The cytosolic free calcium in anti-mu-stimulated human B cells is derived partly from extracellular medium and partly from intracellular stores.
The inositol phospholipid metabolism and the increase in cytosolic free Ca2+ concentration ([Ca2+]i) into the cell are recognized as two important events in the anti-mu-induced B cell activation. The anti-mu stimulation caused the [3H]inositol incorporation and also a rapid increase in [Ca2+]i from 85 nM to 285 nM. This signal returned to baseline a few minutes after stimulation. By using the fluorescent indicator quin-2 we demonstrated that this [Ca2+]i uptake was derived part from extracellular medium and part from intracellular stores. Both EGTA (a calcium chelator) and TMB.8 (a drug which interferes with Ca2+ sequestration by smooth endoplasmic reticulum) partially suppressed the intracellular Ca2+ uptake and were fully inhibitory when added together. The role of Ca2+ from intracellular stores may also be evidenced in calcium-free experiments, or in permeabilized experiments using exogenous inositol 1,4,5-trisphosphate (IP3, the putative mobilizer of intracellular Ca2+). Preventing the increase in [Ca2+]i also prevents the apparition of early activation makers. These results are consistent with the hypothesis that the Ca2+ increase in B cells stimulated by anti-mu is caused by the generation of IP3 during the phosphatidyl-inositol metabolism and also by the entry of extracellular Ca2+ through the plasma membrane.
Dugas
B
B
Departement des Biotechnologies, Roussel-UCLAF, Romainville, France.
Calenda
A
A
Delfraissy
J F
JF
Vazquez
A
A
Bach
J F
JF
Galanaud
P
P
D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology; D007424:Intracellular Fluid / Q000378:metabolism; D008213:Lymphocyte Activation; D010716:Phosphatidylinositols / Q000378:metabolism
D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D007075:Immunoglobulin M; D010716:Phosphatidylinositols; C044203:anti-IgM; D002118:Calcium