Figure 4.

Rapid and Complete Na⁺ Channel Inactivation during APs Promotes Energy Efficiency in PV⁺-BC Axons

(A) Top: Na⁺ currents evoked by an AP waveform (left) or a test pulse to 0 mV from a membrane potential of −120 mV (right) in an axonal outside-out patch (158 μm from the soma). Bottom: a test pulse to 0 mV was applied at the peak (left) or 250 μs after the peak (right) of the AP to determine the degree of Na⁺ channel inactivation. All traces are from the same experiment.

(B) Summary graph showing the amplitude of Na⁺ currents evoked by the test pulse applied at the peak or 250 μs after the peak of the AP waveform and that of the Na⁺ current elicited by applying the test pulse from −120 mV. ^∗p = 0.04.

(C) Summary graph showing the degree of Na⁺ channel inactivation at the peak and 250 μs after the AP peak. Na⁺ channel inactivation was quantified as the ratio (I/I_-120mV) of current amplitudes evoked by the test pulse applied at or after the AP peak to the maximal amplitude of the Na⁺ current elicited by the test pulse applied from a membrane potential of −120 mV. Data from the same experiment were connected by lines. Box charts indicate the median value and distribution of all data points. ^∗p = 0.04.

(D) Na⁺ currents elicited by AP waveforms of different half-durations in an axonal outside-out patch. To systematically scale the half-duration of the AP waveform, we replaced the repolarization phase of the AP waveform with linear functions of different slope values. Each AP waveform and its corresponding Na⁺ current trace were plotted in the same color.

(E) Summary graph showing the effects of changing AP half-duration on Na⁺ entry ratio in 7 axonal recordings. Data from the same experiment were connected by lines. NS indicates p = 0.4.

Whiskers in box charts indicate the 5^th and 95^th percentile of data points, and the box itself indicates median, first quartile, and third quartile of the data points.