. Chronic stimulation increased [Mg2+](i) in control, but not in siRNA-transfected VSMCs. Ang II-induced DNA and protein synthesis, measured by (3)[H]-thymidine and (3)[H]-leucine incorporation, respectively, were increased in control and nonsilencing cells, but not in TRPM7 knockdown VSMCs. Our data indicate that VSMCs possess membrane-associated, Ang II-, and aldosterone-regulated TRPM7 channels, which play a role in regulating basal [Mg2+](i), transmembrane Mg2+ transport and DNA and protein synthesis. These novel findings identify TRPM7 as a functionally important regulator of Mg2+ homeostasis and growth in VSMCs.