Evidence for mediation by endothelium-derived hyperpolarizing factor of relaxation to bradykinin in the bovine isolated coronary artery independently of voltage-operated Ca~(2+) channels

摘要

1 The role of endothelium-derived hyperpolarizing factor and voltage-operated Ca~(2+) channels in mediating endothelium-dependent, N~G-nitro-L-arginine (L-NOARG; 100 μM) -resistant relaxations to bradykinin (BK), was examined in isolated rings of endothelium-intact bovine left anterior descending coronary artery. 2 Rings of artery were contracted isometrically to approximately 40% or their respective maximum contraction to 125 mM KCl Krebs solution (KPSS_(max)) with the thromboxane A_2-mimetic, U46619. Relaxations to BK and the endothelium-independent NO donor, S-nitroso-N-acetylpenicillamine (SNAP), were normalized as percentages of reversal of the initial contraction to U46619. All experiments were carried out in the presence of indomethacin (3 μM). 3 BK caused concentration-dependent relaxations [sensitivity (pEC_(50)) 9.88 ±0.05; maximum relaxation (R_(max)), 103.3 ± 0.5%] in U46619-contracted rings of bovine coronary artery. L-NOARG (100 μM) caused a significant (P < 0.01) 3 fold reduction in the sensitivity to BK (pEC_(50), 9.27 ± 0.11) without affecting the Rmax (101.8±2.3%). A similar, significant 3 fold reduction in sensitivity to BK with no change in R_(max) was observed after treatment with oxyhaemoglobin (20 μM; pEC_(50), 9.18 ± 0.13, P < 0.001) or a combination of oxyhaemoglobin (20 μM) and L-NOARG (100 μM; pEC_(50), 9.08 ±0.10, P < 0.001). Oxyhaemoglobin (20 μM) either alone or in combination with L-NOARG (100 μM) caused an approximate 600 fold decrease in the sensitivity to SNAP.