Hormonal control of Mg2+ transport in the heart.
Magnesium is abundant in the mammalian body and the second most abundant cation in cells. Because the concentration of intracellular free Mg2+ is relatively high (0.2-1 mM), Mg2+ is unlikely to act as a second messenger, like Ca2+, by rapidly changing its cytosolic concentration. But changes in Mg2+ do have profound effects on cellular metabolism, structure and bioenergetics. Key enzymes or metabolic pathways, mitochondrial ion transport, Ca2+ channel activities in the plasma membrane and intracellular organelles, ATP-requiring reactions, and structural properties of cells and nucleic acids are modified by changes in Mg2+ concentration. Yet, although some information is available from giant cells and bacteria, little is known about the regulation of intracellular Mg2+ in mammalian cells. Here we report a new transport mechanism for Mg2+ across the sarcolemma of cardiac cells in both intact hearts and dissociated myocytes. We show that noradrenaline, through beta-adrenergic stimulation and increase of cyclic AMP, stimulates a large efflux of Mg2+ from cardiac cells. This transport is of major dimensions and can move up to 20% of total cellular Mg2+ within a few minutes.
Romani
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Department of Physiology and Biophysics, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106.
Scarpa
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D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D000242:Cyclic AMP / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006706:Homeostasis; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D012508:Sarcolemma / Q000378:metabolism; D013054:Spectrophotometry, Atomic
D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D011433:Propranolol; D000242:Cyclic AMP; D008274:Magnesium; D009638:Norepinephrine