Reduction of intracellular Mg caused by reactive oxygen species in rat ventricular myocytes.

The concentration of intracellular free Mg ([Mg]) should be maintained strictly for the regulation of cellular functions. Since reactive oxygen species (ROS) are liable to increase in various pathological conditions and induce cellular damage, we investigated whether ROS affect intracellular Mg homeostasis. We measured [Mg] in ventricular myocytes from Wistar rats using the fluorescent indicator, mag-fura-2. The administration of hydrogen peroxide (HO) decreased [Mg] in Ca-free Tyrode's solution. Intracellular free Mg was also reduced by endogenous ROS as generated by pyocyanin, which was inhibited by pretreatment with -acetyl cysteine (NAC). The rate of change in [Mg] by 500 μM HO in 5 min (on average, -0.61 μM/s) was independent of extracellular Na, and intra- and extracellular Mg concentrations. When extracellular Ca was present, the rate of Mg decrease was significantly reduced, on average, by ∼60%. The half-maximal effective concentration of HO on the Mg decrease was estimated to be between 400 and 425 μM. The Mg decrease by HO in the absence of Na was inhibited by 200 μM imipramine, a known inhibitor of Na/Mg exchange. We perfused rat hearts with the Ca-free Tyrode's solution containing HO (500 μM, 5 min) on the Langendorff apparatus, HO stimulation increased Mg concentration in the perfusate, suggesting the HO-induced decrease in [Mg] was caused by Mg extrusion. Collectively, these results suggest the existence of a Na-independent Mg efflux system activated by ROS in cardiomyocytes. The lower [Mg] may in part be attributed to ROS-mediated cardiac dysfunction.