Fig. 5
Changes in membrane excitability and HCN channel activity contribute to PIF in vitro. a Voltage traces from an representative single-event conductance-clamp experiment at a Ge value that generated a spike from excitation alone (black). The same protocol performed with an inhibition time at –4 ms rTD (red) also produced a spike but occurred earlier and with a lower voltage threshold (Vt, right). Scale bars: 20 mV, 2 ms (left) and 0.5 ms (right). b Quantification of the relative change of spike voltage threshold as a function of ΔBest rTD. c Example traces from a voltage-clamp recording where the voltage command (top) started as an IPSP waveform, but then stepped to a suprathreshold value (3 ms duration) after a particular time (IPSP time). The resulting current response (bottom) shows a transient inward current that reflects sodium currents associated with an AP. Traces at an IPSP time of 2.5 ms are highlighted in black. d Top: mean AP current amplitude as a function of IPSP time for the recording in c. Inverted IPSP time course (green) is overlaid to compare with the time course of AP current modulation. Bottom: box plot shows the median and first/third quartiles (whiskers denote the range) of the distribution of AP boost for all recordings (open markers). e, f Example normalized traces (e) and quantification (f) of EPSP and IPSP decay kinetics before and after HCN channel blocker (ZD) wash-in. Scale bars (e): 2 ms (top) and 5 ms (bottom). g Example traces from a single-event conductance-clamp PIF protocol before (left) and after (right) ZD wash-in. Scale bar: 20 mV, 2 ms. h Average PIF functions for before (gray) and after (dotted black) ZD wash-in. i Population maximum inhibitory boost (left) and PIF function half-width (right) compared between control and after ZD wash-in. Light and bold lines and markers in f, i indicate individual experiments and population averages, respectively
