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) ap pears to be associated with the nuclear region. These observations sug gest that Ca2+ is released from the perinuclear space or that it diffu ses to the nucleoplasm, or both. We have used laser scanning confocal microscopy to assess whether cytoplasmic, diffusion of Ca2+ could cont ribute to the rise in nuclear Ca2+. We found that the activation of in dividual Jurkat cells by use of an anti-Ti (beta-subunit) mAb induced a nucleus-associated increase in [Ca2+](i). In cells loaded with the I nsP3 receptor antagonist heparin, the nuclear Ca2+ response was abolis hed but not the response to thapsigargin. Evidence for a cytoplasmic C a2+ response was obtained by loading Jurkat cells with a cytoplasm-res tricted Ca2+ probe (Calcium Green-1-Dextran). These observations sugge sted that a process of diffu sion of cytoplasmic Ca2+ contributed to t he rise of nuclear Ca2+ in Jurkat T cells. This interpretation was sup ported by the findings (1) that rapid scanning of thapsigargin-release d Ca2+ showed an inverse relationship between the levels of cytoplasmi c and nuclear Ca2+ and (2) that modulation of the external concentrati on of Ca2+ in thapsigargin-treated Jurkat cells showed a time-dependen t decrease of fluorescence from the nucleoplasm that was reversed by r aising the concentration of external Ca2+. We conclude that Ca2+ can r apidly diffuse between the cytoplasm and the nucleoplasm in activated Jurkat T lymphocytes and that hydrophilic Ca2+ probes largely partitio n to the nucleoplasm, thus giving rise to distorted nucleus-to-cytopla sm fluorescence ratios.