Author(s) : Kazuo Satake, Jong‐Dae Lee, Hiromasa Shimizu, Hiroyasu Uzui, Yasuhiko Mitsuke, Hong Yue, Takanori Ueda , First Department of Internal Medicine, Fukui University, 23 Shimoaizuki, Matsuoka‐cho, Fukui 910‐1193, Japan .
Summary : This study investigated the effects of extracellular magnesium concentration ([Mg
2+]e\; 0.3‐3 mM) on intracellular free calcium concentration ([Ca
2+]i) and prostacyclin (PGI
2) production in cultured human umbilical vein endothelial cells (HUVEC) and vascular smooth muscle cells from rats (VSMC) under basal and agonist‐stimulated conditions. We used histamine as agonist which increases [Ca
2+]i and PGI
2 production in HUVEC, norepinephrine in VSMC. [Mg
2+]e dose‐dependently increased basal and agonist‐stimulated PGI
2 production in both cells. [Mg
2+]e dose‐dependently reduced basal [Ca
2+]i in VSMC, but did not influence in HUVEC. In both cells, increasing [Mg
2+]e reduced agonist‐stimulated [Ca
2+]i responses. Furthermore, [Mg
2+]e dose‐dependently reduced agonist‐stimulated [Ca
2+]i in Ca
2+ ‐free buffer, indicating intracellular Ca
2+ release. In VSMC, 10
‐‐6 M diltiazem and 10
‐7 M nifedipine, Ca
2+ channel blockers, reduced agonist‐stimulated [Ca
2+]i as well as 3 mM Mg
2+, but did not affect PGI
2 production. [Mg
2+]e amplified dose‐dependently arachidonic acid‐induced PGI
2 production in both cells, suggesting the activation of cyclooxygenase and\\or PGI
2 synthetase. Our results suggest that [Mg
2+]e influences intracellular Ca
2+ mobilization of not only vascular smooth muscle cells but also endothelial cells by inhibiting both Ca
2+ influx and intracellular Ca
2+ release. [Mg
2+]e enhances PGI
2 production in both types of cells, although the mechanism is likely to be independent from Ca
2+ mobilization.
Fig. 1. Effects of extracellular
Mg2+ on basal and agonist-stimulated PGI2
production by HUVEC. Cultured HUVEC were incubated in Hepes buffer
A (see Methods) containing 0.3-3 mM Mg2+ in the
presence (close circle) or absence (open circle) of 10–5
M histamine. The supernatant was assayed by RIA. Data are
represented as means ± SEM (n = 6). *
P < 0.05 compared with 0.3 mM
Mg2+
Fig. 2. Effects of extracellular
Mg2+ on basal [Ca2+]i and
10–5 M histamine-stimulated
[Ca2+]i transients in HUVEC. Cultured HUVEC
were loaded with 2 µM fura2-AM and resuspended in Hepes buffer
B (see Methods) containing 0.3-3 mM MgSO4 with
(Panel A) or without (Panel B) 2.5 mM CaCl2 Data
were obtained in the presence (close circle) or absence (open
circle) of 10–5 M histamine. Data are represented as
means ± SEM (n = 8). *
P < 0.05 compared with 0.3 mM
Mg2+.
Fig. 3. Effects of extracellular
Mg2+ on PGI2 production by VSMC. Cultured
VSMC were incubated in Hepes buffer A (see Methods) containing
0.3-3 mM Mg2+ in the presence (close circle) or
absence (open circle) of 10–6 M norepinephrine. The
supernatant was assayed by RIA. Data are represented as
means ± SEM (n = 8). *
P < 0.05 compared with 0.3 mM
Mg2+.
Fig. 4. Effects of Ca2+
channel blockers on 10–6 M norepinephrine-stimulated
[Ca2+]i transients and PGI2 production in
VSMC. Panel (A) demonstrates 10–6 M
norepinephrine-stimulated [Ca2+]i transients
in Hepes buffer B (see Methods). Panel (B) shows 10–6 M
norepinephrine-stimulated PGI2 production in Hepes
buffer A (see Methods). Data are represented as
means ± SEM (n = 8). * Significantly different
at P < 0.05. NS indicates no statistically significant
difference.
Fig. 5. Effects of extracellular
Mg2+ on sodium arachidonate-stimulated PGI2
production by HUVEC and VSMC. HUVEC and VSMC were incubated in
Hepes buffer A (see methods) containing 0.3-3 mM
Mg2+ with 20 µM arachidonic acid (Panel (A): HUVEC,
Panel (B): VSMC). The supernatant was assayed by RIA. Data are
represented as means ± SEM (n = 8). *
Significantly differs (P < 0.05) from corresponding
values obtained with 0.3 mM Mg2+ *
P < 0.05 compared with 0.3 mM
Mg2+.
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