Fig. 3.

Na currents, inactivation, and firing. a Transient, persistent, and resurgent tetrodotoxin-sensitive Na current evoked in a cerebellar nuclear cell acutely isolated from a ~2-week-old mouse. Currents were evoked by the voltage protocol shown. Responses to depolarizing and repolarizing steps are expanded in the insets. Red trace indicates steps to –30 mV. b Top panel Tetrodotoxin-sensitive Na currents evoked by step depolarizations from −60 to 0 mV applied at 20 Hz (10 stimuli), and interrupted by a 250-ms step to –60, –70, or –80 mV. After this interval, three depolarizations are applied at 100 Hz to simulate a burst of action potentials. The first current evoked after the 250-ms pause is expanded in the inset. Bottom panel Mean currents evoked by this protocol in five cells. During the 20-Hz train, Na channels inactivate by about 50%, and the availability of Na channels after the pause depends on the voltage during the interval. Data from [44], reproduced with permission. c Spontaneous action potentials with no holding current (left) and their derivatives (right) in an isolated cerebellar nuclear cell after a period of voltage clamp at –68 mV. Note the decrease in dV/dt over time, reflecting the decreasing availability of Na channels. Data from [10], reproduced with permission. d Left Action potentials and IPSPs evoked at 100 Hz in a cerebellar nuclear neuron in a slice (33°C). No holding current. Right Firing rate after the IPSPs plotted against the rate before the IPSPs, for 13 cells recording in the whole-cell configuration and 16 cells recorded in the perforated-patch configuration with gramicidin. Red symbols indicate the means of the two data sets. Solid line is a linear fit to the data, with a fitted slope of 1.0 and intercept of 20 Hz (R²=0.82), indicating that after the period of inhibition, the firing rate increases by 20 Hz. Data from [45], reproduced with permission