Re-estimation of the intracellular free magnesium concentration using ³¹P-NMR

Abstract

Intracellular Mg²⁺ is known to affect many intracellular enzymes and other important cellular processes. In ³¹P-NMR spectrum, the observed chemical shifts of the ATP peaks indicate the ratio of metal-free to total ATP. Thereby, the intracellular Mg²⁺ concentration ([Mg²⁺]_i) can be estimated from the chemical shifts of ATP peaks assuming the dissociation constant of MgATP (K_D^"MgATP"). pH is known to affect the K_D^"MgATP". McGuigan's group have shown that K_D^"MgATP" at 25 and 37°C are described as quadratic functions of pH (Zhang et al. Anal Biochem 251, 246-250, 1997). In this presentation, we estimate [Mg²⁺]_i from the chemical shifts of intracellular ATP, using the formula modified for our experimental conditions. We will communicate the re-evaluated resting [Mg²⁺]_i in smooth and cardiac muscles, and also show various modulations of [Mg²⁺]_i caused by changing ionic substitutions and applying important hormones and drugs. [Jpn J Physiol 54 Suppl:S36 (2004)]