Dendritic potassium channels in hippocampal pyramidal neurons

Potassium channels located in tart! dendrites of hippocampal CA1 pyramidal neurons control the shape and amplitude of back-propagating action potentials, the amplitude of excitatory postsynaptic potentials and dendritic excitability. Non-uniform gradients in the distribution of potassium channels in the dendrites make the dendritic electrical properties markedly different from those found in the soma. For example, the influence of a fast, calcium dependent potassium current on action potential repolarization is progressively reduced in the first 150 mu m of the apical dendrites, so that action potentials recorded farther than 200 mu m from the soma have no fast after-hyperpolarization and are wider than those in the soma. The peak amplitude of back-propagating action potentials is also progressively reduced in the dendrites because of the increasing density of a transient potassium channel with distance from the soma. The activation of this channel can be reduced by the activity of a number of protein kinases as well as by prior depolarization. The depolarization from excitatory postsynaptic potentials (EPSPs) can inactivate these A-type K+ channels and thus lead to an increase in the amplitude of dendritic action potentials, provided the EPSP and the action potentials occur within the appropriate time window: This time window could be in the order of 15 ms and may play a role in long-term potentiation induced by pairing EPSPs and back-propagating action potentials.