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Published online 18 September 2000. doi:10.1083/jcb.150.6.1435
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© The Rockefeller University Press, 0021-9525/2000//1435 $5.00
The Journal of Cell Biology, Volume 150, Number 6, , 2000 1435-1444

Original Article

Single Channel Properties and Regulated Expression of Ca2+ Release-Activated Ca2+ (Crac) Channels in Human T Cells



Alla F. Fominaa, Christopher M. Fangera, J. Ashot Kozaka, and Michael D. Cahalana

a Department of Physiology and Biophysics, University of California Irvine, Irvine, California 92697-4561
Department of Physiology and Biophysics, University of California Irvine, Irvine, CA 92697-4561.(949) 824-3143(949) 824-7776

Although the crucial role of Ca2+ influx in lymphocyte activation has been well documented, little is known about the properties or expression levels of Ca2+ channels in normal human T lymphocytes. The use of Na+ as the permeant ion in divalent-free solution permitted Ca2+ release-activated Ca2+ (CRAC) channel activation, kinetic properties, and functional expression levels to be investigated with single channel resolution in resting and phytohemagglutinin (PHA)-activated human T cells. Passive Ca2+ store depletion resulted in the opening of 41-pS CRAC channels characterized by high open probabilities, voltage-dependent block by extracellular Ca2+ in the micromolar range, selective Ca2+ permeation in the millimolar range, and inactivation that depended upon intracellular Mg2+ ions. The number of CRAC channels per cell increased greatly from ~15 in resting T cells to ~140 in activated T cells. Treatment with the phorbol ester PMA also increased CRAC channel expression to ~60 channels per cell, whereas the immunosuppressive drug cyclosporin A (1 µM) suppressed the PHA-induced increase in functional channel expression. Capacitative Ca2+ influx induced by thapsigargin was also significantly enhanced in activated T cells. We conclude that a surprisingly low number of CRAC channels are sufficient to mediate Ca2+ influx in human resting T cells, and that the expression of CRAC channels increases ~10-fold during activation, resulting in enhanced Ca2+ signaling.

Key Words: T lymphocyte • Ca2+ channel • CRAC channel • T cell activation • Ca2+ signaling

© 2000 The Rockefeller University Press

Abbreviations used in this paper: BAPTA, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; [Ca2+]i, intracellular calcium concentration; CRAC, Ca2+ release-activated Ca2+; CsA, cyclosporin A; HEDTA, N-hydroxyethyl-ethylenediamine-triacetic acid; KCa, Ca2+-activated K+; NF-AT, nuclear factor of activated T cells; NMDG+, N-methyl D-glucamine; PHA, phytohemagglutinin; TCR, T cell receptor; Tg, thapsigargin.


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