FIGURE 4.

BI-1 increases the Ca²⁺ permeability of ER membranes. Thapsigargin (100 nm) was added at 1 min, and ionomycin (10 μm) was added either concomitantly with thapsigargin or at later time points (1–5 min at 1-min intervals). A, typical experiments showing initial peak calcium ([Ca²⁺]_c) elevations in Neo- and BI-1-expressing cells; four traces with ionomycin addition at different times are superimposed to facilitate comparison. B, ionomycin-releasable Ca²⁺ (expressed as a percentage of the initial peak [Ca²⁺]_c) is plotted as a function of time after thapsigargin addition in untransfected, Neo-, BI-1-, and CΔ-BI-1-transfected cells. Results shown in B represent the mean ± S.E. of four independent experiments (^*, p < 0.05 compared with the amount of [Ca²⁺]_c at 0 min). Tg, thapsigargin; Iono, ionomycin; UT, untransfected.