Up-regulation of megakaryocytic Na<sup>+</sup>/Ca<sup>2+</sup> exchange in klotho-deficient mice

Evi Schmid, Jing Yan, Zohreh Hosseinzadeh, Ahmad Almilaji, Ekaterina Shumilina, Makoto Kuro-O, Oliver Borst, Meinrad Gawaz, Florian Lang

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Abstract

The active form of vitamin D, 1,25(OH)<inf>2</inf>D<inf>3</inf>, is a powerful regulator of cytosolic Ca<sup>2+</sup>-concentration ([Ca<sup>2+</sup>]<inf>i</inf>) in a variety of cell types. The formation of 1,25(OH)<inf>2</inf>D<inf>3</inf> is inhibited by FGF23, an effect requiring presence of klotho. 1,25(OH)<inf>2</inf>D<inf>3</inf> plasma levels are excessive in klotho-deficient mice (kl/kl). A previous study revealed that klotho-deficiency is followed by decreased activation of platelets, an effect at least in part due to blunted store operated Ca<sup>2+</sup> entry (SOCE). In other cell types 1,25(OH)<inf>2</inf>D<inf>3</inf> has been shown to up-regulate the Na<sup>+</sup>/Ca<sup>2+</sup>-exchanger, which could, depending on cell membrane potential and cytosolic Na<sup>+</sup> concentration, either decrease or increase [Ca<sup>2+</sup>]<inf>i</inf>. The present study explored whether Na<sup>+</sup>/Ca<sup>2+</sup>-exchanger activity is different in megakaryocytes isolated from kl/kl mice than in megakaryocytes isolated from wild type mice. Na<sup>+</sup>/Ca<sup>2+</sup>-exchanger induced currents were determined by whole cell patch clamp and the Na<sup>+</sup>/Ca<sup>2+</sup>-exchanger induced alterations of [Ca<sup>2+</sup>]<inf>i</inf> by Fura-2 fluorescence. As a result, the inward current and the increase of [Ca<sup>2+</sup>]<inf>i</inf> following replacement of extracellular Na<sup>+</sup> by NMDG were higher in kl/kl megakaryocytes than in wild type megakaryocytes, a difference abrogated by treatment of the mice with low Vitamin D diet. Pretreatment of wild type megakaryocytes with 1,25(OH)<inf>2</inf>D<inf>3</inf> (100 nM, 48 h) was followed by enhancement of both, inward current and increase of [Ca<sup>2+</sup>]<inf>i</inf> following replacement of extracellular Na<sup>+</sup> by NMDG. In conclusion, the present observations reveal a powerful stimulating effect of 1,25(OH)<inf>2</inf>D<inf>3</inf> on Na<sup>+</sup>/Ca<sup>2+</sup>-exchanger activity in megakaryocytes.

Original languageEnglish (US)
Pages (from-to)177-182
Number of pages6
JournalBiochemical and Biophysical Research Communications
Volume460
Issue number2
DOIs
Publication statusPublished - May 1 2015

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Keywords

  • Cytosolic Ca<sup>2+</sup>
  • Megakaryocytes
  • Patch clamp
  • Platelets

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Cell Biology
  • Molecular Biology
  • Medicine(all)

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