Inhibition of Ca2+influx by LrB in Jurkat T cells. (A) Representative images were taken in the presence of Ca2+-free extracellular solution (left) and 6 minutes after 2 mM Ca2+ was added (right) with the intracellular Ca2+ store depleted by 10 μM CPA. (B) and (C) Representative images illustrate that 10 and 30 μM LrB markedly decreased the intracellular Ca2+ response induced by 2 mM extracellular Ca2+ in CPA-treated Jurkat T cells. (D) Representative traces show the effect of LrB on store depletion-induced Ca2+ influx. Each trace represents averaged F340/F380 ratio from about 400 Jurkat T cells. The ratio traces in the presence of 0, 10 and 30 μM LrB are color-coded with black, red and green, respectively. The first [Ca2+]i peak presents a rapid Ca2+ rise evoked by 10 μM CPA in 0 Ca2+ in extracellular solution, and the second [Ca2+]i peak illustrates the sustained store depletion-induced Ca2+ influx with an addition of 2 mM Ca2+ in the absence and presence of different concentrations of LrB. The second peak is fitted with a single exponential function to calculate the rise time constant of store depletion-induced Ca2+ influx. (E) Statistical data summarizes the net changes in F340/F380 ratios induced by 2 mM extracellular Ca2+, ***P < 0.001. (F) Statistical data illustrates the rise time constant of store depletion-induced Ca2+ influx in the presence of 0 (Ctl), 10 and 30 μM LrB, *P < 0.05, **P < 0.01.