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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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Time course of changes in [Mg2+]i (A: squares) and pHi (B: circles) during exposure to divalent cation-free solutions. After control measurements in a Ca2+-free solution (control), extracellular Mg2+ was also removed for 125 min. Each point was obtained from the accumulation of NMR signals over 25 min. The open (□, ○) and filled symbols (▪, •) represent the data obtained under exposures to Na+-free (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution; n = 7) and Na+-containing solutions (0 Ca2+, 0 Mg2+; n = 7), respectively. The spectra shown in Fig. 1A and B correspond to this Na+-free experiment. The dotted lines indicate the mean value of [Mg2+]i and pHi before exposure to the divalent cation-free solutions (n= 14 for all preparations shown in this figure). Vertical bars represent S.D. values. Asterisks indicate statistically significant differences compared to the [Mg2+]i and pHi values before removal of extracellu-lar Mg2+ (*, P<0.05; **, P<0.01). Crosses on filled symbols, in the presence of Na+, indicate statistically significant differences compared to the open symbols, in the absence of Na+, at the same time point (†, P<0.05; ††, P<0.01).
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fig02: Time course of changes in [Mg2+]i (A: squares) and pHi (B: circles) during exposure to divalent cation-free solutions. After control measurements in a Ca2+-free solution (control), extracellular Mg2+ was also removed for 125 min. Each point was obtained from the accumulation of NMR signals over 25 min. The open (□, ○) and filled symbols (▪, •) represent the data obtained under exposures to Na+-free (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution; n = 7) and Na+-containing solutions (0 Ca2+, 0 Mg2+; n = 7), respectively. The spectra shown in Fig. 1A and B correspond to this Na+-free experiment. The dotted lines indicate the mean value of [Mg2+]i and pHi before exposure to the divalent cation-free solutions (n= 14 for all preparations shown in this figure). Vertical bars represent S.D. values. Asterisks indicate statistically significant differences compared to the [Mg2+]i and pHi values before removal of extracellu-lar Mg2+ (*, P<0.05; **, P<0.01). Crosses on filled symbols, in the presence of Na+, indicate statistically significant differences compared to the open symbols, in the absence of Na+, at the same time point (†, P<0.05; ††, P<0.01).

Mentions: During exposure to a divalent cation-free solution (i.e. 0 Ca2+, 0 Mg2+), [Mg2+]i decreased from from 0.74±0.11 to 0.49±0.08 mM (n = 7; Fig. 2A, ▪) after 125 min, while pHi did not change significantly (Fig. 2B, •). Essentially the same decrease in [Mg2+]i (from 0.75±0.09 to 0.46±0.05 mM; n = 7; Fig. 2A, □) was observed in the absence of Na+, suggesting that Mg2+-permeable channels make a major contribution to the changes in [Mg2+]i under divalent cation-free conditions. On the other hand, pHi decreased from 7.09 ±0.05 to 6.92 ±0.05 (n = 7) after 125 min in the absence of Na+ (Fig. 2B, ○), presumably due to the inhibition of Na+-coupled pHi regulatory mechanisms, such as Na+-H+ exchange and Na+-HCO3− co-transport.


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)

Time course of changes in [Mg2+]i (A: squares) and pHi (B: circles) during exposure to divalent cation-free solutions. After control measurements in a Ca2+-free solution (control), extracellular Mg2+ was also removed for 125 min. Each point was obtained from the accumulation of NMR signals over 25 min. The open (□, ○) and filled symbols (▪, •) represent the data obtained under exposures to Na+-free (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution; n = 7) and Na+-containing solutions (0 Ca2+, 0 Mg2+; n = 7), respectively. The spectra shown in Fig. 1A and B correspond to this Na+-free experiment. The dotted lines indicate the mean value of [Mg2+]i and pHi before exposure to the divalent cation-free solutions (n= 14 for all preparations shown in this figure). Vertical bars represent S.D. values. Asterisks indicate statistically significant differences compared to the [Mg2+]i and pHi values before removal of extracellu-lar Mg2+ (*, P<0.05; **, P<0.01). Crosses on filled symbols, in the presence of Na+, indicate statistically significant differences compared to the open symbols, in the absence of Na+, at the same time point (†, P<0.05; ††, P<0.01).
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fig02: Time course of changes in [Mg2+]i (A: squares) and pHi (B: circles) during exposure to divalent cation-free solutions. After control measurements in a Ca2+-free solution (control), extracellular Mg2+ was also removed for 125 min. Each point was obtained from the accumulation of NMR signals over 25 min. The open (□, ○) and filled symbols (▪, •) represent the data obtained under exposures to Na+-free (0 Ca2+, 0 Mg2+, 0 Na+: K+ substitution; n = 7) and Na+-containing solutions (0 Ca2+, 0 Mg2+; n = 7), respectively. The spectra shown in Fig. 1A and B correspond to this Na+-free experiment. The dotted lines indicate the mean value of [Mg2+]i and pHi before exposure to the divalent cation-free solutions (n= 14 for all preparations shown in this figure). Vertical bars represent S.D. values. Asterisks indicate statistically significant differences compared to the [Mg2+]i and pHi values before removal of extracellu-lar Mg2+ (*, P<0.05; **, P<0.01). Crosses on filled symbols, in the presence of Na+, indicate statistically significant differences compared to the open symbols, in the absence of Na+, at the same time point (†, P<0.05; ††, P<0.01).
Mentions: During exposure to a divalent cation-free solution (i.e. 0 Ca2+, 0 Mg2+), [Mg2+]i decreased from from 0.74±0.11 to 0.49±0.08 mM (n = 7; Fig. 2A, ▪) after 125 min, while pHi did not change significantly (Fig. 2B, •). Essentially the same decrease in [Mg2+]i (from 0.75±0.09 to 0.46±0.05 mM; n = 7; Fig. 2A, □) was observed in the absence of Na+, suggesting that Mg2+-permeable channels make a major contribution to the changes in [Mg2+]i under divalent cation-free conditions. On the other hand, pHi decreased from 7.09 ±0.05 to 6.92 ±0.05 (n = 7) after 125 min in the absence of Na+ (Fig. 2B, ○), presumably due to the inhibition of Na+-coupled pHi regulatory mechanisms, such as Na+-H+ exchange and Na+-HCO3− co-transport.

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