J Vet Sci.  2006 Mar;7(1):31-36. 10.4142/jvs.2006.7.1.31.

pH-dependent modulation of intracellular free magnesium ions with ionselective electrodes in papillary muscle of guinea pig

• Kim SJ
• Cho IG
• Kang HS
• Kim JS

• KMID: 1103550
• DOI: http://doi.org/10.4142/jvs.2006.7.1.31

Abstract

A change in pH can alter the intracellular concentration of electrolytes such as intracellular Ca2+ and Na+ ([Na+]i) that are important for the cardiac function. For the determination of the role of pH in the cardiac magnesium homeostasis, the intracellular Mg2+ concentration ([Mg2+]i), membrane potential and contraction in the papillary muscle of guinea pigs using ion-selective electrodes changing extracellular pH ([pH]o) or intracellular pH ([pH]i) were measured in this study. A high CO2-induced low [pH]o causes a significant increase in the [Mg2+]i and [Na+]i, which was accompanied by a decrease in the membrane potential and twitch force. The high [pH]o had the opposite effect. These effects were reversible in both the beating and quiescent muscles. The low [pH]o-induced increase in [Mg2+]i occurred in the absence of [Mg2+]o. The [Mg2+]i was increased by the low [pH]i induced by propionate. The [Mg2+]i was increased by the low [pH]i induced by NH4Cl-prepulse and decreased by the recovery of [pH]i induced by the removal of NH4Cl. These results suggest that the pH can modulate [Mg2+]i with a reverse relationship in heart, probably by affecting the intracellular Mg2+ homeostasis, but not by Mg2+ transport across the sarcolemma.

Keyword

ion-selective electrodes; guinea pig; magnesium; papillary muscle

MeSH Terms

Animals
Cations, Divalent
Female
Guinea Pigs
Heart Ventricles/metabolism
Hydrogen-Ion Concentration
Ion Transport/physiology
Ion-Selective Electrodes/veterinary
Magnesium/*metabolism
Male
Membrane Potentials/physiology
Papillary Muscles/*metabolism
Propionates/pharmacology
Sodium/*metabolism

Figure

• 

  Fig. 1 Effects of changes in [pH]o on [Mg2+]i in papillary muscle. Typical recordings of the membrane potential (Em), intracellular Mg2+ concentration ([Mg2+]i) and twitch force (TF) during the change in extracellular pH ([pH]o) in the beating state. Extracellular acidification was induced by regulating the CO2/O2 composition.

• 

  Fig. 2 Effects of low [pH]o on the [Na+]i. Typical recordings of the Em, [Na+]i and TF during a change in [pH]o in the beating state. Extracellular acidification was induced by regulating the CO2/O2 composition.

• 

  Fig. 3 Effects of [Mg2+]o on low [pH]o-induced increase in [Mg2+]i. Typical recordings of the Em and [Mg2+]i during a change in [pH]o in the absence and presence of [Mg2+]o in a quiescent muscle. Extracellular acidification was induced by regulating the CO2/O2 composition. No MgCl2 was added to the Mg2+-free solution (nominally absence of extracellular Mg2+).

• 

  Fig. 4 Effects of propionate on the [Mg2+]i. Typical recordings of the Em, [Mg2+]i and TF during the application of 20 mM Na+-propionate. All experiments were at constant [pH]o of 7.4. The NaCl in the Tyrode solution was replaced Na+-propionate.

• 

  Fig. 5 Effects of NH4Cl on [Mg2+]i. Typical recordings of the Em, [Mg2+]i and TF during the application of 10 mM NH4Cl. All the experiments were at constant [pH]o of 7.4. For the control, the choline chloride was added to the Thyroid solution.

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