Figure 1.

(A) Pseudocolored ratiometric images of an albino Xenopus oocyte preloaded with Fura-2 after injection at t = 0 of 14 nl of acid extract prepared from the equivalent of 5,000 thapsigargin-treated Jurkat cells. Increases in the 340/380 nm ratio relative to those at the time of injection are shown. Extracellular Ca²⁺ was 5 mM. The asterisk in the first frame denotes the point of injection. Data shown are representative of injections of 15 independent preparations. (B) Pseudocolored images after injection of an acid extract corresponding to approximately 200,000 pmr1 yeast cells. Data shown are representative of injections of 25 independent preparations. (C) Increases in fluorescence ratio for extracts prepared from: (a) untreated Jurkat cells; (b) Jurkat cells in which thapsigargin was added immediately before acid extraction; (c) Jurkat cells extracted 15 min after thapsigargin treatment; (d) wild-type yeast; (e) pmr1 yeast; (f) pmr1 yeast, but the oocytes were bathed in a medium containing 5 mM EGTA; (g) pmr1 yeast, but the extract was applied extracellularly; (h) pmr1 yeast, but the extract was coinjected with heparin (3,000 Da) at a final cytoplasmic concentration estimated to be 200 μM. The data are means of from 3 to 10 replicates. Standard deviations are shown. (D) Increases in fluorescence as a function of increasing concentrations of the yeast extract in the absence (■) and presence (Δ) of 2 mM LaCl₃. The data in C and D refer to the maximal R/R_o averaged over a 500 × 700-μm area containing ≈45% of the oocyte including the injection site. (E) Time course of ratiometric increases shown in A for a series of 80-μm wide segments spanning the oocyte from the point of injection (leftmost curve) and progressing to the opposite side (rightmost curve). Measurements are from the oocyte’s plasma membrane at the point of penetration to the center of each segment. (F) Times to reach a fluorescence ratio of 1.4 (shown as boxes in E) for each of the segments depicted in E. Comparable patterns were detected in multiple independent preparations from Jurkat (■) and pmr1 yeast (data not shown). Also shown (□) is the simulated progression of [Ca²⁺]_i increases due to a diffusible CIF (19).