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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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Changes in the 31P-NMR spectrum during exposures to a divalent-cation-free, Na+-free solution. After acquiring the control spectrum in a Ca2+-free solution (a), extracel-lular Mg2+ and Na+ were simultaneously removed (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution) for 125 min. The spectra (b) and (c) were obtained during 25–50 min and 100–125 min periods, respectively. Each spectrum was obtained with 2500 signals accumulated over 25 min. The whole spectrum is shown in (A), and the β-ATP peaks are shown expanded in (B). The vertical line indicates the initial chemical shift of the β-ATP peak. The explanations are the same for the spectra in (C) and (D), but the divalent cation-free, Na+-free solution (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution) contained 150 μM 2-APB.
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fig01: Changes in the 31P-NMR spectrum during exposures to a divalent-cation-free, Na+-free solution. After acquiring the control spectrum in a Ca2+-free solution (a), extracel-lular Mg2+ and Na+ were simultaneously removed (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution) for 125 min. The spectra (b) and (c) were obtained during 25–50 min and 100–125 min periods, respectively. Each spectrum was obtained with 2500 signals accumulated over 25 min. The whole spectrum is shown in (A), and the β-ATP peaks are shown expanded in (B). The vertical line indicates the initial chemical shift of the β-ATP peak. The explanations are the same for the spectra in (C) and (D), but the divalent cation-free, Na+-free solution (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution) contained 150 μM 2-APB.

Mentions: Control spectra were acquired in the absence of Ca2+. Then, experiments were carried out in the absence of extracellular Na+ to rule out the contribution of Na+-coupled Mg2+ transport, that is, Na+–Mg2+ exchange. Six major peaks were observed (Fig. 1): phosphomonoesters (PME), inorganic phosphate (Pi), PCr and the γ-, α- and β-phosphorus atoms of ATP (γ-, α- and β-ATP).


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)

Changes in the 31P-NMR spectrum during exposures to a divalent-cation-free, Na+-free solution. After acquiring the control spectrum in a Ca2+-free solution (a), extracel-lular Mg2+ and Na+ were simultaneously removed (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution) for 125 min. The spectra (b) and (c) were obtained during 25–50 min and 100–125 min periods, respectively. Each spectrum was obtained with 2500 signals accumulated over 25 min. The whole spectrum is shown in (A), and the β-ATP peaks are shown expanded in (B). The vertical line indicates the initial chemical shift of the β-ATP peak. The explanations are the same for the spectra in (C) and (D), but the divalent cation-free, Na+-free solution (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution) contained 150 μM 2-APB.
© Copyright Policy
Related In: Results  -  Collection

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

fig01: Changes in the 31P-NMR spectrum during exposures to a divalent-cation-free, Na+-free solution. After acquiring the control spectrum in a Ca2+-free solution (a), extracel-lular Mg2+ and Na+ were simultaneously removed (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution) for 125 min. The spectra (b) and (c) were obtained during 25–50 min and 100–125 min periods, respectively. Each spectrum was obtained with 2500 signals accumulated over 25 min. The whole spectrum is shown in (A), and the β-ATP peaks are shown expanded in (B). The vertical line indicates the initial chemical shift of the β-ATP peak. The explanations are the same for the spectra in (C) and (D), but the divalent cation-free, Na+-free solution (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution) contained 150 μM 2-APB.
Mentions: Control spectra were acquired in the absence of Ca2+. Then, experiments were carried out in the absence of extracellular Na+ to rule out the contribution of Na+-coupled Mg2+ transport, that is, Na+–Mg2+ exchange. Six major peaks were observed (Fig. 1): phosphomonoesters (PME), inorganic phosphate (Pi), PCr and the γ-, α- and β-phosphorus atoms of ATP (γ-, α- and β-ATP).

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