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Gasser S et al.  
Free Intracellular Magnesium Remains Uninfluenced by Changes of Extracellular Magnesium in Cardiac Guinea Pig Papillary Muscle

Journal of Clinical and Basic Cardiology 2005; 8 (1-4): 29-32

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Fig. 1: Mg2+-ion-selective microelectrode Fig. 2: Mg2+

Keywords: IonKardiologiemagnesiumMyokardcardiologyion-selectivemagnesiummyocardial

It has been argued that a rise in free, unbound, intracellular Magnesium (Mg2+ i) could be beneficial during myocardial ischaemia, effecting the regulation of certain enzymes, the rectification of channels, intracellular Na+ and Ca2+, Mg2+ is a co-factor of the Na/K-ATP-ase, competes with Ca2+ at the contractile apparatus etc. However, all of these properties are confined to the intracellular site. Large trials, such as LIMIT 2, ISIS 4 and MAGIC have been conducted in order to prove a positive effect upon the outcome of patients treated with i. v. Mg during early myocardial ischaemia. In summary, the trials have failed to prove such an effect. The present study investigates the effect of extracellular Mgelevation upon intracellular concentrations of Mg2+. Here we studied Mg2+ i with Mg2+-selective microelectrode (ETH 7025) in isolated guinea pig papillary muscle. Resting Mg2+ i in 7 guinea pig papillary muscles assessed with these microelectrodes amounted to 1.06 + 0.11 mM. In 7 papillaries, varying extracellular Mg2+ levels between 0 and 8 mM produced no significant change in measured free intracellular Mg2+. Our results show that Mg2+ i remains unaffected by changes of extracellular Mg. Hence, we conclude that favourable actions of intracellular Mg2+ will not be achieved by elevating serum Mg levels using Mg infusion. These data may partially explain the negative results of ISIS 4 and MAGIC.
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