Impact of Fast Sodium Channel Inactivation on Spike Threshold Dynamics and Synaptic Integration
A, Distribution of half-inactivation voltage (Vi) of Na channels expressed in exogenous systems (from a database of 40 Na channels reported in Angelino and Brenner, 2007 ), including central neuron channel types (red), sensory neuron channel types (blue) and muscular channel types (green). Assuming a minimum spike threshold between −55 mV and −45 mV (dashed lines), channels on the left have variable threshold while channels of the right have a constant threshold. B, Inactivation (ki) vs. activation slope (ka) for the same dataset. Channels with Vi<−50 mV (variable threshold) are indicated by a black contour. These channels have high threshold variability when ka>ki (right of the dashed line). C, Distribution of Vi for Na channels expressed in central neurons in situ (see Table S1). The threshold should be variable in most cases. D, Inactivation (ki) vs. activation slope (ka) for the same dataset. High threshold variability is predicted in about half cases.