Mitogen-regulated Ca2+ current of T lymphocytes is activated by depletion of intracellular Ca2+ stores.
Stimulated influx of Ca2+ across the plasma membrane of T lymphocytes is an essential triggering signal for T-cell activation by antigen. Regulation of the T-cell Ca2+ conductance is not understood; conflicting evidence supports direct activation by inositol 1,4,5-trisphosphate (IP3) or by a signal generated by the depletion of intracellular Ca2+ stores. We have used the perforated-patch recording technique to compare the biophysical properties of Ca2+ currents activated by T-cell receptor stimulation and by thapsigargin, a Ca(2+)-ATPase inhibitor that depletes intracellular stores without generating IP3. Both currents are blocked by Ni2+, are inwardly rectifying, are highly Ca(2+)-selective, and exhibit voltage-independent gating with a unitary chord conductance of approximately 24 fS in isotonic Ca2+. Fluctuation analysis suggests that the underlying Ca2+ transporter is a channel rather than an iron carrier. Thus, in terms of ion permeation, gating, and unitary conductance, the Ca2+ current activated by thapsigargin is indistinguishable from the elicited by crosslinking of T-cell receptors. Moreover, the unitary Ca2+ conductance is > 100-fold smaller than that of previously described IP3-gated, Ca(2+)-permeable channels in T cells [Kuno, M. & Gardner, P. (1987) Nature (London) 326, 301-304]. These results demonstrate that mitogen-activated Ca2+ influx is controlled by the state of intracellular Ca2+ stores rather than by the direct action of IP3 on Ca2+ channels in the plasma membrane.
Department of Molecular and Cellular Physiology, Stanford University School of Medicine, CA 94305.
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Zweifach
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Lewis
D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D008934:Mitogens / Q000494:pharmacology*; D010835:Phytohemagglutinins / Q000494:pharmacology; D013601:T-Lymphocytes / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D008934:Mitogens; D010835:Phytohemagglutinins; D013729:Terpenes; D004533:Egtazic Acid; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium