Persistent sodium is a better linearizing mechanism than the hyperpolarization-activated current

The hyperpolarization-activated mixed cation and the persistent sodium conductances are compared as linearizing mechanisms for somatodendritic synaptic integration in steady-state systems. In the steady-state model used, the persistent sodium conductance creates a well-defined region of linear synaptic excitation, from -66 to -55mV. This corresponds to a moderate level of synaptic depolarization (total active synaptic conductance ranging from 2 to 5.9 nS). In contrast, a model enhanced with a hyperpolarization-activated mixed cation conductance only linearizes over a short voltage range, from -68 to -61mV. This in turns corresponds to very low levels of synaptic activity (0-3.7 nS). Given in vivo recordings of firing thresholds for nonbursting neurons ranging from around -60 to -55mV, the persistent sodium current emerges as the better linearizing mechanism for these neurons because it operates across the full physiologically relevant voltage range for perisomatic, proximal dendritic synaptic excitation.