Non-specificity of chloride channel blockers in rat cerebral arteries: block of the L-type calcium channel.
1. The effects of chloride channel blockers on pressure-induced constriction, K(+)-induced force, and whole-cell calcium channel currents were tested in rat cerebral arteries using isobaric and isometric myography, and patch clamp. 2. Under isobaric conditions at 75 mmHg, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), a chloride channel blocker, reversibly depressed the myogenic constriction with an IC50 of 32.8 +/- 0.52 microM (mean +/- S.E.M., n = 5). Blockers of Ca(2+)-activated chloride channels, flufenamic acid (100 microM) and 9-anthracene chloride (9-AC; 1 mM), and the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel blocker, glibenclamide (100 microM), were without effect in this tissue (n = 3). 3. Under isobaric conditions at 20 mmHg, 37 degrees C, raising [K+]o to 45 mM induced a constriction which was unaffected by 100 microM NPPB (n = 4). In contrast, at 75 mmHg and 18-21 degrees C, 100 microM NPPB completely and reversibly blocked a 45 mM K(+)-induced constriction (n = 3). 4. Under isometric conditions, NPPB reversibly depressed a 45 mM K(+)-induced force with an IC50 of 10.0 +/- 0.76 microM (mean +/- S.E.M., n = 5). Indanyloxyacetic acid 94 (IAA-94), another chloride channel blocker, depressed the K(+)-induced force with an IC50 of 17.0 +/- 1.2 microM (mean +/- S.E.M., n = 4). 5. Using whole-cell patch clamp, 100 microM NPPB or 200 microM IAA-94 blocked calcium channel currents carried by 10 mM Ba2+ by 79.1 +/- 1.7 and 39.8 +/- 7.0%, respectively (mean +/- S.E.M., n = 6). 6. In summary, chloride channel blockers depress calcium channel currents in rat cerebral arteries, which could contribute to a reduction in myogenic contraction.
Doughty
J M
JM
Department of Physiology, University of Bristol, UK.
Miller
A L
AL
Langton
P D
PD
D000818:Animals; D001464:Barium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002536:Cerebral Arteries / Q000187:drug effects / Q000378:metabolism*; D018118:Chloride Channels / Q000037:antagonists & inhibitors*; D004594:Electrophysiology; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008564:Membrane Potentials / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009213:Myography; D009579:Nitrobenzoates / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar
D002121:Calcium Channel Blockers; D018118:Chloride Channels; D009579:Nitrobenzoates; D001464:Barium; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid