Chronic pharmacological blockade of the Na+/Ca2+ exchanger modulates the growth and development of the Purkinje cell dendritic arbor in mouse cerebellar slice cultures

The Na+/Ca2+ exchanger (NCX) is a bidirectional plasma membrane antiporter involved in Ca2+ homeostasis in eukaryotes. NCX has three isoforms, NCX1–3, and all of them are expressed in the cerebellum. Immunostaining on cerebellar slice cultures indicates that NCX is widely expressed in the cerebellum, including expression in Purkinje cells. The pharmacological blockade of the forward mode of NCX (Ca2+ efflux mode) by bepridil moderately inhibited growth and development of Purkinje cell dendritic arbor in cerebellar slice cultures. However, the blockade of the reverse mode (Ca2+ influx mode) by KB‐R7943 severely reduced the dendritic arbor and induced a morphological change with thickened distal dendrites. The effect of KB‐R7943 on dendritic growth was unrelated to the activity of voltage‐gated calcium channels and was also apparent in the absence of bioelectrical activity indicating that it was mediated by NCX expressed in Purkinje cells. We have used additional NCX inhibitors including CB‐DMB, ORM‐10103, SEA0400, YM‐244769, and SN‐6 which have higher specificity for NCX isoforms and target either the forward, reverse, or both modes. These inhibitors caused a strong dendritic reduction similar to that seen with KB‐R7943, but did not elicit thickening of distal dendrites. Our findings indicate that disturbance of the NCX‐dependent calcium transport in Purkinje cells induces a reduction of dendritic arbor, which is presumably caused by changes in the calcium handling, and underline the importance of the calcium equilibrium for the dendritic development in cerebellar Purkinje cells. The blockade of the forward or reverse mode of the Na+/Ca2+ exchanger in cerebellar slice cultures leads to a reduction of the Purkinje cell dendritic arbor size. KB‐R7943‐treated cultures showed thickened distal dendrites, while other NCX inhibitors reduced dendritic arbor size without affecting dendritic morphology. Our findings show the importance of NCX‐dependent calcium transport in Purkinje cells for dendritic development.