Diversity of potassium channels in neuronal dendrites

Complex computations in the nervous system begin with electrical signals generated in single neurons. Such signals include action potentials mediated by the opening of voltage-dependent ion channels, and synaptic potentials arising from neurotransmitter receptor activation. The amplitude, waveform, and propagation of action potentials and synaptic potentials influence cellular signaling in profound ways, and are largely determined by activities of ion channels in the cell membrane. The location and properties of ion channels therefore play critical roles in shaping electrical signaling in the neuron, which is the foundation for more complex computations at network levels. This review summarizes what we know about the great diversity of K(+) channels found in neuronal dendrites, the subcellular compartment where synaptic signals integrate and where various forms of plasticity occur. Specifically, we discuss the molecular identity, the distribution, kinase modulation, biophysical properties, and functional roles of a variety of K(+) channels including voltage-gated, calcium-activated, and ligand-gated/G-protein coupled K(+) channels. One emerging theme from recent literature is the recognition that K(+) channels are powerful regulators of the function of dendrites. A second theme indicates that this K(+) channel regulation depends on their unique subcellular distribution. In particular, the mechanisms underlying the establishment and maintenance of non-uniform distributions of ion channels are beginning to be understood in greater detail. An especially intriguing aspect of above mechanisms is that they are achieved through protein kinase phosphorylation and may thus be activity-dependent. In parts of this review, we choose to focus on CA1 pyramidal neurons of the rodent hippocampus and the K(+) channels in their dendrites. Being one of the best-characterized cell types in the nervous system, the CA1 pyramidal neuron has long been studied as a prototypic neuron from which general rules of neuronal computation and synaptic plasticity emerge. A great deal of what we know about dendritic K(+) channels comes from studies on CA1 pyramidal neurons. Where available, we also include up-to-date findings on dendritic K(+) channels in other cell types.