Chloride channel blockers activate an endogenous cationic current in oocytes of Bufo arenarum

A two-electrode, voltage-clamp technique was used to measure the effect of the Cl- channel blockers, 9-anthracene carboxylic acid and niflumic acid, upon the ionic currents of oocytes of the South American toad Bufo arenarum. The main results were: (1) both blockers produced a reversible increase of the outward currents on a dose-dependent manner; (2) the activated outward current was voltage dependent; (3) the 9-anthracene carboxylic acid-sensitive current was blocked with barium; and (4) the effect of 9-anthracene carboxylic acid was more pronounced in a zero-K+ solution than in standard (2 mmol 1(-1)) or high (20 mmol 1(-1)) K+ solutions, indicating that a K+ conductance is activated. The effect of the Cl- channel blockers could be due to a direct interaction with endogenous cationic channels. Another possible explanation is that Cl- that enter the cell during depolarizing steps in control solution inhibit this cationic conductance; thus, the blockade of Clchannels by 9-anthracene carboxylic acid and niflumic acid would remove this inhibition, allowing the cationic current to flow freely.