Dendritic Ca2+-activated K+ conductances regulate electrical signal propagation in an invertebrate neuron

Abstract

Activity-dependent changes in the short-term electrical properties of neurites were investigated in the anterior pagoda (AP) cell of leech. Imaging studies revealed that backpropagating Na+ spikes and synaptically evoked EPSPs caused Ca2+ entry through low-voltage-activated Ca2+ channels that are distributed throughout the neurites. Voltage-clamp recordings from the soma revealed a TEA-sensitive outward current that was reduced when Ca2+ entry was blocked with Co2+ or when the intracellular concentration of free Ca2+ was reduced by a high-affinity Ca2- buffer. Ca2+ released in the neurite from a caged Ca2+ compound caused a hyperpolarization of the membrane potential. These data imply that the AP cell expresses Ca2+- activated K+ conductances, and that these conductances are present in the neurites. When the Ca2+activated K+ current was reduced through the block of Ca2+ entry, backpropagating Na+ spikes and synaptically evoked EPSPs increased in amplitude. Hence, the activity-dependent changes in the intracellular [Ca2+] together with the Ca2+-activated K+ conductances participate in the regulation of dendritic signal propagation.