Low-threshold potassium channels and a low-threshold calcium channel regulate Ca 2+ spike firing in the dendrites of cerebellar Purkinje neurons: a modeling study

Abstract

Various types of voltage-gated ion channels are distributed along the dendrites of neurons in the central nervous system. We have recently shown experimentally that the dendrites of cerebellar Purkinje neurons contain low-threshold voltage-gated Ca 2+ channels and low-threshold voltage-gated K + channels. Although we found that these channels are involved in regulating the onset of Ca 2+-dependent action potentials in the dendrites, we were unable to identify which of the known types of low-threshold Ca 2+ channels and K + channels were responsible, since there was no reliable method of discriminating between them. Here, we have built a detailed compartmental model of a Purkinje neuron by incorporating two types of low-threshold Ca 2+ channel (T-type and class-E, or R-type) and two types of low-threshold K + channel (A-type and D-type), in addition to another eight voltage-gated channel types, using a compartmental model neuron simulator. The model reproduces the basic features of the depolarization-induced responses of Purkinje neurons, such as fast Na + spikes in the soma, Ca 2+ spikes in the dendrites, the slow onset of Ca 2+ spikes, repetitive Ca 2+ spikes in the presence of TTX, the marked shortening of Ca 2+ spike onset in the presence of 4-aminopydridine, and the longer Ca 2+ spike onset in the presence of Ni 2+. Our model shows that the D-type K + channel and the class-E Ca 2+ channel regulate the onset of depolarization-induced Ca 2+ spikes in Purkinje neurons. These channels might be involved in integrating synaptic inputs in Purkinje neurons.