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Research Article Free access | 10.1172/JCI115807

Magnesium relaxes arterial smooth muscle by decreasing intracellular Ca2+ without changing intracellular Mg2+.

E K D'Angelo, H A Singer, and C M Rembold

Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908.

Find articles by D'Angelo, E. in: PubMed | Google Scholar

Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908.

Find articles by Singer, H. in: PubMed | Google Scholar

Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908.

Find articles by Rembold, C. in: PubMed | Google Scholar

Published June 1, 1992 - More info

Published in Volume 89, Issue 6 on June 1, 1992
J Clin Invest. 1992;89(6):1988–1994. https://doi.org/10.1172/JCI115807.
© 1992 The American Society for Clinical Investigation
Published June 1, 1992 - Version history
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Abstract

Elevations in extracellular [Mg2+] ([Mg2+]o) relax vascular smooth muscle. We tested the hypothesis that elevated [Mg2+]o induces relaxation through reductions in myoplasmic [Ca2+] and myosin light chain phosphorylation without changing intracellular [Mg2+] ([Mg2+]i). Histamine stimulation of endothelium-free swine carotid medial tissues was associated with increases in both Fura 2- and aequorin-estimated myoplasmic [Ca2+], myosin phosphorylation, and force. Elevated [Mg2+]o decreased myoplasmic [Ca2+] and force to near resting values. However, elevated [Mg2+]o only transiently decreased myosin phosphorylation values: sustained [Mg2+]o-induced decreases in myoplasmic [Ca2+] and force were associated with inappropriately high myosin phosphorylation values. The elevated myosin phosphorylation during [Mg2+]o-induced relaxation was entirely on serine 19, the Ca2+/calmodulin-dependent myosin light chain kinase substrate. Myoplasmic [Mg2+] (estimated with Mag-Fura 2) did not significantly increase with elevated [Mg2+]o. These results are consistent with the hypothesis that increased [Mg2+]o induces relaxation by decreasing myoplasmic [Ca2+] without changing [Mg2+]i. These data also demonstrate dissociation of myosin phosphorylation from myoplasmic [Ca2+] and force during Mg(2+)-induced relaxation. This finding suggests the presence of a phosphorylation-independent (yet potentially Ca(2+)-dependent) mechanism for regulation of force in vascular smooth muscle.

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