Regulation of magnesium uptake and release in the heart and in isolated ventricular myocytes.
Perfused rat hearts release or accumulate approximately 10% of total Mg2+ content when stimulated with norepinephrine (NE) or carbachol, respectively. Collagenase-dispersed rat ventricular myocytes increase or decrease total cell Mg2+ by 1 mM within 5 minutes when stimulated with these same transmitters. Measurements of Mg2+ transport using 28Mg or atomic absorbance spectrophotometry indicate that the rate and the extent of both stimulated Mg2+ efflux and influx are independent of the concentration of extracellular Mg2+ (0 to 1.2 mM). Mg2+ release induced by NE is rapidly reversed by the addition of carbachol, and Mg2+ uptake induced by carbachol is reversed by NE. Decreasing extracellular Na+ or Ca2+ decreases or abolishes Mg2+ efflux from myocytes. Cd2+ or other Ca2+ channel blockers also inhibit Mg2+ efflux in the presence of a physiological concentration of extracellular Ca2+. Replacement of extracellular Ca2+ with Sr2+ or with Mn2+ decreases or abolishes both stimulated efflux and influx of Mg2+. Redistribution of 85Sr in myocytes and in the supernatant indicates that under those conditions Sr2+ is released or accumulated by NE or carbachol in a manner similar to that of Mg2+. Hence, at least in the case of Sr2+, the inhibition of Mg2+ fluxes can be explained by the transport of Sr2+ rather than Mg2+ through the transport(s) systems. By contrast, replacement of extracellular Ca2+ with Ba2+ inhibits stimulated Mg2+ uptake but not Mg2+ release. These results indicate that cardiac myocytes have a major pool of Mg2+ that can be rapidly mobilized upon hormonal stimulation. The net uptake and release of Mg2+ are quantitatively similar and appear to be independent of the extracellular Mg2+ concentrations but are affected, to various degrees, by the presence of other cellular or extracellular cations.
Department of Physiology and Biophysics, Case Western Reserve University, School of Medicine, Cleveland, OH 44106.
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Romani
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Marfella
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Scarpa
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002217:Carbachol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000502:physiology; D013324:Strontium / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology
D002104:Cadmium; D002217:Carbachol; D012964:Sodium; D014700:Verapamil; D008274:Magnesium; D009543:Nifedipine; D002118:Calcium; D009638:Norepinephrine; D013324:Strontium