Stability of free Mg2+ concentration and increased concentration of free Ca2+ in vascular smooth muscle cells during dietary magnesium deficiency in rat.

Intracellular free calcium and magnesium ion concentrations ([Ca2+]i and [Mg2+]i respectively) were estimated in thoracic aorta smooth muscle strips isolated from magnesium-deficient and control rats using fura-2/AM and mag-fura-2/AM, respectively. Adult male Wistar rats were fed a magnesium-deficient diet (10 mg Mg/kg diet) or a control diet (700 mg Mg/kg diet) for 30 days. Plasma magnesium level in magnesium-deficient rats was half of that in control rats at 30th day. Therefore, thoracic aorta strips, denuded of endothelium, were loaded with fura-2/AM or mag-fura-2/AM in the presence of 0.5 or 1.0 mM Mg2+, and [Ca2+]i or [Mg2+]i was measured under the same Mg2+ conditions. The [Ca2+]i in the aorta strips isolated from magnesium-deficient rats in the presence of 0.5 mM Mg2+ (254.9 +/- 13.1 nM) was approximately three times greater than in those from control rats in the presence of 1.0 mM Mg2+ (86.5 +/- 9.2 nM). The [Mg2+]i was not significantly different between the two groups at either Mg2+ level. The muscle tension and [Ca2+]i increased after [Mg2+]o was exchanged from 1.0 to 0.5 mM; however, [Mg2+]i showed no change. The total calcium content increased and total magnesium content decreased in thoracic aorta strips isolated from magnesium-deficient rats. These results suggest that [Mg2+]i is stable, but that [Ca2+]i increases in vascular smooth muscle cells of thoracic aortas isolated from dietary magnesium-deficient rats.