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Effects of pH and anion substitution on magnesium accumulation in rabbit aortic smooth muscle
1Research Department, Ciba-Geigy Corporation, Summit, N.J.
Abstract:
The effects of anion substitution, pH and extracellular Mg2+ concentration on 28Mg accumulation were examined in rabbit aortic smooth muscle. Accumulation of 28Mg (expressed as a 28Mg/Mg2+ ratio) was not changed when the concentration of added, nonradioactive MgCl2 was increased from 1.5 to 15.0 mM. The 28Mg efflux rate was increased by added MgCl2 (0.15, 0.5 or 1.5 mM) in a dose-related manner after a similar delay of 5-10 min. Addition of 1.5 mM MgCl2, MgSO4 or magnesium aspartate hydrochloride enhanced 28Mg efflux and inhibited accumulation of 28Mg to the same extent. An increase or decrease in extracellular pH correspondingly increased or decreased 28Mg accumulation. However, the 28Mg efflux rate was not altered when extracellular pH was decreased. Efflux of 28Mg was increased by added 1.5 mM MgCl2 at pH 7.4 but not at pH 5.8. Thus, the net uptake of Mg2+ appears to be proportional to the concentration of extracellular Mg2+ in rabbit aorta. Low external pH decreases 28Mg retention in rabbit aorta by inhibiting the uptake of 28Mg rather than by increasing 28Mg efflux. Effects of added Mg2+ on transmembrane movements of 28Mg are not altered by changes in the associated anion. Extracellular Mg2+ appears to enter the cell and exchange with an intracellularly located pool of 28Mg in the same manner, regardless of whether the accompanying anion is sulfate, chloride or monoaspartate hydrochloride.
Insights
Magnesium (Mg2+) uptake in rabbit aorta is proportional to extracellular Mg2+ concentration. Low external pH reduces Mg2+ retention by inhibiting uptake, not increasing efflux.
Area of Science:
- Physiology
- Biochemistry
- Cell Biology
Background:
- Magnesium is crucial for cellular function.
- Understanding magnesium transport is vital for cardiovascular health.
Purpose of the Study:
- To investigate factors influencing magnesium (Mg2+) accumulation in rabbit aortic smooth muscle.
- To determine the impact of anion type, pH, and extracellular Mg2+ concentration on Mg2+ transmembrane movements.
Main Methods:
- Utilized 28Mg as a radioactive tracer to quantify Mg2+ accumulation and efflux.
- Manipulated extracellular Mg2+ concentration, pH, and anion composition (MgCl2, MgSO4, magnesium aspartate hydrochloride).
Main Results:
- Mg2+ accumulation was directly proportional to extracellular Mg2+ concentration.
- Increased extracellular Mg2+ enhanced Mg2+ efflux in a dose-dependent manner.
- Low extracellular pH (acidosis) inhibited Mg2+ uptake but did not significantly affect efflux.
- Anion substitution did not alter the effects of Mg2+ on transmembrane movements.
Conclusions:
- Extracellular Mg2+ concentration is a primary determinant of Mg2+ uptake in rabbit aorta.
- Low pH impairs Mg2+ retention by reducing cellular influx.
- Magnesium transport mechanisms are largely independent of the accompanying anion.