Distribution of slow AHP channels on hippocampal CA1 pyramidal neurons

This work was designed to localize the Ca²⁺-activated K⁺ channels underlying the slow afterhyperpolarization (sAHP) in hippocampal CA1 pyramidal cells. Cell-attached patches on the proximal 100 μm of the apical dendrite contained K⁺ channels, but not sAHP channels, activated by backpropagating action potentials. Amputation of the apical dendrite ~30 μm from the soma, while simultaneously recording the sAHP whole cell current at the soma, depressed the sAHP amplitude by only ~30% compared with control. Somatic cell-attached and nucleated patches did not contain sAHP current. Amputation of the axon ≥20 μm from the soma had little effect on the amplitude of the sAHP recorded in cortical pyramidal cells. By this process of elimination, it is suggested that sAHP channels may be concentrated in the basal dendrites of CA1 pyramids.