Fig. 6.

The combination of 50 μM of compound 13 plus 10 μM bumetanide potentiates relaxation of ACh contractions in guinea pig tracheal rings by isoproterenol. A: the EC₅₀ of isoproterenol-mediated relaxation of an ACh contraction was shifted from 5.99 × 10⁻⁹ (vehicle) to 4.77 × 10⁻¹⁰ with a combination of 50 μM compound 13 and 10 μM bumetanide (P < 0.01). The 10 μM bumetanide or 50 μM compound 13 by themselves did not significantly shift relaxation by isoproterenol (2.51 × 10⁻⁹, 2.7 × 10⁻⁹ respectively, P > 0.05); n = 4–6. B: isoproterenol at 1 nM concentration relaxed ACh EC₅₀ 11.1% ± 4.5, whereas in combination with 10 μM bumetanide and 50 μM compound 13 the ACh EC₅₀ contraction relaxed to 86.8% ± 13.7, demonstrating a 7.8-fold difference in relaxation. The 10 μM bumetanide plus 50 μM compound 13 relaxed an ACh EC₅₀ contraction 50.5% ± 7.4 (calculated as percent of remaining ACh EC₅₀ contraction at 7 min). *P < 0.05, ***P < 0.001 compared with iso 1 nM; #P < 0.05; n = 6–10.