Effects of external Ca2+concentration on mEPSC bursts. (A) Summary data showing a significant mean mEPSC frequency increase and no significant mean amplitude change when increasing Cao from 1.5 to 3 mM. (B) Increasing Cao from 1.5 to 3 mM elicits bursting. Upper: IEI distributions shift from monoexponential in control conditions (1.5 mM Cao, blue; circles: experimental; continuous line: exponential fit with initial amplitude 0.34 event/bin, and time constant 8.5 s) to biexponential 10–15 min after shifting to 3 mM Cao (purple; fast component: amplitude 14 events/bin, time constant 66 ms; slow component: amplitude 1.7 event/bin, time constant 2.4 s). Bin durations are 50 ms up to 1.1 s, and 200 ms (with appropriate ordinate scaling) thereafter. Lower: Same data presented with logarithmic abscissa axis (bins: 0.2 log units). (C) Summary data showing a significant mean mEPSC frequency increase and a significant mean amplitude increase when raising Ko from 2.5 to 20 mM (3 mM Cao in both solutions). (D) Analysis of bursts elicited by elevating Ko, starting with 3 mM Cao. IEI histograms are displayed in linear (upper graph, with 50 ms bins) and logarithmic (lower graph, with 0.2 log unit bins) coordinates. Upper: In 20 mM Ko, the distribution follows a biexponential curve (black dots) with a fast component (amplitude 725 events/50 ms bin, time constant 10 ms) and a slow component (amplitude 78 events/50 ms bin, time constant 220 ms). Histogram resolution is enhanced to 10 ms/bin in the 0–100 ms range to better document the fast component (green line). Inset: fit of the initial part of the histogram with fast and slow exponential components in gray. Lower: The 3 Cao/20 Ko distribution (green) is clearly distinct from the 3 Cao/2.5 Ko distribution over a wide range of interval durations (purple), but it is not significantly different from the 1.5 Cao/20 Ko distribution (dashed red, from Fig. 1). Results are shown as mean ± SEM for n = 6 experiments from 4 animals comparing 1.5 Cao and 3 mM Cao (A and B), and n = 6 other experiments from 5 animals comparing 3 Cao/2.5 Ko with 3 Cao/20 Ko (C and D). P values indicate the results of paired t tests for cell data in A and C, and of Wilcoxon signed-rank test for first 50 ms bin in D. Dotted lines link individual cell data together in A and C.
Figure 2.

Effects of external Ca 2+ concentration on mEPSC bursts. (A) Summary data showing a significant mean mEPSC frequency increase and no significant mean amplitude change when increasing Cao from 1.5 to 3 mM. (B) Increasing Cao from 1.5 to 3 mM elicits bursting. Upper: IEI distributions shift from monoexponential in control conditions (1.5 mM Cao, blue; circles: experimental; continuous line: exponential fit with initial amplitude 0.34 event/bin, and time constant 8.5 s) to biexponential 10–15 min after shifting to 3 mM Cao (purple; fast component: amplitude 14 events/bin, time constant 66 ms; slow component: amplitude 1.7 event/bin, time constant 2.4 s). Bin durations are 50 ms up to 1.1 s, and 200 ms (with appropriate ordinate scaling) thereafter. Lower: Same data presented with logarithmic abscissa axis (bins: 0.2 log units). (C) Summary data showing a significant mean mEPSC frequency increase and a significant mean amplitude increase when raising Ko from 2.5 to 20 mM (3 mM Cao in both solutions). (D) Analysis of bursts elicited by elevating Ko, starting with 3 mM Cao. IEI histograms are displayed in linear (upper graph, with 50 ms bins) and logarithmic (lower graph, with 0.2 log unit bins) coordinates. Upper: In 20 mM Ko, the distribution follows a biexponential curve (black dots) with a fast component (amplitude 725 events/50 ms bin, time constant 10 ms) and a slow component (amplitude 78 events/50 ms bin, time constant 220 ms). Histogram resolution is enhanced to 10 ms/bin in the 0–100 ms range to better document the fast component (green line). Inset: fit of the initial part of the histogram with fast and slow exponential components in gray. Lower: The 3 Cao/20 Ko distribution (green) is clearly distinct from the 3 Cao/2.5 Ko distribution over a wide range of interval durations (purple), but it is not significantly different from the 1.5 Cao/20 Ko distribution (dashed red, from Fig. 1). Results are shown as mean ± SEM for n = 6 experiments from 4 animals comparing 1.5 Cao and 3 mM Cao (A and B), and n = 6 other experiments from 5 animals comparing 3 Cao/2.5 Ko with 3 Cao/20 Ko (C and D). P values indicate the results of paired t tests for cell data in A and C, and of Wilcoxon signed-rank test for first 50 ms bin in D. Dotted lines link individual cell data together in A and C.

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