SIGNALING BETWEEN INTRACELLULAR CA2-ACTIVATED CA2+ CHANNELS GENERATES[CA2+](I) OSCILLATIONS IN T-LYMPHOCYTES( STORES AND DEPLETION)

Stimulation through the antigen receptor (TCR) of T lymphocytes trigge rs cytosolic calcium ([Ca2+]i) oscillations that are critically depend ent on Ca2+ entry across the plasma membrane. We have investigated the roles of Ca2+ influx and depletion of intracellular Ca2+ stores in th e oscillation mechanism, using single-cell Ca2+ imaging techniques and agents that deplete the stores. Thapsigargin (TG; 5-25 nM), cyclopiaz onic acid (CPA; 5-20 muM), and tert-butylhydroquinone (tBHQ; 80-200 mu M), inhibitors of endoplasmic reticulum Ca2+-ATPases, as well as the C a2+ ionophore ionomycin (5-40 nM), elicit [Ca2+]i oscillations in huma n T cells. The oscillation frequency is approximately 5 mHz (for ATPas e inhibitors) to approximately 10 mHz (for ionomycin) at 22-24-degrees -C. The [Ca2+]i oscillations resemble those evoked by TCR ligation in terms of their shape, amplitude, and an absolute dependence on Ca2+ in flux. Ca2+-ATPase inhibitors and ionomycin induce oscillations only wi thin a narrow range of drug concentrations that are expected to cause partial depletion of intracellular stores. Ca2+-induced Ca2+ release d oes not appear to be significantly involved, as rapid removal of extra cellular Ca2+ elicits the same rate of [Ca2+]i decline during the risi ng and falling phases of the oscillation cycle. Both transmembrane Ca2 + influx and the content of ionomycin-releasable Ca2+ pools fluctuate in oscillating cells. From these data, we propose a model in which [Ca 2+]i oscillations in T cells result from the interaction between intra cellular Ca2+ stores and depletion-activated Ca2+ channels in the plas ma membrane.