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Na(+)-independent Mg(2+) transport sensitive to 2-aminoethoxydiphenyl borate (2-APB) in vascular smooth muscle cells: involvement of TRPM-like channels.

Hamaguchi Y, Matsubara T, Amano T, Uetani T, Asano H, Iwamoto T, Furukawa K, Murohara T, Nakayama S - J. Cell. Mol. Med. (2008)

Bottom Line: RT-PCR detected transcripts of both TRPM6 and TRPM7, although TRPM7 was predominant.In conclusion, the results suggest the presence of Mg(2+)-permeable channels of TRPM family that contribute to Mg(2+) homeostasis in vascular smooth muscle cells.The low, basal [Mg(2+)](i) level in vascular smooth muscle cells is attributable to the relatively low activity of this Mg(2+) entry pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Cardiology, Nagoya University Graduate School of Medicine, Nagoya, Japan.

ABSTRACT
Magnesium is associated with several important cardiovascular diseases. There is an accumulating body of evidence verifying the important roles of Mg(2+)-permeable channels. In the present study, we estimated the intracellular free Mg(2+) concentration ([Mg(2+)](i)) using (31)P-nuclear magnetic resonance ((31)P-NMR) in porcine carotid arteries. pH(i) and intracellular phosphorus compounds were simultaneously monitored. Removal of extracellular divalent cations (Ca(2+) and Mg(2+)) in the absence of Na(+) caused a gradual decrease in [Mg(2+)](i) to approximately 60% of the control value after 125 min. On the other hand, the simultaneous removal of extracellular Ca(2+) and Na(+) in the presence of Mg(2+) gradually increased [Mg(2+)](i) in an extracellular Mg(2+)-dependent manner. 2-aminoethoxydiphenyl borate (2-APB) attenuated both [Mg(2+)](i) load and depletion caused under Na(+)- and Ca(2+)-free conditions. Neither [ATP](i) nor pH(i) correlated with changes in [Mg(2+)](i). RT-PCR detected transcripts of both TRPM6 and TRPM7, although TRPM7 was predominant. In conclusion, the results suggest the presence of Mg(2+)-permeable channels of TRPM family that contribute to Mg(2+) homeostasis in vascular smooth muscle cells. The low, basal [Mg(2+)](i) level in vascular smooth muscle cells is attributable to the relatively low activity of this Mg(2+) entry pathway.

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The inhibitory effect of 2-APB on [Mg2+]i rise in Mg2+-containing solutions. In (A), after acquiring the control data in a Ca2+-free solution, the extracellular Mg2+ was increased to 6.0 mM, Na+ was removed, and 150 μM 2-APB was added in the extracellular solution. The data indicated by open symbols (□) represent experiments without 2-APB (the same data shown in Fig. 4A, □). In (B), extracellular Na+ was substituted with NMDG. Crosses on filled symbols (□, ○) indicate statistically significant differences compared to the open symbols at the same time point (†, P<0.05;††, P<0.01). Bar graphs in (C) indicate effects of 15, 50 and 150 μM 2-APB during 125–150 min in the presence of Ca2+ (n= 4 for each experiment).
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fig05: The inhibitory effect of 2-APB on [Mg2+]i rise in Mg2+-containing solutions. In (A), after acquiring the control data in a Ca2+-free solution, the extracellular Mg2+ was increased to 6.0 mM, Na+ was removed, and 150 μM 2-APB was added in the extracellular solution. The data indicated by open symbols (□) represent experiments without 2-APB (the same data shown in Fig. 4A, □). In (B), extracellular Na+ was substituted with NMDG. Crosses on filled symbols (□, ○) indicate statistically significant differences compared to the open symbols at the same time point (†, P<0.05;††, P<0.01). Bar graphs in (C) indicate effects of 15, 50 and 150 μM 2-APB during 125–150 min in the presence of Ca2+ (n= 4 for each experiment).

Mentions: To assess whether the same Mg2+-permeable channels contributed to the inward and outward transport of Mg2+ under Na+-free conditions, we examined the effect of 2-APB in the presence of Mg2+. 2-APB (150 μM) was applied to a Ca2+- and Na+-free solution containing 6.0 mM Mg2+ (Supplementary Fig. S1, B). After 125 min, [Mg2+]i increased from 0.75±0.04 to 1.14±0.08 mM (Fig. 5A, ▪; n = 7; P<0.01), but this increase in [Mg2+]i was significantly smaller than without 2-APB (unpaired t-test, P<0.01). On the other hand, pHi with and without 2-APB, was comparable throughout experiments (not shown).


