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(Circulation Research. 2000;86:245.)
© 2000 American Heart Association, Inc.

Editorials

Mysteries of Magnesium Homeostasis

Elizabeth Murphy

From LMC, National Institute of Environmental Health Sciences, Research Triangle Park, NC.

Correspondence to Elizabeth Murphy, Mail Drop D2-03, Box 12233, NIEHS, Research Triangle Park, NC 27709. E-mail murphy1@niehs.nih.gov

Key Words: heart • ß-adrenergic agonist • glucose transport • insulin • mitochondria

	Introduction

 
In this issue of Circulation Research, Romani and colleagues¹ report that insulin stimulates uptake of ionized magnesium (Mg²⁺) into heart. This study is the latest in a series by Romani, Scarpa, and colleagues regarding hormone-regulated Mg²⁺ fluxes in heart and liver (References ¹ and ² and references therein). Over the past several decades, we have begun to uncover the mysteries of how cytosolic ionized calcium (Ca²⁺) is regulated and how it regulates cell function. However, the more abundant divalent cation Mg²⁺ still holds many secrets for us to unravel. Ca²⁺ signaling is facilitated by the large Ca²⁺ gradients (up to 10 000-fold) across the plasma and sarcoplasmic reticulum (SR) membranes. In contrast, only small gradients of Mg²⁺ (generally a factor of 2 or less) are reported across the plasma or intracellular membranes.^{3 4 5} In contrast to Ca²⁺ signaling, agonists do not cause large (order of magnitude) alterations in cytosolic Mg²⁺. Even upon hormonal stimulation, of heart and liver, which results in a 10% to 15% change in total cell magnesium, there is little or no change in cytosolic Mg²⁺. This lack of change in cytosolic Mg²⁺ has led many investigators to question whether Mg²⁺ is involved in hormone signaling.

	Is Intracellular Mg2+ Stable or Does It Function as an Intracellular Messenger?

 
Cytosolic Mg²⁺, which is regulated by plasma membrane and organelle transport, and by intracellular binding, is maintained far from electrochemical equilibrium. If cytosolic Mg²⁺ were at electrochemical equilibrium, it would be 188 mmol/L, assuming a membrane potential of -70 mV and extracellular Mg²⁺ of 1 mmol/L. Because the . . . [Full Text of this Article]

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