Modification of gating of an airway epithelial chloride channel by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB).
5-Nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) has been shown to produce a reduction in channel open probability in a number of epithelial chloride channels. We have investigated its action on a calcium-dependent airway epithelial chloride channel, which shows voltage-dependent gating following incorporation into planar phospholipid bilayers. Since the channel demonstrates a distinct subconductance state at approximately one-third of the fully open level, both 50 and 20% threshold analysis (TA) have been used to describe channel kinetics. Lifetime analysis using 50% TA in the absence of NPPB showed that two open and three closed lifetimes provided the optimal fit. Similar analysis using 20% TA required only two closed lifetimes and allowed for tentative assignment of tau values to either substate or fully closed events. NPPB (10-100 microM) produced a concentration-related shift of the normal voltage dependence of gating, with more negative holding potentials being required to produce a given channel open probability than in the absence of NPPB. Ten microM NPPB produced a similar shift in lifetime values. However, addition of 50 microM NPPB produced a unique, single open lifetime. No evidence was found for NPPB acting as a direct voltage-dependent blocker of chloride conductance.
Alton
E W
EW
Ion Transport Laboratory, National Heart and Lung Institute, London, United Kingdom.
Williams
A J
AJ
D000818:Animals; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects*; D007473:Ion Channels / Q000187:drug effects* / Q000378:metabolism; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000187:drug effects* / Q000378:metabolism; D009579:Nitrobenzoates / Q000494:pharmacology*; D012756:Sheep; D014132:Trachea / Q000187:drug effects* / Q000378:metabolism
D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008565:Membrane Proteins; D009579:Nitrobenzoates; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid