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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 effect of 2-APB application during exposure to divalent cation- and Na+-free solutions. (0 Ca2+, 0 Mg2+, 0 Na+). Changes in [Mg2+]i and pHi are plotted in (A; ▪) and (B; •), respectively. After acquiring the control data in a Ca2+-free solution, extracellular Mg2+ and Na+ were simultaneously removed, and 150 μM 2-APB was added (n = 7). The spectra in Figures 1C and D correspond to this experiment. The data obtained in the absence of 2-APB (open symbols: □, ○; the same data shown in Fig. 2, n= 7)are also plotted to clearly show the inhibitory effect of 2-APB. Asterisks indicate statistically significant differences compared to the [Mg2+]i and pHi values before removal of extracellular Na+ (*, P<0.05;**, P<0.01). 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 (n= 7 in (–) and 150 μM 2-APB; n= 5 in 15 and 50 μM 2-APB).
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fig03: The effect of 2-APB application during exposure to divalent cation- and Na+-free solutions. (0 Ca2+, 0 Mg2+, 0 Na+). Changes in [Mg2+]i and pHi are plotted in (A; ▪) and (B; •), respectively. After acquiring the control data in a Ca2+-free solution, extracellular Mg2+ and Na+ were simultaneously removed, and 150 μM 2-APB was added (n = 7). The spectra in Figures 1C and D correspond to this experiment. The data obtained in the absence of 2-APB (open symbols: □, ○; the same data shown in Fig. 2, n= 7)are also plotted to clearly show the inhibitory effect of 2-APB. Asterisks indicate statistically significant differences compared to the [Mg2+]i and pHi values before removal of extracellular Na+ (*, P<0.05;**, P<0.01). 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 (n= 7 in (–) and 150 μM 2-APB; n= 5 in 15 and 50 μM 2-APB).

Mentions: 2-APB is known to block TRPM7 [11]. To substantiate the involvement of analogous Mg2+-permeable channels in vascular muscle cells, the effect of 2-APB was examined (Fig. 1C and D). As shown in Figure 3, application of 150 μM 2-APB to the divalent cation-and Na+-free solution significantly attenuated the depletion of [Mg2+]i (from 0.74 ± 0.05 to 0.62 ± 0.08 mM after 125 min; Fig. 3A, ▪). This inhibitory effect of 2-APB was concentration-dependent (Fig. 3C). The decrease in [Mg2+]i after 125 min was –0.27 ± 0.11 mM at 15 μM (n = 5), (0.22 ± 0.07 mM at 50 μM (n = 5) and –0.12±0.08 mM at 150 μM (n = 7). On the other hand, this drug had little effect on the changes in pHi (unpaired t-test, P >0.05, n = 7; Fig. 3B, •).


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 effect of 2-APB application during exposure to divalent cation- and Na+-free solutions. (0 Ca2+, 0 Mg2+, 0 Na+). Changes in [Mg2+]i and pHi are plotted in (A; ▪) and (B; •), respectively. After acquiring the control data in a Ca2+-free solution, extracellular Mg2+ and Na+ were simultaneously removed, and 150 μM 2-APB was added (n = 7). The spectra in Figures 1C and D correspond to this experiment. The data obtained in the absence of 2-APB (open symbols: □, ○; the same data shown in Fig. 2, n= 7)are also plotted to clearly show the inhibitory effect of 2-APB. Asterisks indicate statistically significant differences compared to the [Mg2+]i and pHi values before removal of extracellular Na+ (*, P<0.05;**, P<0.01). 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 (n= 7 in (–) and 150 μM 2-APB; n= 5 in 15 and 50 μM 2-APB).
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Related In: Results  -  Collection

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fig03: The effect of 2-APB application during exposure to divalent cation- and Na+-free solutions. (0 Ca2+, 0 Mg2+, 0 Na+). Changes in [Mg2+]i and pHi are plotted in (A; ▪) and (B; •), respectively. After acquiring the control data in a Ca2+-free solution, extracellular Mg2+ and Na+ were simultaneously removed, and 150 μM 2-APB was added (n = 7). The spectra in Figures 1C and D correspond to this experiment. The data obtained in the absence of 2-APB (open symbols: □, ○; the same data shown in Fig. 2, n= 7)are also plotted to clearly show the inhibitory effect of 2-APB. Asterisks indicate statistically significant differences compared to the [Mg2+]i and pHi values before removal of extracellular Na+ (*, P<0.05;**, P<0.01). 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 (n= 7 in (–) and 150 μM 2-APB; n= 5 in 15 and 50 μM 2-APB).
Mentions: 2-APB is known to block TRPM7 [11]. To substantiate the involvement of analogous Mg2+-permeable channels in vascular muscle cells, the effect of 2-APB was examined (Fig. 1C and D). As shown in Figure 3, application of 150 μM 2-APB to the divalent cation-and Na+-free solution significantly attenuated the depletion of [Mg2+]i (from 0.74 ± 0.05 to 0.62 ± 0.08 mM after 125 min; Fig. 3A, ▪). This inhibitory effect of 2-APB was concentration-dependent (Fig. 3C). The decrease in [Mg2+]i after 125 min was –0.27 ± 0.11 mM at 15 μM (n = 5), (0.22 ± 0.07 mM at 50 μM (n = 5) and –0.12±0.08 mM at 150 μM (n = 7). On the other hand, this drug had little effect on the changes in pHi (unpaired t-test, P >0.05, n = 7; Fig. 3B, •).

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