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Mg2+ release coupled to Ca2+ uptake: A novel Ca2+ accumulation mechanism in rat liver

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Abstract

Isolated hepatocytes release 2–3 nmol Mg2+/mg protein or ~10% of the total cellular Mg2+ content within 2 minutes from the addition of agonists that increase cellular cAMP, for example, isoproterenol (ISO). During Mg2+ release, a quantitatively similar amount of Ca2+ enters the hepatocyte, thus suggesting a stoichiometric exchange ratio of 1 Mg2+:1Ca2+. Calcium induced Mg2+ extrusion is also observed in apical liver plasma membranes (aLPM), in which the process presents the same 1 Mg2+:1Ca2+ exchange ratio. The uptake of Ca2+ for the release of Mg2+ occurs in the absence of significant changes in Δψ as evidenced by electroneutral exchange measurements with a tetraphenylphosphonium (TPP+) electrode or 3H-TPP+. Collapsing the Δψ by high concentrations of TPP+ or protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) does not inhibit the Ca2+-induced Mg2+ extrusion in cells or aLPM. Further, the process is strictly unidirectional, serving only in Ca2+ uptake and Mg2+ release. These data demonstrate the operation of an electroneutral Ca2+/Mg2+ exchanger which represents a novel pathway for Ca2+ accumulation in liver cells following adrenergic receptor stimulation.

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Abbreviations

TPP+ :

tetraphenylphosphonium

SCN− :

sodium thiocyanate

aLPM:

apical liver plasma membranes

AAS:

atomic absorption spectrophotometry

FCCP:

protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone

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Acknowledgment

I thank Drs. Andrea Romani and Theresa Alexander for valuable discussion. This work was supported by National Institutes of Health Grant HL 18708.

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  1. Department Physiology and Biophysics, School of Medicine, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH, 44106-4970, USA

    C. Cefaratti

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  1. C. Cefaratti
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Correspondence to C. Cefaratti.

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This work was supported by National Institutes of Health Grant HL 18708.

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Cefaratti, C. Mg2+ release coupled to Ca2+ uptake: A novel Ca2+ accumulation mechanism in rat liver. Mol Cell Biochem 295, 241–247 (2007). https://doi.org/10.1007/s11010-006-9274-8

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