Calcium-dependent enhancement of depletion-activated calcium current in Jurkat T lymphocytes.
We have obtained evidence that the Ca(2+)-selective current activated by Ca2+ store depletion (Ca2+ release-activated Ca2+ current; Icrac) in Jurkat T lymphocytes is augmented in a time-dependent manner by Ca2+ itself. Whole cell patch clamp experiments employed high cytosolic Ca(2+)-buffering conditions to passively deplete Ca2+ stores. Rapidly switching to nominally Ca(2+)-free extracellular buffer instantaneously reduced Icrac measured at -100 mV to leak current level. Unexpectedly, readmission of 2 mM Ca2+ instantaneously restored only 38 +/- 5% (mean +/- SEM, n = 9) of the full Icrac amplitude. The remainder reappeared in a monotonic time-dependent manner over 10 to 20 sec. Rapid vs. slow intracellular Ca2+ chelators did not alter this process, and inorganic Icrac blockers did not regenerate it, arguing against an intracellular site of action. The effect was specific to Ca2+: introduction of the permeant ions, Ba2+ or Sr2+, failed to invoke time-dependent Icrac reappearance. Moreover, equimolar substitution of Ba2+ for Ca2+ initially produced Ba2+ current of similar magnitude to the full Ca2+ current, but the Ba2+ current decayed monotonically to < 50% of its initial amplitude in < 20 sec. Conversely, return to Ca2+ produced a time-dependent increase in Icrac to its larger Ca2+ permeation level. Thus Ca2+ appears to selectively promote a reversible transition of Icrac that results in larger current flux, and at least partially explains the selectivity of this current for Ca2+ over other divalent ions.
Christian
E P
EP
Department of Pharmacology, Zeneca Pharmaceuticals, Wilmington, DE 19850, USA.
Spence
K T
KT
Togo
J A
JA
Dargis
P G
PG
Patel
J
J
D000818:Animals; D001464:Barium / Q000378:metabolism; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D002463:Cell Membrane Permeability; D017136:Ion Transport; D007700:Kinetics; D008564:Membrane Potentials; D051381:Rats; D013601:T-Lymphocytes / Q000378:metabolism*
D015220:Calcium Channels; D001464:Barium; D002118:Calcium