Ca2+ mobilization induced by ouabain in thymocytes involves intracellular and extracellular Ca2+ pools. 2003

Juliana Echevarria-Lima, and Elizabeth Giestal de Araújo, and Leopoldo de Meis, and Vivian M Rumjanek
Laboratório de Imunologia Tumoral, Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Brazil.

Immune dysfunction has been reported in hypertensive rats, and circulating levels of ouabain are increased in some experimental models of hypertension. Ouabain is an inhibitor of the Na+/K+-ATPase capable of diverse effects on cells of the immune system, but its mode of action on these cells is still unknown. The levels of cytoplasmic calcium ions play an important role in cell signaling, and ouabain may induce an increase in intracellular calcium indirectly through the Na+/Ca2+ exchanger. The current work examined the possibility that this drug could be exerting its effects on thymocytes through calcium mobilization and an increase in the cytosolic calcium concentration. Intracellular calcium was evaluated by using Balb-c mouse thymocytes loaded with FURA-2. Both intracellular and extracellular calcium pools were mobilized by ouabain (3 to 1000 nmol). The influx of extracellular calcium depended on the Na+/Ca2+ exchanger and on voltage-dependent calcium channels, as it was inhibited by amiloride and benzamil, consistent with the inhibition of the Na+/K+ pump. In addition, the increase of calcium from intracellular stores was extremely rapid. Furthermore, an increase in cytosolic calcium levels was obtained with the combination of ouabain and thapsigargin, which was greater than that seen with either drug alone. Our data suggest that low concentrations of ouabain may be acting on thymocytes through a mechanism different from the traditional inhibition of the Na+/K+-ATPase, as the cytosolic calcium rise was partly dependent on the release from intracellular stores.

UI MeSH Term Description Entries
D008297 Male Males
D008564 Membrane Potentials The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization). Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D008807 Mice, Inbred BALB C An inbred strain of mouse that is widely used in IMMUNOLOGY studies and cancer research. BALB C Mice, Inbred,BALB C Mouse, Inbred,Inbred BALB C Mice,Inbred BALB C Mouse,Mice, BALB C,Mouse, BALB C,Mouse, Inbred BALB C,BALB C Mice,BALB C Mouse
D010042 Ouabain A cardioactive glycoside consisting of rhamnose and ouabagenin, obtained from the seeds of Strophanthus gratus and other plants of the Apocynaceae; used like DIGITALIS. It is commonly used in cell biological studies as an inhibitor of the NA(+)-K(+)-EXCHANGING ATPASE. Acocantherin,G-Strophanthin,Acolongifloroside K,G Strophanthin
D002118 Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D002462 Cell Membrane The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells. Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D002478 Cells, Cultured Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others. Cultured Cells,Cell, Cultured,Cultured Cell
D003600 Cytosol Intracellular fluid from the cytoplasm after removal of ORGANELLES and other insoluble cytoplasmic components. Cytosols
D004357 Drug Synergism The action of a drug in promoting or enhancing the effectiveness of another drug. Drug Potentiation,Drug Augmentation,Augmentation, Drug,Augmentations, Drug,Drug Augmentations,Drug Potentiations,Drug Synergisms,Potentiation, Drug,Potentiations, Drug,Synergism, Drug,Synergisms, Drug
D004791 Enzyme Inhibitors Compounds or agents that combine with an enzyme in such a manner as to prevent the normal substrate-enzyme combination and the catalytic reaction. Enzyme Inhibitor,Inhibitor, Enzyme,Inhibitors, Enzyme

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