Figure 5.

SK channels control the firing mode of a CLS cell. A, Representative traces from a CLS E-cell (0.3 nA current injection) showing a regularization of the firing pattern after EBIO (1 mm) and the subsequent conversion to a burst-firing mode after application of apamin (1 μm). B, Plotting the natural logarithm of the ISIs representing the traces in A shows a shift of the ISI distribution to longer intervals in response to EBIO along with a decrease in the spike count; the interval axis has been labeled in time units for clarity. The ISI distribution is shifted to shorter intervals and becomes clearly bimodal after apamin. The first peak of the apamin ISIH contains the burst spikes. C, Joint interval return maps showing randomly distributed points under baseline conditions confirm a nonbursting firing mode; the shortest ISIs are typically >10 ms. EBIO leads to an increase in ISI values and a regularization that is demonstrated by the presence of a single cluster of long ISIs. Apamin leads to a separation of the return map into a burst cluster (ISIs, <10 ms) and broadly distributed longer ISI returns representing variable interburst intervals as previously shown (Turner et al., 1996).