Differential expression of the human chloride channel genes in the trabecular meshwork under stress conditions

Among other channels, voltage-gated chloride channels (CIC) regulate cell volume, membrane potential and cellular transport. Because changes in trabecular meshwork (TM) cell volume influence Outflow facility and because the relative abundance of a gene's transcript is all indication of the relevance of the gene's function, we investigated the presence and relative expression of seven members of the CLCN gene family in the human TM. To elucidate the role of CIC-2 and CIC-3 in cell swelling, we studied changes in their mRNA levels after hypotonic shock. In addition, to examine the potential involvement of these two channels in conditions associated with glaucoma, we determined their transcripts levels in response to elevated intraocular pressure (IOP) and dexamethasone (DEX). For our evaluations, we used nontransformed human TM cells and perfused human anterior segments from post-mortern donors. For hypotonic shock, cells were exposed to 260 m0sm kg(-1) medium for 15 and 30 min. For DEX, cells were treated with 0.1 mu m DEX for 1, 4 and 10 days. For elevated IOP, one eye of each pair of perfused human anterior segments was subjected to Delta P 38 +/- 4 mmHg for 1 hr, 4 and 7 days while the contralateral remained at baseline pressure as a control. CICs transcripts were determined by relative quantitative RT-PCR. Our results showed that all transcripts but CIC-1 were detected in HTM cells. CIC-2 and CIC-3 were the most abundant and comprised about twice the amount of CIC-6 and CIC-7 and four times that of CIC-4 and CIC-5. Hypotonic conditions consistently up regulated CLCN2 and slightly up regulated CLCN3. After short periods of elevated pressure. CIC-2 and CIC-3 transcripts were increased but CIC-2 induction was significantly higher than that of CIC-3. In contrast, after long pressure insults (7 days), CIC-3 mRNA was significantly increased while CLCN2 was not changed. DEX treatment markedly down regulated CLCN3 and little, if any, reduced CIC-2. The extent of response of the CLCN2 and CLCN3 to these conditions was markedly affected by individual traits but at all times maintained the relative expression pattern of both genes. CLCN2 gene expression was predominantly influenced by cell volume regulation while that of CLCN3 was preferentially affected by conditions associated with TM pathology. (c) 2005 Elsevier Ltd. All rights reserved.