[29] High-level expression and detection of ion channels in Xenopus oocytes

Because the initial demonstration by Miledi and co-workers that ion channels and neural receptors can be functionally expressed in Xenopus oocytes, this system has become a standard for demonstrating that a specific cloned cDNA encodes a functional channel or receptor. Many different ion channels and receptors have been expressed in oocytes for functional analysis, and oocytes have been used for functional cloning of receptors, as described by Ltibbert et al. and Julius et al. RNA for injection into oocytes can be isolated from the appropriate tissue sample or cell line, or it can be synthesized in vitro from a cDNA clone. This chapter discusses some of the approaches that are used for high-level expression and analysis of cloned ion channels in Xenopus oocytes. This expression system has the advantage that channels can be expressed and analyzed by electrophysiologic, biochemical, and physical approaches. Most of the electrophysiologic recording techniques described here on electrophysiology can be used for analysis of ion channels in oocytes. In addition, the system can be used effectively as an assay for the functional cloning of channels that have only been identified by their electrophysiologic properties. Expression of ion channels in oocytes is an excellent system for correlating structure with function using a combination of molecular biological, biochemical, and electrophysiologic techniques.