Figure 2.

Ca²⁺ dependence of uptake by the TG-insensitive Ca²⁺ store. (A) Cells were stimulated as in Fig. 1 B to load the TG- insensitive store. The loading period was terminated by removing extracellular Ca²⁺, and 4 μM ionomycin was added subsequently to assay store content. The responses of three single cells from one experiment are superimposed. (B) Store content plotted as a function of the average magnitude of the Ca²⁺ plateau for individual cells. Three measures of store content are plotted: the peak [Ca²⁺]_i (•), the maximum rate of [Ca²⁺]_i rise (○), and the integral of released Ca²⁺ (corrected for clearance rate, see Materials and Methods; □) in response to ionomycin. Results were obtained from 964 cells in 11 experiments and binned into 100-nM intervals of [Ca²⁺]_i.