Free magnesium concentration in isolated rabbit hearts subjected to high dose isoproterenol infusion: a ³¹P NMR study

Abstract

The hypothesis of magnesium deficiency in isoproterenol (ISO) induced myocardial injury has been investigated by 31P nuclear magnetic resonance spectroscopy. High energy phosphate concentrations, pHi, and intracellular free magnesium concentration ([Mg2+]i) were measured in isolated rabbit hearts perfused at constant flow and subjected to 10(-6)M isoproterenol during 30 min. Recent calibrations were used for [Mg2+]i measurements, and uncertainties on [Mg2+]i estimated values were calculated. During isoproterenol infusion, pHi, [PCr], and [ATP] decreased, while [P(i)] increased. When it was stopped, [PCr] completely repleted, whereas only a partial restoration was observed for pHi and [P(i)]. A rise of end-diastolic pressure and perfusion pressure expressed a contracture, concomitant with a lack of [ATP] recovery, which remained at 59 +/- 13% of the rest value. These results establish that 10(-6) M isoproterenol caused severe myocardial injury. [Mg2+]i increased from 0.70 mM at rest to 0.88 mM at the end of the isoproterenol period. Considering the estimated uncertainties on the [Mg2+]i values, this increase was not significant. After isoproterenol infusion, [Mg2+]i progressively decreased to reach 0.72 mM at 45 min recovery. It is concluded that isoproterenol myocardial toxicity may not be related to [Mg2+]i deficiency.

Renal handling of magnesium in fish: from whole animal to brush border membrane vesicles

“…There is good agreement that most intracellular Mg is bound leaving free, ionized Mg in the cytoplasm at concentrations in the vicinity of 1 mM (34,35,36). The concentration of intracellular free Mg must be well regulated in view of the diverse roles of Mg that range from stabilizing structures such as DNA and the cytoskeleton, to activating enzymes, to modulating membrane channels and G-proteins and to antagonizing the actions of Ca (37).…”