Ca2+ influx in human T lymphocytes is induced independently of inositol phosphate production by mobilization of intracellular Ca2+ stores. A study with the Ca2+ endoplasmic reticulum-ATPase inhibitor thapsigargin.
Thapsigargin (TG), a sesquiterpene lactone and non-phorbol 12-myristate 13-acetate tumor promoter, stimulates a rapid increase in intracellular free Ca2+ [( Ca2+]i) in human T lymphocytes clone P28. The [Ca2+]i response to TG is sustained in the presence of 1 mM extracellular Ca2+, while it becomes transient in Ca2(+)-free medium suggesting that TG activates both the release of Ca2+ from intracellular stores and the entry of Ca2+ from extracellular spaces. TG-induced Ca2+ influx is completely abolished after cell depolarization caused by increased extracellular concentrations of K+. The rise in [Ca2+]i stimulated by TG occurs in the absence of detectable production of inositol phosphates. Moreover, TG does not alter the early biochemical events of T cell activation triggered through the CD2 or the CD3 T cell antigens. Indeed, both inositol phosphate production and intracellular pH increase induced by specific monoclonal antibodies (mAb) remain unchanged after TG treatment. These data suggest that in human T lymphocytes TG releases Ca2+ from an intracellular pool by a mechanism which is independent of the phospholipase C metabolic pathway. Preincubation with TG of T cell clone P28 empties both the CD2 and the CD3-sensitive intracellular Ca2+ pool(s). Conversely, prestimulation of T cell clone P28 by CD3 or CD2-specific mAb inhibits the Ca2(+)-mobilizing effect of TG. Thus it appears that TG and CD2- or CD3-specific mAb mobilize Ca2+ from common Ca2+ pool(s). Taken together, these results demonstrate that Ca2+ influx in human T cells may be linked to mobilization of intracellular Ca2+ pools and by a mechanism independent of phosphoinositide hydrolysis. They further indicate that the release of intracellular Ca2+ pool(s) may play a major role in the opening of cell membrane Ca2+ channels observed during the CD2- or CD3-induced stimulation of human T lymphocytes.
Laboratoire d'Immunologie Cellulaire et Tissulaire, CNRS URA 186, CERVI, Paris, France.
H
H
Gouy
D
D
Cefai
S B
SB
Christensen
P
P
Debré
G
G
Bismuth
D000911:Antibodies, Monoclonal / Q000276:immunology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology / Q000502:physiology; D018801:CD2 Antigens; D017252:CD3 Complex; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002999:Clone Cells; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D000939:Epitopes; D005455:Fluorescent Antibody Technique; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007295:Inositol Phosphates / Q000096:biosynthesis*; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000502:physiology; D011971:Receptors, Immunologic / Q000276:immunology / Q000502:physiology; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte; D018801:CD2 Antigens; D017252:CD3 Complex; D000939:Epitopes; D007295:Inositol Phosphates; D011948:Receptors, Antigen, T-Cell; D011971:Receptors, Immunologic; D013729:Terpenes; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium