A LARGE-CONDUCTANCE CHLORIDE CHANNEL IN PIGMENTED CILIARY EPITHELIAL-CELLS ACTIVATED BY GTP-GAMMA-S

A large-conductance (or maxi-) chloride channel was identified in bovi ne pigmented ciliary epithelial (PCE) cells using inside-out excised p atch clamp recording. The channel had a mean conductance of 293 pS whe n excised patches were bathed in symmetrical 130 mM NaCl although the conductance decreased to 209 pS when the solution bathing the cytoplas mic face of the patch contained only 33 mM NaCl. The channel was highl y selective for chloride, with a P-Cl/P-Na = 24. A flickery, reversibl e block was produced by the diuretic stilbene 4-acetamido-4'-isothiocy anatostilbene-2,2'- disulfonic acid (SITS), while 4,4'-diisothiocyanat ostilbene-2,2'-disulfonic acid (DIDS) produced a permanent block. The channel was rarely active in cell-attached patches and usually require d several minutes of polarization before activity could be detected in excised patches, a process known as metagenesis. Once activated, the channel was voltage-dependent and was mainly open within the voltage r ange -30 to +30 mV closing when the membrane was polarized to larger v alues. GTP gamma S (100 mu M) activated the channel with a latency of 170 sec when applied to the cytoplasmic face of patches. This activati on was not reversible upon return to control solution within the durat ion of the experiment. We assess the available evidence and suggest a role for this channel in volume regulation.