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 l(-1)) or high (20 mmol l(-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 Cl(-) channels by 9-anthracene carboxylic acid and niflumic acid would remove this inhibition, allowing the cationic current to flow freely.
Cavarra
M S
MS
Facultad de Medicina (UBA), Instituto de Investigaciones Médicas Alfredo Lanari, C. de Malvinas 3150, 1427 Buenos Aires, Argentina.
del Mónaco
S M
SM
Kotsias
B A
BA
D000818:Animals; D000873:Anthracenes / Q000737:chemistry / Q000494:pharmacology*; D001464:Barium / Q000494:pharmacology; D002022:Bufo arenarum / Q000502:physiology*; D018118:Chloride Channels / Q000037:antagonists & inhibitors*; D002712:Chlorides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D018698:Glutamic Acid / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D009544:Niflumic Acid / Q000737:chemistry / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D011188:Potassium / Q000494:pharmacology
D000873:Anthracenes; D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D001464:Barium; D018698:Glutamic Acid; D009544:Niflumic Acid; C010030:9-anthroic acid; D011188:Potassium