Figure 7.
BK channels control dendritic calcium spike propagation. A, Dendritic recording from a Purkinje cell filled with Alexa 594 and fluo-5F, recorded 140 μm from the soma. The image was taken with Alexa fluorescence. The stimulating electrode is drawn in blue. Scale bar, 50 μm. Inset, High-magnification image of the area of interest (dotted box) with five ROIs indicated. B, Maximum intensity projections of image stacks acquired during synaptically or current injection-evoked calcium spikes in control ACSF and 100 nm penitrem A. Scale bar, 20 μm. C, Calcium transients recorded from the five respective ROIs in the inset of A during synaptically evoked calcium spikes before (black) and after the BK channels (red) were blocked. D, The similarly selected five ROIs were averaged over three cells and normalized to the synaptic maximum in control ACSF. E, Calcium transients recorded from the five respective ROIs in the inset of A during current injection-evoked calcium spikes before (black) and after (red) the BK channels (were blocked. F, The similarly selected five ROIs were averaged over several cells and normalized to the synaptic maximum in control ACSF. Blocking the BK channels clearly improved the spatial spread of calcium spikes. Asterisks (in D, F) denote statistical significance (p < 0.05); error bars indicate SEM. G, The change in the fluorescence signal after penitrem A application was quantified in every ROI under control conditions (open circles) and BK channel block (filled circles). H, Dendritic calcium spikes (aligned at threshold and averaged) evoked with current injection before (black) and after penitrem A application (red). The bottom panel shows the second derivative of the calcium spikes, with a dotted vertical gray line indicating the threshold (see Materials and Methods).