Developmentally regulated expression of the calcium-dependent potassium channel and calcium channels during maturation of the rat cerebellum

Potassium channels govern the duration and frequency of excitable membrane events, and thus may regulate voltage-dependent signals that are important in neuronal development. This study assesses the developmental expression of two classes of K⁺ channels in vivo and in vitro in the rat cerebellum. In vivo, the level of mslo-related transcript for the Ca²⁺-dependent K⁺ channel (KCa) was shown by Northern analysis to be upregulated during development, whereas transcripts for delayed rectifier (KD) channels remained fairly constant. The same pattern of in vivo development was demonstrated with functional assays by expression in Xenopus oocytes of poly A-enriched RNA isolated from postnatal rat cerebella. In vitro, single channel studies of Purkinje neurons showed that KCa channel activity was increased during development and KD channel activity remained stable. Although the semi-quantitative Reverse Transcription-Polymerase Chain Reaction (RT-PCR) showed that the level of transcripts of the KCa channel sequence remained constant in control culture, the developmental pattern that was seen in vivo was mimicked in vitro when cultures were treated chronically with tetraethylammonium (TEA, 1mM). Chronic treatment with 10 mM extracellular KCl resulted in an upregulation of KCa transcripts similar to that seen with chronic TEA. The stimulatory effects of TEA or KCl were negated in low external calcium (0.1 mM), suggesting that KCa transcript levels were influenced by depolarization and calcium entry. The KCa channels may in part contribute to the mature electrical properties of Purkinje neurons. This was supported by evidence that developmental trends in cellular firing activity were antagonized by decreased KCa channel abundance caused by chronic treatment with TEA. Voltage-gated Ca²⁺ channels (N, R and P type) were developmentally down-regulated at the transcriptional level in control cultures. Chronic treatment with TEA increased the transcript levels for N and R type Ca²⁺ channels, but not for P type, suggesting that the various types of Ca²⁺ channels were differentially regulated. Ca²⁺ signaling plays a key role in neuronal development in many cells. The KCa and Ca²⁺ channels regulate Ca²⁺-entry, and may thus influence the neuronal differentiation