Na(+)-independent Mg(2+) transport sensitive to 2-aminoethoxydiphenyl borate (2-APB) in vascular smooth muscle cells: involvement of TRPM-like channels.

Hamaguchi Y, Matsubara T, Amano T, Uetani T, Asano H, Iwamoto T, Furukawa K, Murohara T, Nakayama S - J. Cell. Mol. Med. (2008)

The inhibitory effect of 2-APB on [Mg2+]i rise in Mg2+-containing solutions. In (A), after acquiring the control data in a Ca2+-free solution, the extracellular Mg2+ was increased to 6.0 mM, Na+ was removed, and 150 μM 2-APB was added in the extracellular solution. The data indicated by open symbols (□) represent experiments without 2-APB (the same data shown in Fig. 4A, □). In (B), extracellular Na+ was substituted with NMDG. Crosses on filled symbols (□, ○) indicate statistically significant differences compared to the open symbols at the same time point (†, P<0.05;††, P<0.01). Bar graphs in (C) indicate effects of 15, 50 and 150 μM 2-APB during 125–150 min in the presence of Ca2+ (n= 4 for each experiment).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4401140&req=5

fig05: The inhibitory effect of 2-APB on [Mg2+]i rise in Mg2+-containing solutions. In (A), after acquiring the control data in a Ca2+-free solution, the extracellular Mg2+ was increased to 6.0 mM, Na+ was removed, and 150 μM 2-APB was added in the extracellular solution. The data indicated by open symbols (□) represent experiments without 2-APB (the same data shown in Fig. 4A, □). In (B), extracellular Na+ was substituted with NMDG. Crosses on filled symbols (□, ○) indicate statistically significant differences compared to the open symbols at the same time point (†, P<0.05;††, P<0.01). Bar graphs in (C) indicate effects of 15, 50 and 150 μM 2-APB during 125–150 min in the presence of Ca2+ (n= 4 for each experiment).
Mentions: To assess whether the same Mg2+-permeable channels contributed to the inward and outward transport of Mg2+ under Na+-free conditions, we examined the effect of 2-APB in the presence of Mg2+. 2-APB (150 μM) was applied to a Ca2+- and Na+-free solution containing 6.0 mM Mg2+ (Supplementary Fig. S1, B). After 125 min, [Mg2+]i increased from 0.75±0.04 to 1.14±0.08 mM (Fig. 5A, ▪; n = 7; P<0.01), but this increase in [Mg2+]i was significantly smaller than without 2-APB (unpaired t-test, P<0.01). On the other hand, pHi with and without 2-APB, was comparable throughout experiments (not shown).

Bottom Line: RT-PCR detected transcripts of both TRPM6 and TRPM7, although TRPM7 was predominant.In conclusion, the results suggest the presence of Mg(2+)-permeable channels of TRPM family that contribute to Mg(2+) homeostasis in vascular smooth muscle cells.The low, basal [Mg(2+)](i) level in vascular smooth muscle cells is attributable to the relatively low activity of this Mg(2+) entry pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Cardiology, Nagoya University Graduate School of Medicine, Nagoya, Japan.

ABSTRACT
Magnesium is associated with several important cardiovascular diseases. There is an accumulating body of evidence verifying the important roles of Mg(2+)-permeable channels. In the present study, we estimated the intracellular free Mg(2+) concentration ([Mg(2+)](i)) using (31)P-nuclear magnetic resonance ((31)P-NMR) in porcine carotid arteries. pH(i) and intracellular phosphorus compounds were simultaneously monitored. Removal of extracellular divalent cations (Ca(2+) and Mg(2+)) in the absence of Na(+) caused a gradual decrease in [Mg(2+)](i) to approximately 60% of the control value after 125 min. On the other hand, the simultaneous removal of extracellular Ca(2+) and Na(+) in the presence of Mg(2+) gradually increased [Mg(2+)](i) in an extracellular Mg(2+)-dependent manner. 2-aminoethoxydiphenyl borate (2-APB) attenuated both [Mg(2+)](i) load and depletion caused under Na(+)- and Ca(2+)-free conditions. Neither [ATP](i) nor pH(i) correlated with changes in [Mg(2+)](i). RT-PCR detected transcripts of both TRPM6 and TRPM7, although TRPM7 was predominant. In conclusion, the results suggest the presence of Mg(2+)-permeable channels of TRPM family that contribute to Mg(2+) homeostasis in vascular smooth muscle cells. The low, basal [Mg(2+)](i) level in vascular smooth muscle cells is attributable to the relatively low activity of this Mg(2+) entry pathway.

Show MeSH
Related in: MedlinePlus