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N. Urushisaki, M. Takahira, M. Sakurai, N. Sakurada, K. Sugiyama; Swelling–Activated K+ Channel Expressed in Porcine Ciliary Pigmented Epithelial Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):225.
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Chloride transport across the ciliary epithelium plays a critical role in aqueous humor formation. In other secretary epithelia, K+ recycling through K+ channels is crucial for the transepithelial transport of chloride, but the specific K+ channels that serve this function in the ciliary epithelium have not been elucidated. The purpose of this study was to investigate the electrophysiological and pharmacological properties of K+ channels in the pigmented ciliary epithelium (PE).
Porcine ciliary epithelial cells were freshly dissociated using papain and perfused with HEPES–buffered Ringer solution. Whole–cell currents were recorded using the perforated–patch configuration of the patch–clamp technique from pairs of PE and nonpigmented ciliary epithelial (NPE) cells, or single PE cells.
PE–NPE cell pairs had a zero–current potential averaging –48 mV (n = 79) and exhibited a prominent outward K+ current. This current activated slowly at voltages positive to approximately –90 mV (V1/2 = –63 mV, n=12) and did not inactivate during prolonged depolarization. An identical K+ current was also observed in isolated PE cells (n=11). The IC50 for current block by the classical K+ channel inhibitor tetraethylammonium (TEA) was >20 mM. Exposure to hypo–osmotic solution (210 mOsm) markedly augmented this K+ current.
Freshly dissociated porcine PE cells express an osmo–sensitive K+ channel. This channel may recycle K+ in the pigmented ciliary epithelium and thereby regulate the transepithelial transport of chloride.
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