New vanadate-induced Ca2+ pathway in human red cells.
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 microM) in old cells. The results suggest presence of a new vanadate-induced Ca2+ entry pathway in ATP-depleted cells.
Romero
Pedro J
PJ
Laboratory of Membrane Physiology, Institute of Experimental Biology, Faculty of Sciences, Central University of Venezuela, Aptdo. 47114, Caracas 1041-A, Venezuela. romepe@mixmail.com
Romero
Eneida A
EA
D000255:Adenosine Triphosphate / Q000172:deficiency; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D016922:Cellular Senescence / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D045604:Extracellular Fluid / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D010085:Oxidative Phosphorylation / Q000187:drug effects; D018129:Phosphatidylinositol Phosphates / Q000037:antagonists & inhibitors / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology; D012964:Sodium / Q000172:deficiency; D014638:Vanadates / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D027682:Cation Transport Proteins; D007476:Ionophores; D018129:Phosphatidylinositol Phosphates; D012433:Ryanodine; D014638:Vanadates; D000255:Adenosine Triphosphate; D006493:Heparin; D012964:Sodium; D002118:Calcium