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

2. INTRODUCTION

Although calcium ions (Ca²⁺) act as important intracellular "second messengers" in regulation of endothelial cell functions (1), the possible role of ionized magnesium [Mg²⁺] as a physiological regulator in these cells has not received experimental attention until very recently. Evidence has accumulated to suggest that extracellular Mg²⁺ concentrations ([Mg²⁺]_o) can also play critical roles in various activities of endothelial cells. Changes of [Mg²⁺]_o have been found to influence synthesis/release of endothelial-derived relaxation factors (EDRFs) (2,3), intracellar Ca²⁺ concentrations ((Ca²⁺)_i) and intracellular Ca²⁺ release (4), activities of cation channels (5,6), Ca²⁺-Na⁺ exchange (7), membrane potential (8), and uptake and metabolism of low density lipoprotein (9) and permeability to water and albumin (10), as well as proliferation and migration of endothelial cells (11). In addition, experimental deficiency in [Mg²⁺]_o has been reported to enhance free radical-induced cytotoxicity in endothelial cells (12).

Despite these important known cellular attributes and functions, underlying mechanism(s) of the actions of [Mg²⁺]_o in endothelial cells are not fully understood. One possibilty is that regulatory effects of [Mg²⁺]_o may be mediated via rapid changes in intracellular Mg²⁺ concentration [Mg²⁺]_i. Recently, evidence has been provided that [Mg²⁺]_o may be regulatory cations in several types of eukaryotic cells, including vascular cells (13-16). [Mg²⁺]_i is known to be a cofactor for more than 325 enzymes and signal-transduction proteins, and it regulates bioenergetics and ion transport (for reviews, see 17-19). It would, thus, be of importance to know whether or not changes in [Mg²⁺]_o can alter rapidly [Mg²⁺]_i in endothelial cells. The present communication reports for the first time the basal level of [Mg²⁺]_i and effects of [Mg²⁺]_o on regulation of [Mg²⁺]_i in human vascular endothelial cells.