Effects on dendritically located H‐current on synaptic integration: a mathematical model

Abstract

The h‐current (Ih) is a cation current that improves cell excitability in three interrelated ways: it helps to determine the resting potential and firing frequency; it reduces the amplitude and duration of hyperpolarizing inputs; and it generates rhythmic cell activity when coupled to other voltage dependent currents. However, the role of Ih in the excitability of nerve cells may deviate from the functions just mentioned. Dendritically located h‐channels, for example, may obstruct synaptic integration and thus reduced cell excitability. In this work we use a simple mathematical model to study how synaptic integration is affected by the presence of Ih in the dendrite of a neuron that consists of two compartments: the soma and one dendrite. The mathematical model simulates the effect of the activation of a synaptic conductance on the firing rate. Model simulations were conducted for a base case (none of the compartments contain Ih) and two cases where Ih was placed at the soma or at the dendrite but not in both compartments. The simulation results clearly show that the effect of Ih on cell firing rate is dependent on its location in the cell membrane. In particular, dendritically located Ih decreases cell firing rate. Therefore, a negative shift of the voltage dependence of dendritically located Ih may increase cell excitability whereas a positive shift may decrease it. This is consistent with experimental data.