High-Throughput Screening of Neuronal Cl- Channels: Why and How?

Much remains to be learned about the structures, functions and therapeutic potentials of anion-permeable ion channels expressed throughout the nervous system. For example, the molecular identities of Ca2+- and swelling-activated Cl- channels are still unknown. Even in well-established neuronal anion channel families (the CLC and GABA type-A ion channel receptors), significant gaps exist in our understanding of the physiological functions and sub-cellular distributions of particular subtypes. The first part of this review summarises the current status of this field and discusses how the discovery of highly-selective pharmacological probes will advance our understanding of the molecular identities, cellular and sub-cellular distributions and functional roles of neuronal Cl- channels. Where relevant, the therapeutic potential of these channels is also discussed. The review then considers the relative merits of high-throughput methods that have been employed to screen anion-permeable channels. It concludes that several methods are potentially suited to screening homogeneous assays (such as stably-expressing cell lines), with the choice of method being governed largely by the detection equipment available. However, an anion-quenchable yellow fluorescent protein method is unique in that it retains full dynamic range in assays comprising transiently-transfected cells where the percentage of cells expressing recombinant channels is significantly < 100%. This feature is a significant advantage for screening the vast range of possible GABA type-A receptor subunit combinations where the creation of numerous stably-expressing cell lines would otherwise pose a substantial logistical challenge.