Magnesium regulates intracellular free ionized calcium concentration and cell geometry in vascular smooth muscle cells.
Regulatory effects of extracellular magnesium ions ([Mg2+]o) on intracellular free ionized calcium ([Ca2+]i) were studied in cultured vascular smooth muscle cells (VSMCs) from rat aorta by use of the fluorescent indicator fura-2 and digital imaging microscopy. With normal Mg2+ (1.2 mM)-containing incubation media, [Ca2+]i in VSMCs was 93.6 +/- 7.93 nM with a heterogeneous cellular distribution. Lowering [Mg2+]o to 0 mM or 0.3 mM (the lowest physiological range) resulted in 5.8-fold (579.5 +/- 39.99 nM) and 3.5-fold (348.0 +/- 31.52 nM) increments of [Ca2+]i, respectively, without influencing the cellular distribution of [Ca2+]i. Surprisingly, [Mg2+]o withdrawal induced changes of cell geometry in many VSMCs, i.e., the cells rounded up. However, elevation of [Mg2+]o up to 4.8 mM only induced slight decrements of [Ca2+]i (mean = 72.0 +/- 4.55 nM). The large increment of [Ca2+]i induced by [Mg2+]o withdrawal was totally inhibited when [Ca2+]o was removed. The data suggest that: (1) [Mg2+]o regulates the level of [Ca2+]i in rat aortic smooth muscle cells, and (2) [Mg2+] acts as an important regulatory ion by modulating cell shapes in cultured VSMc and their metabolism to control vascular contractile activities.
Zhang
A
A
Department of Physiology, State University of New York, Brooklyn.
Cheng
T P
TP
Altura
B M
BM
D000818:Animals; D001011:Aorta / Q000166:cytology; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D066298:In Vitro Techniques; D008274:Magnesium / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology*; D051381:Rats
D008274:Magnesium; D002118:Calcium