Abstract
Chloride channels have significant functions in glial astrocytes. However, only GABAA receptor, glycine receptor and ClC-2 chloride channels have been identified in astrocytes. Thus, we here examined the expression of the ClC-1 chloride channel in rat astrocytic glioma C6 cells and rat astrocytes in primary culture. In C6 cells, five isoforms of rat ClC-1, but not rat skeletal muscle ClC-1 (SM ClC-1), were detected at the mRNA expression level. Comparison with SM ClC-1 showed that these isoforms share a short 3' end with a deletion of the nucleotides from 3115 to 3197 and a substitution of T by C at nucleotides 480 and 1733 as common features. Three of the five isoforms, M1, M2 and M3, were produced by deletion of ClC-1 exon 7, insertion of ClC-1 exon 7a and insertion of a trinucleotide, TAG, at nucleotide 858, respectively. Another isoform, M4, was produced by deletion of ClC-1 exon 8 at nucleotide 937, and the other, M5, was the same as SM ClC-1 except for the short 3' end and substitutions at the two positions. In Xenopus oocytes, only the M5 isoform could be expressed as a functional anion-selective channel. This glial ClC-1 isoform showed less dependence on voltage and extracellular Cl− than SM ClC-1, whereas the anion selectivity sequence and the pharmacological sensitivity of the glial isoform were the same as those of SM ClC-1. In rat astrocytes, two additional distinct isoforms were found to be expressed in addition to the M2 isoform. [Jpn J Physiol 54 Suppl:S68 (2004)]
