Properties of the inward-rectifying Cl- channel in rat choroid plexus: regulation by intracellular messengers and inhibition by divalent cations

The properties of the inward-rectifying Cl- conductance in rat choroid plex us epithelial cells were investigated to allow comparisons to be made with ClC-2. All experiments were performed using the whole-cell configuration of the patch-clamp method. The conductance was transiently activated using an electrode solution which contained 375 nM catalytic subunit of protein kin ase A (PKA). PKA failed to activate the conductance, however, when cells we re pre-incubated with phorbol esters, which activate protein kinase C [1 mu M phorbol 12-myristate 13-acetate (PMA) and 1 muM phorbol 12,13-dibutyrate (PDBu)]. Sustained activation of the conductance by PKA was observed in Ca2 +-free conditions (5 mM BAPTA in the electrode solution), or when 100 nM ca lphostin C, a PKC inhibitor, was added to the electrode solution. The inwar d-rectifying Cl- conductance in choroid plexus is therefore similar to ClC- 2 in that it is inhibited by PKC. The inward-rectifying conductance was blo cked when Cd2+ (30 and 300 muM) and Zn2+ (1, 30 and 300 muM) were added to, the bath solution. ClC-2 channels are also blocked by Zn2+ and Cd'S. The m agnitude of the inward conductance was dependent on the concentration of AT P in the electrode solution. The conductance was not observed when ATP in t he electrode was replaced with non-hydrolysable ATP analogues {adenosine 5' -O-(3-thiotriphosphate) (ATP[gamma -S]) and 5'-adenylylimidodiphosphate (AM P-PNP)}, but it was supported by UTP and GTP. These data contrast with thos e of previous studies in which ClC-2, channels were activated in the absenc e of ATP. In conclusion, the inward-rectifying Cl- channel in rat choroid p lexus shares some properties with ClC-2 (inhibition by PKC and block by div alent cations), but differs in that it depends on intracellular ATP.