Increasing the external K+concentration elicits mEPSC bursts. (A) mEPSCs under control conditions (1.5 mM Cao, 2.5 mM Ko saline, containing tetrodotoxin, gabazine, and APV). Upper: Example trace. Middle: mEPSC frequency remains small and stable over a period of 20 min (time bins: 30 s duration). Lower: Mean mEPSC frequency ± SEM, over 30 s long time bins. (B) Effect of elevating Ko. Upper: Example trace in 20 mM Ko, with individual mEPSC burst enlarged. Middle: mEPSC frequency shows large, slow fluctuations in individual recordings, and large cell-to-cell variability. Time 0 marks the transition to the higher Ko. Lower: Plotting mean mEPSC frequency as a function of time (error bars: ± SEM) reveals a slow increase in the higher Ko solution (green: 30 s bins; black: 5 min bins). (C) Summary plots comparing mEPSC frequencies and amplitudes in 2.5 mM Ko (blue) and 10–15 min after switching to 20 mM Ko (green). (D) Cumulative amplitude distributions for 2.5 mM Ko and 20 mM Ko, showing a stronger contribution of large amplitude events in 20 mM Ko. (E) IEI histograms in 2.5 mM Ko and in 20 mM Ko. Histograms reflect 5 min long data taken either in control saline (blue), or 10–15 min after switching to 20 mM Ko (green). The upper plot uses linear coordinates. Circles and associated error bars are calculated for 50 ms bins. For 20 mM Ko data, data are displayed with 10 ms resolution up to 100 ms to highlight the initial part of the histogram (green trace). In 2.5 mM Ko, the interval distribution displays a single exponential component (blue trace) with initial amplitude 9 events/50 ms bin and time constant 370 ms. In 20 mM Ko, IEI distribution is fitted with a double exponential (black dots), where the fast component has an amplitude of 204 events/50 ms bin and a time constant of 18 ms, and the slow component has an amplitude of 44 events/50 ms bin and a time constant of 393 ms (inset: fit of the initial part of the histogram with fast and slow exponential components in gray). The lower plot shows the same data with logarithmic abscissa (bins: 0.2 log unit). P values indicate paired t tests for cell data in C, Kolmogorov-Smirnov test in D, and Wilcoxon signed-rank test for first 50 ms bin in E. Dotted lines link individual cell data together in C. Number of independent experiments: n = 4 cells from 2 animals in A; n = 8 cells from 4 animals in B–E.
Figure 1.

Increasing the external K + concentration elicits mEPSC bursts. (A) mEPSCs under control conditions (1.5 mM Cao, 2.5 mM Ko saline, containing tetrodotoxin, gabazine, and APV). Upper: Example trace. Middle: mEPSC frequency remains small and stable over a period of 20 min (time bins: 30 s duration). Lower: Mean mEPSC frequency ± SEM, over 30 s long time bins. (B) Effect of elevating Ko. Upper: Example trace in 20 mM Ko, with individual mEPSC burst enlarged. Middle: mEPSC frequency shows large, slow fluctuations in individual recordings, and large cell-to-cell variability. Time 0 marks the transition to the higher Ko. Lower: Plotting mean mEPSC frequency as a function of time (error bars: ± SEM) reveals a slow increase in the higher Ko solution (green: 30 s bins; black: 5 min bins). (C) Summary plots comparing mEPSC frequencies and amplitudes in 2.5 mM Ko (blue) and 10–15 min after switching to 20 mM Ko (green). (D) Cumulative amplitude distributions for 2.5 mM Ko and 20 mM Ko, showing a stronger contribution of large amplitude events in 20 mM Ko. (E) IEI histograms in 2.5 mM Ko and in 20 mM Ko. Histograms reflect 5 min long data taken either in control saline (blue), or 10–15 min after switching to 20 mM Ko (green). The upper plot uses linear coordinates. Circles and associated error bars are calculated for 50 ms bins. For 20 mM Ko data, data are displayed with 10 ms resolution up to 100 ms to highlight the initial part of the histogram (green trace). In 2.5 mM Ko, the interval distribution displays a single exponential component (blue trace) with initial amplitude 9 events/50 ms bin and time constant 370 ms. In 20 mM Ko, IEI distribution is fitted with a double exponential (black dots), where the fast component has an amplitude of 204 events/50 ms bin and a time constant of 18 ms, and the slow component has an amplitude of 44 events/50 ms bin and a time constant of 393 ms (inset: fit of the initial part of the histogram with fast and slow exponential components in gray). The lower plot shows the same data with logarithmic abscissa (bins: 0.2 log unit). P values indicate paired t tests for cell data in C, Kolmogorov-Smirnov test in D, and Wilcoxon signed-rank test for first 50 ms bin in E. Dotted lines link individual cell data together in C. Number of independent experiments: n = 4 cells from 2 animals in A; n = 8 cells from 4 animals in B–E.

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