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

通道密度是决定神经元放电的一个基本因素，在发育过程中主要通过转录和翻译调节来调节。成年大鼠纹状体胆碱能中间神经元具有显著的A型电流，并共同表达Kv4.1和Kv4.2mRNAs。我们先前已经证明，Kv4.2在纹状体胆碱能中间神经元产生A-型电流中起重要作用。在半定量研究中，我们发现A-型电流和Kv4.2mRNA的发育过程可以用转录和翻译机制以及通道蛋白和mRNAs的降解来很好地描述。因此，通道密度的调节主要由转录、翻译和降解的速率决定。在这里，我们开发了一种体外制剂，用它可以使纹状体切片存活数天。在此基础上，通过加入蛋白质合成阻断剂和转录阻断剂，研究了A型通道蛋白和Kv4.2mRNA的周转率。我们从两周龄大鼠的脑片上发现，A-型电流在一天内减少到一半。然而，三周龄大鼠的电流花了两天时间才减少到一半。因此，通道蛋白的周转可能与年龄有关。Kv4.2基因的半衰期为1天。本研究建立的脑片制备方法可用于通道密度调节的进一步研究。纹状体胆碱能中间神经元也表达延迟整流电流。延迟整流的候选基因也在这项研究中进行了测试。

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. We have previously shown that Kv4.2 plays an essential role in producing the A-type current in striatal cholinergic interneurons. In a semi quantitative study, we found that the developmental time course of A-type current and Kv4.2 mRNA could be well described by a transcriptional and translation mechanism, together with degradation of channel proteins and mRNAs. The regulation of channel density is thus primarily determined by the rates of transcription, translation, and degradation. Here we have developed an in vitro preparation with which striatal slices could be kept alive for several days. Using this preparation, we studied the turnover rate of A-type channel protein and Kv4.2 mRNA by adding blockers of protein synthesis and transcription blockers. We found that A-type current was reduced to half value in one day fro slices from two weeks old rats. However, it took two days for currents in three weeks old rats to be reduced to half value. Thus the turnover of channel protein is likely to be age dependent. The half life of Kv4.2 mRNA was fund to be one day. The slice preparation developed in this study should be useful for further study on channel density regulation.Striatal cholinergic interneurons also express a delayed rectifier current. Candidate genes for the delayed rectifier have also been tested in this study.