Application of the Accurate Assessment of Intracellular Magnesium and pH from the 31P Shifts of ATP to Cerebral Hypoxia‐Ischemia in Neonatal Rat

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Abstract
The authors present a high field in vivo demonstration of our 2‐dimensional calibration methods for determining magnesium ion concentration ([Mg]), under conditions of fluctuating pH, from the three 31P NMR chemical shift differences of ATP. The effect of 3 h of hypoxic‐ischemic insult (HI) on intracellular brain [Mg] was evaluated by using a well established 7‐day‐old rat model of cerebral HI. During the final hour of HI, there was a significant increase (P < 0.001) in free magnesium as well as in the ratio of total [Mg]/[ATP]. The normal, HI, and early (1–2 h) recovery values of free [Mg] were 0.336 ± 0.015, 0.519 ± 0.104, and 0.337 ± 0.071 mM, respectively. These results are consistent with the temporal changes in [ATP]. Our assessment of [Mg] and pH for this high error measurement is general for most in vivo applications and may be routinely implemented.