T cell receptor-mediated Ca2+ signaling: release and influx are independent events linked to different Ca2+ entry pathways in the plasma membrane.
In this study, we showed that cross-linking CD3 molecules on the T cell surface resulted in Ca2+ release from the intracellular stores followed by a sustained Ca2+ influx. Inhibition of release with TMB-8 did not block the influx. However, inhibition of phospholipase C activity suppressed both Ca2+ release and influx. Once activated, the influx pathway remained open in the absence of further hydrolysis of PIP2. Thapsigargin, a microsomal Ca(2+)-ATPase inhibitor, stimulated Ca2+ entry into the cells by a mechanism other than emptying Ca2+ stores. In addition, Ca2+ entry into the Ca(2+)-depleted cells was stimulated by low basal level of cytosolic Ca2+, not by the emptying of intracellular Ca2+ stores. Both the Ca2+ release and influx were dependent on high and low concentrations of extracellular Ca2+. At low concentrations, Mn2+ entered the cell through the Ca2+ influx pathway and quenched the sustained phase of fluorescence; whereas, at higher Mn2+ concentration both the transient and the sustained phases of fluorescence were quenched. Moreover, Ca2+ release was inhibited by low concentrations of Ni2+, La3+, and EGTA, while Ca2+ influx was inhibited by high concentrations. Thus, in T cells Ca2+ influx occurs independently of IP3-dependent Ca2+ release. However, some other PIP2 hydrolysis-dependent event was involved in prolonged activation of Ca2+ influx. Extracellular Ca2+ influenced Ca2+ release and influx through the action of two plasma membrane Ca2+ entry pathways with different pharmacological and biochemical properties.
Chakrabarti
R
R
Department of Cell Biology and Human Anatomy, University of California, School of Medicine, Davis 95616-8643, USA.
Chang
J Y
JY
Erickson
K L
KL
D000818:Animals; D017252:CD3 Complex / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D006868:Hydrolysis; D007424:Intracellular Fluid / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D007811:Lanthanum / Q000494:pharmacology; D008345:Manganese / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009532:Nickel / Q000494:pharmacology; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D017252:CD3 Complex; D015220:Calcium Channels; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D011948:Receptors, Antigen, T-Cell; D013729:Terpenes; D008345:Manganese; D019284:Thapsigargin; D007811:Lanthanum; D009532:Nickel; D002118:Calcium