H. Kajita et al., Properties of the inward-rectifying Cl- channel in rat choroid plexus: regulation by intracellular messengers and inhibition by divalent cations, PFLUG ARCH, 440(6), 2000, pp. 933-940
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.