Model organisms: New insights into ion channel and transporter function. Caenorhabditis elegans ClC-type chloride channels: novel variants and functional expression

Six ClC-type chloride channel genes have been identified in Caenorhabditis elegans, termed clh-1 through clh-6. cDNA sequences from these genes sugges t that clh-2, clh-3, and clh-4 may code for multiple channel variants, brin ging the total to at least nine channel types in this nematode. Promoter-dr iven green fluorescent protein (GFP) expression in transgenic animals indic ates that the protein CLH-5 is expressed ubiquitously, CLH-6 is expressed m ainly in nonneuronal cells, and the remaining isoforms vary from those rest ricted to a single cell to those expressed in over a dozen cells of the nem atode. In an Sf9 cell expression system, recombinant CLH-2b, CLH-4b, and CL H-5 did not form functional plasma membrane channels. In contrast, both CLH -1 and CLH-3b produced strong, inward-rectifying chloride currents similar to those arising from mammalian ClC2, but which operate over different volt age ranges. Our demonstration of multiple CLH protein variants and comparis on of expression patterns among the clh gene family provides a framework, i n combination with the electrical properties of the recombinant channels, t o further examine the physiology and cell-specific role each isoform plays in this simple model system.