The temporal dynamics of membrane voltage changes in neurons is controlled by ionic currents. These currents are characterized by two main properties: conductance and kinetics. The hyperpolarization-activated current ( Ih ) strongly modulates subthreshold potential changes by shortening the excitatory postsynaptic potentials and decreasing their temporal summation. Whereas the shortening of the synaptic potentials caused by the Ih conductance is well understood, the role of the Ih kinetics remains unclear. Here, we use a model of the Ih current model with either fast or slow kinetics to determine its influence on the membrane time constant (\tau_m) of a CA1 pyramidal cell model. Our simulation results show that the Ih with fast kinetics decreases \tau_m and attenuates and shortens the excitatory postsynaptic potentials more than the slow Ih . We conclude that the Ih activation kinetics is able to modulate \tau_m and the temporal properties of excitatory postsynaptic potentials (EPSPs) in CA1 pyramidal cells. In order to elucidate the mechanisms by which Ih kinetics controls \tau_m, we propose a new concept called "time scaling factor". Our main finding is that the Ih kinetics influences \tau_m by modulating the contribution of the Ih derivative conductance to \tau_m.
The temporal dynamics of membrane voltage changes in neurons is controlled by ionic currents. These currents are characterized by two main properties: conductance and kinetics. The hyperpolarization-activated current ( I_{\rm h ) strongly modulates subthreshold potential changes by shortening the excitatory postsynaptic potentials and decreasing their temporal summation. Whereas the shortening of the synaptic potentials caused by the I_{\rm h conductance is well understood, the role of the I_{\rm h kinetics remains unclear. Here, we use a model of the I_{\rm h current model with either fast or slow kinetics to determine its influence on the membrane time constant (\tau_m) of a CA1 pyramidal cell model. Our simulation results show that the I_{\rm h with fast kinetics decreases \tau_m and attenuates and shortens the excitatory postsynaptic potentials more than the slow I_{\rm h . We conclude that the I_{\rm h activation kinetics is able to modulate \tau_m and the temporal properties of excitatory postsynaptic potentials (EPSPs) in CA1 pyramidal cells. In order to elucidate the mechanisms by which I_{\rm h kinetics controls \tau_m, we propose a new concept called "time scaling factor". Our main finding is that the I_{\rm h kinetics influences \tau_m by modulating the contribution of the I_{\rm h derivative conductance to \tau_m.
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