Rapid inactivation of depletion-activated calcium current (ICRAC) due to local calcium feedback.
Rapid inactivation of Ca2+ release-activated Ca2+ (CRAC) channels was studied in Jurkat leukemic T lymphocytes using whole-cell patch clamp recording and [Ca2+]i measurement techniques. In the presence of 22 mM extracellular Ca2+, the Ca2+ current declined with a biexponential time course (time constants of 8-30 ms and 50-150 ms) during hyperpolarizing pulses to potentials more negative than -40 mV. Several lines of evidence suggest that the fast inactivation process is Ca2+ but not voltage dependent. First, the speed and extent of inactivation are enhanced by conditions that increase the rate of Ca2+ entry through open channels. Second, inactivation is substantially reduced when Ba2+ is present as the charge carrier. Third, inactivation is slowed by intracellular dialysis with BAPTA (12 mM), a rapid Ca2+ buffer, but not by raising the cytoplasmic concentration of EGTA, a slower chelator, from 1.2 to 12 mM. Recovery from fast inactivation is complete within 200 ms after repolarization to -12 mV. Rapid inactivation is unaffected by changes in the number of open CRAC channels or global [Ca2+]i. These results demonstrate that rapid inactivation of ICRAC results from the action of Ca2+ in close proximity to the intracellular mouths of individual channels, and that Ca2+ entry through one CRAC channel does not affect neighboring channels. A simple model for Ca2+ diffusion in the presence of a mobile buffer predicts multiple Ca2+ inactivation sites situated 3-4 nm from the intracellular mouth of the pore, consistent with a location on the CRAC channel itself.
Zweifach
A
A
Department of Molecular and Cellular Physiology, Stanford University School of Medicine, California 94305, USA.
Lewis
R S
RS
D001464:Barium / Q000493:pharmacokinetics; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D015536:Down-Regulation / Q000502:physiology*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology; D006801:Humans; D007700:Kinetics; D018408:Patch-Clamp Techniques; D013601:T-Lymphocytes / Q000502:physiology; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D002614:Chelating Agents; D001464:Barium; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium