Swelling-activated potassium channel in porcine pigmented ciliary epithelial cells.

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Ion channels in the ciliary epithelium play critical roles in the formation of aqueous humor in the eye. The present study identified a novel, swelling-activated K(+) current in freshly dissociated porcine pigmented ciliary epithelial cells. Ciliary epithelial cells were freshly dissociated from porcine eyes. Whole-cell currents were recorded by the patch-clamp technique in pigmented and nonpigmented ciliary epithelial cell (PCE-NPCE) pairs or single PCE cells. The 0-current potential was -49 ± 13 mV in PCE-NPCE cell pairs (n = 97) and -52 ± 12 mV in single PCE cells (n = 30). Whole-cell currents in these cells were dominated by an outwardly rectifying K(+) current activated by potentials more positive than -90 mV, which never inactivated during prolonged depolarization. The K(+) current was significantly augmented by hypotonic cell perfusion. External Ba(2+) was a blocker of this K(+) conductance (IC(50) of 0.38 mM), but the conductance was insensitive to external TEA(+). Linopirdine, a specific inhibitor of KCNQ channels, effectively blocked the K(+) current in these PCE cells. Porcine PCE cells express a swelling-activated K(+) channel, which may be a member of the KCNQ/Kv7 channel family. This K(+) channel is active near resting potentials and could contribute to the regulation of cell volume and water transport via the ciliary epithelia.