Calcium fluxes in T lymphocytes.
Mechanisms controlling Ca2+ fluxes through the plasma membrane of lymphocytes have been characterized in a human T-cell clone and in the Jurkat T-cell line. Due to endogenous buffers, about 1/125 of the Ca2+ ions that enter the cell are free. Ca2+ fluxes were estimated from the variations in intracellular Ca2+ concentration ([Ca2+]i) elicited by concentration jumps in extracellular Ca2+ ([Ca2+]o). Thapsigargin was used to inhibit Ca2+ uptake into intracellular stores and to stimulate Ca2+ entry. Ca2+ extrusion was strictly due to the activity of plasma membrane Ca(2+)-ATPases since there was no detectable Na+/Ca2+ exchange activity in these cells. The rate of Ca2+ extrusion was mainly influenced by [Ca2+]i and less by [Ca2+]o but was insensitive to cell depolarization. In depolarized cells, thapsigargin-induced Ca2+ influx was reduced to 10% of the value measured in normally polarized cells, suggesting that depolarization not only reduces the electrochemical gradient for Ca2+ ions, but also inhibits Ca2+ permeation. When Ca2+ ions enter the cell, they bind to a site inside the channel, with a Kd of 3.3 mM. Stimulation of clonal T-cells with low concentrations of either anti-CD3 antibodies or thapsigargin elicited Ca2+ oscillations. Both the amplitude and the frequency of CD3-induced Ca2+ oscillations were sensitive to [Ca2+]o. These oscillations were immediately interrupted when extracellular Ca2+ was removed. The properties of Ca2+ oscillations in T lymphocytes suggest that they are mainly due to variations of Ca2+ influx, modulated by variations in [Ca2+]i.
Donnadieu
E
E
Laboratoire de Neurobiologie, Centre National de la Recherche Scientifique (CNRS) URA 295, Ecole Normale Supérieure, Paris, France.
Bismuth
G
G
Trautmann
A
A
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017252:CD3 Complex / Q000276:immunology / Q000502:physiology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002999:Clone Cells; D004533:Egtazic Acid / Q000494:pharmacology; D016257:Fura-2; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009991:Oscillometry; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013997:Time Factors; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D017252:CD3 Complex; D013729:Terpenes; D004533:Egtazic Acid; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2