title: Up-regulation of megakaryocytic Na(+)/Ca(2+) exchange in klotho-deficient mice.
abstract: The active form of vitamin D, 1,25(OH)₂D₃, is a powerful regulator of cytosolic Ca(2+)-concentration ([Ca(2+)]i) in a variety of cell types. The formation of 1,25(OH)₂D₃ is inhibited by FGF23, an effect requiring presence of klotho. 1,25(OH)₂D₃ 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(2+) entry (SOCE). In other cell types 1,25(OH)₂D₃ has been shown to up-regulate the Na(+)/Ca(2+)-exchanger, which could, depending on cell membrane potential and cytosolic Na(+) concentration, either decrease or increase [Ca(2+)]i. The present study explored whether Na(+)/Ca(2+)-exchanger activity is different in megakaryocytes isolated from kl/kl mice than in megakaryocytes isolated from wild type mice. Na(+)/Ca(2+)-exchanger induced currents were determined by whole cell patch clamp and the Na(+)/Ca(2+)-exchanger induced alterations of [Ca(2+)]i by Fura-2 fluorescence. As a result, the inward current and the increase of [Ca(2+)]i following replacement of extracellular Na(+) 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)₂D₃ (100 nM, 48 h) was followed by enhancement of both, inward current and increase of [Ca(2+)]i following replacement of extracellular Na(+) by NMDG. In conclusion, the present observations reveal a powerful stimulating effect of 1,25(OH)₂D₃ on Na(+)/Ca(2+)-exchanger activity in megakaryocytes.
authors.affiliation: Department of Physiology, University of Tübingen, Gmelinstr. 5, 72076 Tuebingen, Germany; Department of Pediatric Surgery and Pediatric Urology, University Children's Hospital Tübingen, Hoppe-Seyler-Str. 3, 72076 Tübingen, Germany.
authors.forename: Evi
authors.initials: E
authors.lastname: Schmid
authors.affiliation: Department of Physiology, University of Tübingen, Gmelinstr. 5, 72076 Tuebingen, Germany.
authors.forename: Jing
authors.initials: J
authors.lastname: Yan
authors.affiliation: Department of Physiology, University of Tübingen, Gmelinstr. 5, 72076 Tuebingen, Germany.
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Hosseinzadeh
authors.affiliation: Department of Physiology, University of Tübingen, Gmelinstr. 5, 72076 Tuebingen, Germany.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Almilaji
authors.affiliation: Department of Physiology, University of Tübingen, Gmelinstr. 5, 72076 Tuebingen, Germany.
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Shumilina
authors.affiliation: Center for Molecular Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Kuro-o
authors.affiliation: Department of Cardiology and Cardiovascular Medicine, University of Tübingen, Otfried-Müller-Straße 10, 72076 Tübingen, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Borst
authors.affiliation: Department of Cardiology and Cardiovascular Medicine, University of Tübingen, Otfried-Müller-Straße 10, 72076 Tübingen, Germany.
authors.forename: Meinrad
authors.initials: M
authors.lastname: Gawaz
authors.affiliation: Department of Physiology, University of Tübingen, Gmelinstr. 5, 72076 Tuebingen, Germany. Electronic address: florian.lang@uni-tuebingen.de.
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005966:Glucuronidase / Q000235:genetics / Q000502:physiology*; D000090265:Klotho Proteins; D008297:Male; D008533:Megakaryocytes / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D018408:Patch-Clamp Techniques; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology*
chemical_list: C000717428:Fgf23 protein, mouse; D019831:Sodium-Calcium Exchanger; D000089703:Fibroblast Growth Factor-23; D005966:Glucuronidase; D000090265:Klotho Proteins; D002118:Calcium
keywords: Cytosolic Ca(2+); Megakaryocytes; Patch clamp; Platelets