Mouse chromaffin cells in slices show a biphasic rise of ΔC_exo with increasing duration of Ca²⁺ current injection. A(top), The filled circles represent pooled data of 10 slice cells with ΔC_exoestimated by approach 2 in Materials and Methods. For convenience these data were fitted by a double exponential (solid line). The slow secretory component, however, did not saturate with our maximal stimuli. The empty squares plot the ΔC_exo versus pulse duration data of 20 isolated mouse chromaffin cells. No clear separation into two secretory components was observed. Experiments were carried out as described above (pipette solution B), except that an external [Ca²⁺] of 10 mm was used. The ΔC_exo versus pulse duration data obtained from isolated rat chromaffin cells by Horrigan and Bookman (1994) are displayed for comparison (diamonds).Bottom, A plot of Q_Ca versus pulse duration demonstrates that for short depolarizations,Q_Ca rises linearly with increasing pulse duration for both preparations. Furthermore, it shows that theQ_Ca values of slice (filled circles) and isolated (empty squares) cells more or less overlap for short pulses. B, The same ΔC_exo data as in Figure 3Awere related to their corresponding Ca²⁺ current integrals (Q_Ca). The filled circlesrepresent pooled and binned data from slice experiments. The data for isolated mouse cells are displayed as empty circles. Note that the ΔC_exo–Q_Carelation is displayed only for small Q_Cavalues (where a difference between both preparations was observed). Thenumbers of data points per bin are printedabove and below the graph for slice and isolated chromaffin cells, respectively. The vertical bars are SEM for ΔC_exo values, whereas the horizontal bars indicate SD of binnedQ_Ca values. C, The different lines represent ΔC_exo data from the same experiments in slices as those analyzed in Figure 3A, estimated by three different approaches (see Materials and Methods and Fig. 2A). The dashed line(approach 3 in Materials and Methods) represents early ΔC_exo estimates, whereas the solid line (approach 2) and the dotted line (approach 1) result from later measurements after the pulse. This figure demonstrates that all three approaches give quite similar ΔC_exo estimates at short depolarizations. The discrepancy between the estimates at 200 and 300 msec pulse durations is most likely attributable to some “post-pulse” secretion.