Slow Calcium-dependent Inactivation of Depletion-activated Calcium Current. STORE-DEPENDENT AND -INDEPENDENT MECHANISMS

• Published in: The Journal of biological chemistry Vol. 270; no. 24; pp. 14445 - 14451
• Main Authors: Zweifach, Adam, Lewis, Richard S.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16.06.1995; American Society for Biochemistry and Molecular Biology
• Subjects: Calcium - metabolism; Calcium Channel Blockers - metabolism; Cyclosporine - pharmacology; Ethers, Cyclic - pharmacology; Humans; Kinetics; Okadaic Acid; Phosphoprotein Phosphatases - antagonists & inhibitors; Tacrolimus - pharmacology; Tumor Cells, Cultured
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.24.14445

Feedback regulation of Ca2+ release-activated Ca2+ (CRAC) channels was studied in Jurkat leukemic T lymphocytes using whole cell recording and [Ca2+]i measurement techniques. CRAC channels were activated by passively depleting intracellular Ca2+ stores in the absence of extracellular Ca2+. Under conditions of moderate intracellular Ca2+ buffering, elevating [Ca2+]o to 22 mM initiated an inward current through CRAC channels that declined slowly with a half-time of ~30 s. This slow inactivation was evoked by a rise in [Ca2+]i, as it was effectively suppressed by an elevated level of EGTA in the recording pipette that prevented increases in [Ca2+]i. Blockade of Ca2+ uptake into stores by thapsigargin with or without intracellular inositol 1,4,5-trisphosphate reduced the extent of slow inactivation by ~50%, indicating that store refilling normally contributes significantly to this process. The store-independent (thapsigargin-insensitive) portion of slow inactivation was largely prevented by the protein phosphatase inhibitor, okadaic acid, and by a structurally related compound, 1-norokadaone, but not by calyculin A nor by cyclosporin A and FK506 at concentrations that fully inhibit calcineurin (protein phosphatase 2B) in T cells. These results argue against the involvement of protein phosphatases 1, 2A, 2B, or 3 in store-independent inactivation. We conclude that calcium acts through at least two slow negative feedback pathways to inhibit CRAC channels. Slow feedback inhibition of CRAC current is likely to play important roles in controlling the duration and dynamic behavior of receptor-generated Ca2+ signals.