Abstract
We investigated the effects of the Cl− channel blockers niflumic acid, 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) and 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS) on endothelin-1 (ET-1)-induced constriction of rat small pulmonary arteries (diameter 100–400 μm) in vitro, following endothelium removal. ET-1 (30 nM) induced a sustained constriction of rat pulmonary arteries in physiological salt solution. Arteries preconstricted with ET-1 were relaxed by niflumic acid (IC50: 35.8 μM) and NPPB (IC50: 21.1 μM) in a reversible and concentration-dependent manner. However, at concentrations known to block Ca++-activated Cl− channels, DIDS (≤500 μM) had no effect on the ET-1-induced constriction. Similar results were obtained when pulmonary arteries were preincubated with these Cl− channel blockers. When l-type Ca++ channels were blocked by nifedipine (10 μM), the ET-1-induced (30 nM) constriction was inhibited by only 5.8%. However, niflumic acid (30 μM) and NPPB (30 μM) inhibited the ET-1-induced constriction by ∼53% and ∼60%, respectively, both in the continued presence of nifedipine and in Ca++-free physiological salt solution. The Ca++ ionophore A23187 (10 μM) also evoked a sustained constriction of pulmonary arteries. Surprisingly, the A23187-induced constriction was also inhibited in a reversible and concentration-dependent manner by niflumic acid (IC50: 18.0 μM) and NPPB (IC50: 8.8 μM), but not by DIDS (≤500 μM). Our data suggest that the primary mechanism by which niflumic acid and NPPB inhibit pulmonary artery constriction is independent of Cl− channel blockade. One possibility is that these compounds may block the Ca++-dependent contractile processes.
Footnotes
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Send reprint requests to: Kenichi Kato, University Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, UK. E-mailKen.Kato{at}pharm.ox.ac.uk
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↵1 This research was supported by the British Heart Foundation, the Medical Research Council, and the Royal Society.
- Abbreviations:
- ET-1
- endothelin-1
- STXS6c
- sarafotoxin S6c
- NPPB
- 5-nitro-2-(3-phenylpropylamino)-benzoic acid
- DIDS
- 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid
- VGCC
- voltage-gated Ca++
- ICl(Ca)
- Ca++-activated Cl− current
- IKV
- delayed rectifier K+current
- Received April 23, 1998.
- Accepted September 14, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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