Characterization of a novel voltage-dependent outwardly rectifying anion current in Caenorhabditis elegans oocytes

An inwardly rectifying swelling- and meiotic cell cycle-regulated anion current carried by the ClC channel splice variant CLH-3b dominates the whole cell conductance of the Caenorhabditis elegans oocyte. Oocytes also express a novel outwardly rectifying anion current termed I(Cl,OR). We recently identified a worm strain carrying a null allele of the clh-3 gene and utilized oocytes from these animals to characterize I(Cl,OR) biophysical properties. The I(Cl,OR) channel is strongly voltage dependent. Outward rectification is due to voltage-dependent current activation at depolarized voltages and rapid inactivation at voltages more hyperpolarized than approximately +20 mV. Apparent channel open probability is zero at voltages less than +20 mV. The channel has a 4:1 selectivity for Cl(-) over Na(+) and an anion selectivity sequence of SCN(-) > I(-) > Br(-) > Cl(-) > F(-). I(Cl,OR) is relatively insensitive to most conventional anion channel inhibitors including DIDS, 4,4'-dinitrostilbene-2,2'-disulfonic acid, 9-anthracenecarboxylic acid, and 5-nitro-2-(3-phenylpropylamino)benzoic acid. However, the current is rapidly inhibited by niflumic acid, metal cations including Gd(3+), Cd(2+), and Zn(2+), and bath acidification. The combined biophysical properties of I(Cl,OR) are distinct from those of other anion currents that have been described. During oocyte meiotic maturation, I(Cl,OR) activity is rapidly downregulated, suggesting that the channel may play a role in oocyte Cl(-) homeostasis, development, cell cycle control, and/or ovulation.