A voltage-operable current is involved in Ca2+ entry in human lymphocytes whereas ICRAC has no apparent role.
Presently, it is thought that a non-voltage-gated current is responsible for activation-induced Ca2+ entry in nonelectrically excitable cells such as lymphocytes. However, it has also been proposed that the pathway instead involves a second messenger-regulated Ca2+ channel that is voltage operable, where "voltage operable" is defined as an intrinsic property of the channel protein(s) rather than a requirement of normal gating. To evaluate the contribution of these currents to activation-induced Ca2+ influx, each was examined with respect to its ability to account for Ca2+ influx as reported by Ca(2+)-sensitive dyes. We identified a set of reagents, nordihydroguaiaretic acid and various calmodulin inhibitors, that inhibits Ca2+ entry and blocks the voltage-operable current but leaves the non-voltage-gated current unaltered. Further-more, nordihydroguaiaretic acid inhibited Ca(2+)-dependent proliferation of mitogen-activated human peripheral blood mononuclear cells or Jurkat T cells and specifically blocked Ca(2+)-dependent interleukin 2 production by Jurkat T cells to a degree similar to the immunosuppressant drug cyclosporin A. We also identified compounds, amiloride and Mn2+, that block the non-voltage-gated current but have no effect on either the voltage-operable current or Ca2+ entry. Correspondingly, amiloride had no effect on Ca(2+)-dependent proliferation of Jurkat cells. These observations imply that blockade of the non-voltage-gated current does not block either Ca2+ entry or Ca(2+)-dependent lymphocyte proliferation, whereas blockade of the voltage-operable current does. The data suggest that the voltage-operable current may be a mediator of activation-induced Ca2+ entry in lymphocytes.
Densmore
J J
JJ
Department of Pathology, University of Virginia, Charlottesville 22908, USA.
Haverstick
D M
DM
Szabo
G
G
Gray
L S
LS
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002460:Cell Line; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000494:pharmacology; D005456:Fluorescent Dyes; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis; D015640:Ion Channel Gating; D007700:Kinetics; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000276:immunology / Q000502:physiology*; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology; D009637:Masoprocol / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D005456:Fluorescent Dyes; D007376:Interleukin-2; D001464:Barium; D008345:Manganese; D004533:Egtazic Acid; D019284:Thapsigargin; D009637:Masoprocol; D000584:Amiloride; D002118:Calcium