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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1997;17:3356-3361.)
© 1997 American Heart Association, Inc.

Articles

Differential Effects of Extracellular Mg²⁺ on Thrombin-Induced and Capacitative Ca²⁺ Entry in Human Coronary Arterial Endothelial Cells

Mitsuisa Yoshimura; Tetsuya Oshima; Hideo Matsuura; Toshiaki Inoue; Masayuki Kambe; ; Goro Kajiyama

From the First Department of Internal Medicine (M.Y., H.M., T.I., G.K.) and the Department of Clinical Laboratory Medicine (T.O., M.K.), Hiroshima University School of Medicine, Hiroshima, Japan.

Correspondence to Mitsuisa Yoshimura. MD, First Department of Internal Medicine, Hiroshima University School of Medicine, 1-2-3 Kasumi, Minami-ku, Hiroshima 734, Japan. E-mail myoshimu{at}mcai.med.hiroshima-u.ac.jp

Abstract Receptor-mediated and capacitative Ca²⁺ entry are the primary Ca²⁺ entry pathways in endothelial cells (ECs). The mechanisms for Ca²⁺ entry via these pathways have not been fully elucidated. In this study, the effect of low and high external Mg²⁺ concentrations on these Ca²⁺ entry pathways was examined in human coronary arterial ECs. External Mg²⁺ concentration did not affect cytosolic free Mg²⁺ concentration. After exposure to thrombin in Ca²⁺-free medium, addition of Ca²⁺ to the medium caused a rise in cytosolic free Ca²⁺ concentration ([Ca²⁺]i), indicating thrombin-induced Ca²⁺ influx. Thrombin-induced Ca²⁺ influx was inhibited by not only low but also high external Mg²⁺ concentrations. After depletion of endoplasmic Ca²⁺ stores by thapsigargin, addition of Ca²⁺ to the medium induced an increase in [Ca²⁺]i, indicating capacitative Ca²⁺ entry. Capacitative entry was found to be accelerated by low external Mg²⁺ and inhibited by high external Mg²⁺ concentration. Results suggest that receptor-mediated Ca²⁺ influx requires external Mg²⁺ but is inhibited by increased external Mg²⁺ concentrations and that capacitative Ca²⁺ entry is reduced by external Mg²⁺ in human coronary arterial ECs.

Key Words: extracellular magnesium • endothelial cells • calcium entry

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