INHIBITION OF THE INWARD-RECTIFYING CL- CHANNEL IN RAT CHOROID-PLEXUSBY A DECREASE IN EXTRACELLULAR PH

1. The sensitivity of the inward-rectifying Cl- channel in choroid ple xus to changes in external pH (pH(o)) was examined. 2. Cl- currents we re recorded using whole-cell patch-clamp methods. The inward-rectifyin g channel was activated by 375 nM of the catalytic subunit of protein kinase A which was added to the electrode solution. 3. Reducing pH(o) from 7.3 to 6.5 inhibited the inward-rectifying Cl- currents, whereas an increase in current was observed when pH(o) was elevated to 8.5. Th e inhibition of the conductance exhibited a sigmoidal relationship wit h decreasing pH over a range of 8.5 to 5.5. A half-maximal inhibition of the current was observed at pH 7.3. 4. The inhibition of the whole- cell current by reducing pH(o) suggests that it is carried by channels which are distinct from other inward-rectifier Cl- channels, e.g. ClC -2, phospholemman and the channel in Xenopus oocytes.