Ion channels, Ca2+ signaling, and reporter gene expression in antigen-specific mouse T cells.

Whole cell recordings were performed in parallel with measurements of intracellular Ca2+ ([Ca2+]i) and gene expression using the murine T cell hybridoma, B3Z, a cell line stably infected with a lacZ reporter gene, driven by the minimal IL-2 promoter (NF-AT, nuclear factor of activated T cells). The physiologic roles of ion channels in B3Z cells were investigated by correlating the pharmacology of channel block with [Ca2+]i, and expression of lacZ. In B3Z cells and activated human T cells, the major component of voltage-gated K+ (K(V)) current had biophysical and pharmacologic properties associated with type n channels encoded by Kv1.3; a minor K(V) component was charybdotoxin (CTX) resistant. Ca2+-activated K+ (K(Ca)) current was sensitive to CTX, but not to margatoxin (MgTX). Inwardly rectifying K+ (K(IR)) current was blocked completely by 200 microM of Ba2+. Outwardly rectifying Cl- currents were induced by cell swelling. An inwardly rectifying Ca2+ current (I(CRAC)) was activated by dialyzing the cell with 10 mM EGTA and 10 microM IP3. CTX reduced thapsigargin-stimulated [Ca2+]i signaling and gene expression by approximately 25%. Although the thapsigargin-stimulated [Ca2+]i signal was resistant to complete inhibition by K+ channel blockers, it was very sensitive to the K+ diffusion potential and Cl- removal, suggesting that drug-resistant K+ channels and perhaps Cl- channels can maintain a sufficiently negative membrane potential to drive Ca2+ influx. Neither [Ca2+]i signaling nor gene expression induced by stimulation of the CD3-epsilon subunit of the TCR was inhibited by ion channel blockers used in this study. We conclude that several channel types can contribute to maintenance of Vm, Ca2+ signals, and gene expression.