L-type calcium channels mediate calcium ocillations in early postnatal Purkinje neurons

Abstract

Ca2+ signaling is important in many fundamental neuronal processes including neurotransmission, synaptic plasticity, neuronal development, and gene expression. In cerebellar Purkinje neurons, Ca2+ signaling has been studied primarily in the dendritic region where increases in local Ca2+ have been shown to occur with both synaptic events and spontaneous electrical activity involving P-type voltage-gated Ca2+ channels (VGCCs), the predominant VGCC expressed by Purkinje neurons. Here we show that Ca2+ signaling is also a prominent feature of immature Purkinje neurons at developmental stages that precede expression of dendritic structure and involves L-type rather than P-type VGCCs. Immature Purkinje neurons acutely dissociated from postnatal day 4-7 rat pups exhibit spontaneous cytoplasmic Ca2+ oscillations. The Ca2+ oscillations require entry of extra-cellular Ca2+, are blocked by tetrodotoxin, are communicated to the nucleus, and correlate closely with patterns of endogenously generated spontaneous and evoked electrical activity recorded in the neurons. Immunocytochemistry showed that L-, N-, and P/Q-types of VGCCs are present on the somata of the Purkinje neurons at this age. However, only the L-type VGCC antagonist nimodipine effectively antagonized the Ca2+ oscillations; inhibitors of P/Q and N-type VGCCs were relatively ineffective. Release of Ca2+ from intraceliular Ca2+ stores significantly amplified the Ca2+ signals of external origin· These results show that a somatic signaling pathway that generates intracellular Ca2+ oscillations and involves L-type VGCCs and intracellular Ca2+ stores plays a prominent role in the Ca2+ dynamics of early developing Purkinje neurons and may play an important role in communicating developmental cues to the nucleus.