Signal transduction in Jurkat T lymphocytes. Evidence for early Ca2+ movements between the cytoplasm and the nucleoplasm in activated cells.
Spatial analyses of the distribution of Ca2+ in resting and activated T and B lymphocytes have shown that the bulk of increased [Ca2+]i appears to be associated with the nuclear region. These observations suggest that Ca2+ is released from the perinuclear space or that it diffuses to the nucleoplasm, or both. We have used laser scanning confocal microscopy to assess whether cytoplasmic diffusion of Ca2+ could contribute to the rise in nuclear Ca2+. We found that the activation of individual Jurkat cells by use of an anti-Ti (beta-subunit) mAb induced a nucleus-associated increase in [Ca2+]i. In cells loaded with the InsP3 receptor antagonist heparin, the nuclear Ca2+ response was abolished but not the response to thapsigargin. Evidence for a cytoplasmic Ca2+ response was obtained by loading Jurkat cells with a cytoplasm-restricted Ca2+ probe (Calcium Green-1-Dextran). These observations suggested that a process of diffusion of cytoplasmic Ca2+ contributed to the rise of nuclear Ca2+ in Jurkat T cells. This interpretation was supported by the findings (1) that rapid scanning of thapsigargin-released Ca2+ showed an inverse relationship between the levels of cytoplasmic and nuclear Ca2+ and (2) that modulation of the external concentration of Ca2+ in thapsigargin-treated Jurkat cells showed a time-dependent decrease of fluorescence from the nucleoplasm that was reversed by raising the concentration of external Ca2+. We conclude that Ca2+ can rapidly diffuse between the cytoplasm and the nucleoplasm in activated Jurkat T lymphocytes and that hydrophilic Ca2+ probes largely partition to the nucleoplasm, thus giving rise to distorted nucleus-to-cytoplasm fluorescence ratios.
Gagné
D
D
Department of Biochemistry, Faculty of Medicine, University of Sherbrooke, Quebec, Canada.
Ahnadi
C E
CE
Martel
J
J
Payet
M D
MD
Dupuis
G
G
D002118:Calcium / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D017136:Ion Transport; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism* / Q000648:ultrastructure
D002118:Calcium