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Vanadate Induces Calcium Signaling, Ca²⁺ Release-Activated Ca²⁺ Channel Activation, and Gene Expression in T Lymphocytes and RBL-2H3 Mast Cells Via Thiol Oxidation¹

Department of Physiology and Biophysics, University of California, Irvine, CA 92697

Using ratiometric Ca²⁺ imaging and patch-clamp measurement of Ca²⁺ channel activity, we investigated Ca²⁺ signaling induced by vanadium compounds in Jurkat T lymphocytes and rat basophilic leukemia cells. In the presence of external Ca²⁺, vanadium compounds produced sustained or oscillatory Ca²⁺ elevations; in nominally Ca²⁺-free medium, a transient Ca²⁺ rise was generated. Vanadate-induced Ca²⁺ signaling was blocked by heparin, a competitive inhibitor of the 1,4,5-inositol trisphosphate (IP₃) receptor, suggesting that Ca²⁺ influx is secondary to depletion of IP₃-sensitive Ca²⁺ stores. In Jurkat T cells, vanadate also activated the Ca²⁺-dependent transcription factor, NF-AT. Intracellular dialysis with vanadate activated Ca²⁺ influx through Ca²⁺ release-activated Ca²⁺ (CRAC) channels with kinetics comparable to those of dialysis with IP₃. Neither phosphatase inhibitors nor nonhydrolyzable nucleotide analogues modified CRAC channel activation. The action of vanadate, but not IP₃, was prevented by the thiol-reducing agent DTT. In addition, the activation of CRAC channels by vanadate was mimicked by the thiol-oxidizing agent chloramine T. These results suggest that vanadate enhances Ca²⁺ signaling via thiol oxidation of a proximal element in the signal transduction cascade.

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