Single channel properties and regulated expression of Ca(2+) release-activated Ca(2+) (CRAC) channels in human T cells.
Although the crucial role of Ca(2+) influx in lymphocyte activation has been well documented, little is known about the properties or expression levels of Ca(2+) channels in normal human T lymphocytes. The use of Na(+) as the permeant ion in divalent-free solution permitted Ca(2+) release-activated Ca(2+) (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 Ca(2+) store depletion resulted in the opening of 41-pS CRAC channels characterized by high open probabilities, voltage-dependent block by extracellular Ca(2+) in the micromolar range, selective Ca(2+) permeation in the millimolar range, and inactivation that depended upon intracellular Mg(2+) ions. The number of CRAC channels per cell increased greatly from approximately 15 in resting T cells to approximately 140 in activated T cells. Treatment with the phorbol ester PMA also increased CRAC channel expression to approximately 60 channels per cell, whereas the immunosuppressive drug cyclosporin A (1 microM) suppressed the PHA-induced increase in functional channel expression. Capacitative Ca(2+) 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 Ca(2+) influx in human resting T cells, and that the expression of CRAC channels increases approximately 10-fold during activation, resulting in enhanced Ca(2+) signaling.
Fomina
A F
AF
Department of Physiology and Biophysics, University of California Irvine, Irvine, California 92697-4561, USA.
Fanger
C M
CM
Kozak
J A
JA
Cahalan
M D
MD
D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000276:immunology*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D019169:Jurkat Cells; D007700:Kinetics; D008213:Lymphocyte Activation / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010835:Phytohemagglutinins / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013601:T-Lymphocytes / Q000502:physiology*; D015854:Up-Regulation / Q000187:drug effects / Q000276:immunology
D015220:Calcium Channels; D002614:Chelating Agents; D010835:Phytohemagglutinins; D004533:Egtazic Acid; D012964:Sodium; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium