Summary
5-Nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) has been shown to produce a reduction in channel open probabilty i n 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 μm) 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 μM NPPB produced a similar shift in lifetime values. However, addition of 50 μm NPPB produced a unique, single open lifetime. No evidence was found for NPPB acting as a direct voltage-dependent blocker of chloride conductance.
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We are grateful to Prof. R. Greger for the generous gift of the NPPB, to Dr. Andrew Tinker for advice and useful discussion, and to the CF Research Trust and British Lung Foundation for supporting the study. EWFWA was supported by an MRC Training Fellowship.
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Alton, E.W.F.W., Williams, A.J. Modification of gating of an airway epithelial chloride channel by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB). J. Membarin Biol. 128, 141–151 (1992). https://doi.org/10.1007/BF00231887
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DOI: https://doi.org/10.1007/BF00231887