NMR Measurement of Intracellular Free Magnesium Ions in Living Cells

Abstract

³¹P NMR permits a noninvasive measurement of the extent of Mg ²⁺-complexation of ATP and the concentration of free magnesium from an accurate measurement of the Mg²⁺-dependent chemical shift difference between the αP and βP resonances of intracellular ATP. The technique has been used to monitor intra-erythrocyte free Mg²⁺ during blood storage at 4^°C in standard citrate preservation media. The data indicated a marked decrease in the extent of Mg²⁺-complexation of ATP, and in the level of intracellular free Mg²⁺, during the shelf-life of blood stored in citrate media. Mg²⁺-saturated and Mg²⁺-depleted human erythrocytes exhibited the intra-erythrocyte ATP resonances at relative chemical shifts that were indistinguishable from those observed in noncellular MgATP and ATP controls, respectively. In another study, changes in intracellular free Mg ²⁺ were observed in erythrocytes of patients with essential hypertension. Untreated hypertensive individuals consistently demonstrated lower levels of intra-erythrocyte free Mg²⁺ (192^±8 uM) than either normotensive (261^±10 uM) or hypertensive subjects whose blood pressure had been normalized on therapy (237^±8 uM). For all subjects, significant relationship existed between intra-erythrocyte free Mg²⁺ and diastolic as well as systolic blood pressure. It was concluded that significant depletion of intra-erythrocyte free Mg²⁺ is apparent in erythrocytes of subjects with essential hypertension. The observed linear relationship of free Mg²⁺ with the height of the blood pressure suggested that abnormalities of intracellular Mg²⁺ metabolism may contribute to the pathophysiology of human essential hypertension.