New vanadate-induced Ca2+pathway in human red cells

Authors

  • Pedro J. Romero,

    Corresponding author
    1. Laboratory of Membrane Physiology, Institute of Experimental Biology, Faculty of Sciences, Central University of Venezuela, Aptdo. 47114, Caracas 1041-A, Venezuela
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  • Eneida A. Romero

    1. Laboratory of Membrane Physiology, Institute of Experimental Biology, Faculty of Sciences, Central University of Venezuela, Aptdo. 47114, Caracas 1041-A, Venezuela
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Corresponding author. Tel.: +58-212-7510766x222; fax: +58-212-753-7087 romepe@mixmail.com

Abstract

Vanadate is a commonly used Ca2+pump blocker, exerting a substantial effect on Ca2+extrusion at millimolar concentrations in human red cells. At such levels, vanadate also seems to open an L type-like Ca2+channel in these cells (J Biol Chem 257 (1982) 7414; Gen Physiol Biophys 16 (1997) 359). Since neither a dose-dependence effect nor a metabolic requirement for the latter action could be found in the literature, we have addressed this matter in the present work. Accordingly, vanadate action on Ca2+entry was systematically investigated in both young and old human red cells after metabolic depletion. Although vanadate enhanced Ca2+entry indifferently in either cell type, a distinct over-all effect was paradoxically found depending on whether or not metabolic substrates that give rise to ATP were present. In ATP-depleted cells, unlike with ATP-containing cells, vanadate-stimulated Ca2+entry was neither blocked by raising external K+nor by adding voltage-dependent Ca2+channel blockers (nifedipine, calciseptine, FTX3.3) or compounds affecting polyphosphoinositide metabolism (Li+, neomycin). Likewise, full substitution of external Na+by other cations did not inhibit vanadate-enhanced Ca2+entry. Regardless of the cell age, stimulation by vanadate depended strongly on internal Na+(0–30 mM). Vanadate stimulation was significantly reduced (about 55%) by heparin (10 mg/ml) only in young cells and by ryanodine (about 35%, 250 μM) in old cells. The results suggest presence of a new vanadate-induced Ca2+entry pathway in ATP-depleted cells.

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