REGULATORY MECHANISMS FOR THE DENSITY AND PROPERTY OF K^+CHANNELS

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Channel density is a fundamental factor determining neuronal firing, and is primarily regulated during development through transcriptional and translational regulation. In adult rats, striatal cholinergic interneurons have a prominent A-type current and co-express Kv4.1 and Kv4.2 mRNAs. The contribution of Kv4.2 and Kv4.1 to the A-type current in cholinergic interneurons during development, however, is not known. Using patch-clamp recording and semi-quantitative single-cell RT-PCR techniques, we have examined the postnatal development of A-type current and the expression of Kv4.2 and Kv4.1, in rat striatal cholinergic interneurons. A-type current was detectable at birth and its amplitude was up-regulated with age, reaching a plateau at about three weeks after birth. Kv4.2 mRNA was detectable at birth and the expression level increased exponentially with age, reaching a plateau by three weeks postnatal. In contrast, Kv4.1 mRNA was not detectable during the first week after birth, and the expression level did not show a clear tendency with age. Taken together, our results suggest that Kv4.2 plays an essential role in producing the A-type current in striatal cholinergic interneurons during the entire course of postnatal development.