Depolarization-induced calcium signals in the somata of cerebellar Purkinje neurons

Cerebellar Purkinje neurons express voltage-gated Ca²⁺ channels that are located on their somata and dendrites. Previous reports, based on microelectrode recordings and fura-2 Ca²⁺ imaging, suggested that depolarization-mediated intracellular Ca²⁺ signaling is confined almost completely to the dendrites. We investigated the spatial distribution of depolarization-induced Ca²⁺ signals in Purkinje neurons by applying whole-cell patch-clamp recordings combined with fluorometric Ca²⁺ imaging to cerebellar slices. Under our recording conditions, depolarizing pulses produced the dendritic but also large somatic Ca²⁺ signals. By selective perfusion of the slice with a Ca²⁺-free EGTA-containing solution, we could isolate experimentally Ca²⁺ signals in somata and dendrites, respectively. Moreover, experiments performed on cerebellar slices from young rats (up to postnatal day 6), in which Purkinje neurons are almost completely devoid of dendrites, showed that Ca²⁺ currents produced by the activation of somatic Ca²⁺ channels are associated with Ca²⁺ transients similar to those seen in the somata of adult Purkinje neurons. Our results strongly indicate that the depolarization-induced somatic Ca²⁺ signals are caused by Ca²⁺ entry through voltage-gated channels located on the somatic membrane of Purkinje neurons.