Aimin Zhang¹, Bella T. Altura^2,3 and Burton M. Altura^1,2,3

Departments of ¹Physiology and ²Medicine, and ³The Center for Cardiovascular and Muscle Research, State University of New York, Health Science Center at Brooklyn, NY 11203

Received 5/15/97; Accepted 5/21/97; On-line 6/1/97

1. ABSTRACT

Extracellular magnesium ions [Mg²⁺]_o are known to regulate functions of endothelial cells, but whether [Mg²⁺]_o can alter intracellular free ionized magnesium [Mg²⁺]_i in these cells remains unknown. The present studies, using digital imaging microscopy and the Mg²⁺ fluorescent probe, mag-fura-2, determined effects of elevation of [Mg²⁺]_o on [Mg²⁺]_i in cultured human aortic endothelial cells. With normal Mg²⁺(1.2 mM)-containing incubation media, [Mg²⁺]_i was 0.51±0.04 mM with a heterogeneous distribution. The ratio of [Mg²⁺]_i/[Mg²⁺]_o was 0.52±0.07. Elevation of [Mg²⁺]_o up to 4.8 mM increased [Mg²⁺]_i to 0.80±0.07 mM in 2-10 min and lowered the ratio of [Mg²⁺]_i/[Mg²⁺]_o to 0.16±0.02. Irrespective of the observed increments of [Mg²⁺]_i, a subcellular heterogeneous distribution of [Mg²⁺]_i was always evident in all cells tested. Our results suggest that [Mg²⁺]_o can regulate [Mg²⁺]_i more rapidly than heretofore believed, supporting the hypothesis that extracellular Mg²⁺ can exert regulatory effects on endothelial cell functions and probably act as extracellular regulatory cations.