Premium
Dual effect of blocking agents on Ca 2+ ‐activated Cl − currents in rabbit pulmonary artery smooth muscle cells
Author(s) -
Piper A. S.,
Greenwood I. A.,
Large W. A.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2001.013270
Subject(s) - dids , chemistry , niflumic acid , reversal potential , calcium , biophysics , medicinal chemistry , analytical chemistry (journal) , stereochemistry , patch clamp , biochemistry , chromatography , receptor , membrane , biology , organic chemistry
The effects of the Cl − channel antagonists, niflumic acid (NFA), dichloro‐diphenylamine 2‐carboxylic acid (DCDPC) and diisothiocyanato‐stilbene‐2,2′‐disulphonic acid (DIDS) on Ca 2+ ‐activated Cl − current ( I Cl(Ca) ) evoked by adding fixed intracellular calcium concentrations ([Ca 2+ ] i ) to the pipette solution were studied in rabbit pulmonary artery myocytes. With 250 and 500 n m [Ca 2+ ] i bath application of NFA (100 μ m ) increased inward current at negative potentials, but inhibited outward current at positive potentials. On wash out of NFA, I Cl(Ca) was greatly enhanced at all potentials. When external Na + ions were replaced by N ‐methyl‐ d ‐glucamine (NMDG + ) NFA still enhanced I Cl(Ca) at negative potentials but the increase of I Cl(Ca) on wash out was blocked. When the mean reversal potential ( E r ) of I Cl(Ca) was shifted to negative potentials by replacing external Cl − with SCN − , NFA increased inward current but blocked outward current suggesting that the effect of NFA is dependent on current flow. Inclusion of NFA in the pipette solution had no effect on I Cl(Ca) . Voltage jump experiments indicated that I Cl(Ca) displayed characteristic outward current relaxations at +70 mV and inward current relaxations at −80 mV that were abolished by NFA. DCDPC (100 μ m ) produced similar effects to NFA but 1 m m DIDS produced inhibition of I Cl(Ca) at both positive and negative potentials and there was no increase in current on wash out of DIDS. These results suggest that NFA and DCDPC, but not DIDS, simultaneously enhance and block I Cl(Ca) by binding to an external site, probably close to the mouth of the chloride channel.