Hyposmotically activated chloride channels in cultured rabbit non‐pigmented ciliary epithelial cells

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Abstract
1. We used whole-cell patch-clamp recording techniques and noise analysis of whole-cell current to investigate the properties of hyposmotic shock (HOS)-activated Cl- channels in SV40-transformed rabbit non-pigmented ciliary epithelial (NPCE) cells. 2. Under conditions designed to isolate Cl- currents, exposure of cells to hyposmotic external solution reversibly increased the whole-cell conductance. 3. The whole-cell current activated with a slow time course (> 15 min), exhibited outward rectification and was Cl- selective. 4. The disulphonic stilbene derivatives 4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS, 0.5 mM), 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS, 0. 5 mM) and 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS, 0.5 mM) produced a voltage-sensitive block of HOS-activated Cl- current at depolarized potentials, whereas niflumic acid produced a voltage-independent block of the current. 5. Under Ca2+-free conditions, HOS stimulation still reversibly activated the Cl- current, but the amplitude of current was reduced and the time course of current activation was slower compared with control (P < 0. 05). 6. The non-specific kinase inhibitor H-7 (100 microM), upregulated HOS-activated Cl- current amplitude in all cells tested (P < 0.05). 7. Noise analysis of whole-cell Cl- current indicated that cell swelling activated a high density of small conductance Cl- channels (< 1 pS). 8. We conclude that HOS primarily activates a high density of volume-sensitive small conductance Cl- channels in rabbit NPCE cells, and that Ca2+ and phosphorylation are involved in channel regulation.

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