Antisense to MDR1 mRNA reduces P-glycoprotein expression, swelling-activated Cl- current and volume regulation in bovine ciliary epithelial cells

1. Native ciliary epithelial cells from the ciliary epithelium of the eye exhibit anti-P-glycoprotein (P-gp) immunofluorescence. 2. We have used an antisense 'knock-down' approach to investigate the relationship between P-gp and the volume-activated chloride current (I-Cl,I-swell) and its role in volume regulation. 3. An antisense oligonucleotide to the human multidrug resistance (MDR1) gene, taken up bg: the cells in a dose-dependent manner, reduced P-gp immunofluorescence, inhibited I-Cl,I-swell and significantly increased the latency of activation of I-Cl,I-swell. 4. Increasing the hypotonic stress did not result in an increased activation of I-Cl,I-swell. MDR1 antisense 'knock-down' also reduced the ability of the cells to volume regulate following a hypotonic challenge. 5, These cells are known to express at least two volume-activated chloride channels, and the data suggest that P-gp is involved in the activation pathway of a subset of channels that contribute to whole-cell I-Cl,I-swell and participate in volume regulation.