Focal activation of glutamate receptors in distal dendrites of hippocampal pyramidal cells triggers voltage-dependent Ca(2+) channel-mediated plateau potentials that are confined to the stimulated dendrite. We examined the role of dendritic K(+) conductances in determining the amplitude, duration, and spatial compartmentalization of plateau potentials. Manipulations that blocked SK-type Ca(2+)-activated K(+) channels, including apamin and BAPTA dialysis, increased the duration of plateau potentials without affecting their amplitude or compartmentalization. Manipulations that blocked Kv4.2 A-type K(+) channels, including a dominant-negative Kv4.2 construct and 4-aminopyridine, increased the amplitude of plateau potentials by allowing them to recruit neighboring dendrites. Prolongation of plateau potentials or block of Kv4.2 channels at branch points facilitated the ability of dendritic excitation to trigger fast action potentials. SK channels thus underlie repolarization of dendritic plateau potentials, whereas Kv4.2 channels confine these potentials to single dendritic branches, and both act in concert to regulate synaptic integration.