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 IC,, of 32.8 +/- 0.52 mu M ( mean +/- S.E.M., n = 5). Blockers of Ca2+-activated chloride channels, flufenamic acid (100 mu M) and 9-anthracene chloride (9-AC; 1 mM), and the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel blocker, glibenclamide (100 mu M), were without effect in this tissue (n = 3). 3. Under isobaric conditions at 20 mmHg, 37 degrees C, raising [K+](0) to 45 mM induced a constriction which was unaffected by 100 mu M NPPB (n = 4). In contrast, at 75 mmHg and 18-21 degrees C, 100 mu M 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 mu M (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 mu M (mean +/- S.E.M., n = 4). 5. Using whole-cell patch clamp, 100 mu M NPPB or 200 mu M 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.