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

PURPOSE 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. METHODS 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. RESULTS 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. CONCLUSIONS 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.