Hypoxia sensing in the fetal chicken femoral artery is mediated by the mitochondrial electron transport chain

Zoer B, Cogolludo AL, Perez-Vizcaino F, De Mey JG, Blanco CE, Villamor E. Hypoxia sensing in the fetal chicken femoral artery is mediated by the mitochondrial electron transport chain. Am J Physiol Regul Integr Comp Physiol 298: R1026-R1034, 2010. First published January 20, 2010; doi: 10.1152/ajpregu.00500.2009.Vascular hypoxia sensing is transduced into vasoconstriction in the pulmonary circulation, whereas systemic arteries dilate. Mitochondrial electron transport chain (mETC), reactive O-2 species (ROS), and K+ channels have been implicated in the sensing/signaling mechanisms of hypoxic relaxation in mammalian systemic arteries. We aimed to investigate their putative roles in hypoxia-induced relaxation in fetal chicken (19 days of incubation) femoral arteries mounted in a wire myograph. Acute hypoxia (PO2 similar to 2.5 kPa) relaxed the contraction induced by norepinephrine (1 mu M). Hypoxia-induced relaxation was abolished or significantly reduced by the mETC inhibitors rotenone (complex I), myxothiazol and antimycin A (complex III), and NaN3 (complex IV). The complex II inhibitor 3-nitroproprionic acid enhanced the hypoxic relaxation. In contrast, the relaxations mediated by acetylcholine, sodium nitroprusside, or forskolin were not affected by the mETC blockers. Hypoxia induced a slight increase in ROS production (as measured by 2,7-dichlorofluorescein-fluorescence), but hypoxia-induced relaxation was not affected by scavenging of superoxide (polyethylene glycol-superoxide dismutase) or H2O2 (polyethylene glycol-catalase) or by NADPH-oxidase inhibition (apocynin). Also, the K+ channel inhibitors tetraethylammonium (nonselective), diphenyl phosphine oxide-1 (voltage-gated K+ channel 1.5), glibenclamide (ATP-sensitive K+ channel), iberiotoxin (large-conductance Ca2+-activated K+ channel), and BaCl2 (inward-rectifying K+ channel), as well as ouabain (Na+-K+-ATPase inhibitor) did not affect hypoxia-induced relaxation. The relaxation was enhanced in the presence of the voltage-gated K+ channel blocker 4-aminopyridine. In conclusion, our experiments suggest that the mETC plays a critical role in O-2 sensing in fetal chicken femoral arteries. In contrast, hypoxia-induced relaxation appears not to be mediated by ROS or K+ channels

Effects of nicorandil as compared to mixtures of sodium nitroprusside and levcromakalim in isolated rat aorta

1. The contribution of the relaxant mechanisms of nicorandil (NIC) were analysed by comparing its effects with those of sodium nitroprusside (SNP), levcromakalim (LEM) and mixtures (1:10, 1:30 and 1:100) of SNP:LEM in isolated endothelium-denuded rat aorta. 2. In rings precontracted with KCl (25 mM), the relative inhibitory potency of the soluble guanylate cyclase inhibitor ODQ and the K(ATP) channel inhibitor glibenclamide (GLI) on SNP:LEM mixtures showed a good correlation with the relative proportion of SNP and LEM in the mixtures. Furthermore, the degree of the inhibition by ODQ and GLI of the effects of the 1:30 SNP:LEM mixture varied as a function of the relative potency of SNP and LEM in KCl-, noradrenaline- (NA) or NA plus nifedipine-treated arteries. 3. The inhibitory effects of ODQ, GLI and ODQ plus GLI on NIC-induced relaxation was similar to that for the 1:30 SNP:LEM mixture in NA plus nifedipine-contracted arteries, but the inhibition of GLI or ODQ plus GLI was smaller in KCl-contracted arteries. 4. In conclusion, the relative importance of activation of the cyclic GMP pathway and K(ATP) channel opening in mixtures of SNP and LEM could be predicted by the proportion of the drugs in the mixtures and by the relative potency of SNP vs LEM in different experimental conditions. Furthermore, the present results suggest that besides these two mechanisms, a third ODQ- and GLI-insensitive mechanism, possibly involving Ca(2+) channel blockade, also participates in the relaxant effects of NIC in KCl-induced contractions

Vasodilator effects of sodium nitroprusside, levcromakalim and their combination in isolated rat aorta

1. The endothelial modulation of the relaxant responses to the nitric oxide (NO) donor sodium nitroprusside (SNP) and the K(ATP) channel opener levcromakalim (LEM) and the interactions between these agents were analysed in isolated rat aorta. 2. LEM-induced relaxation was unchanged by endothelium removal or by the presence of L-NAME (10(−4) M) or ODQ (10(−6) M). In contrast, in KCl- (25 mM), but not in noradrenaline- (NA, 10(−6) M) contracted arteries, SNP-induced relaxation was augmented by endothelium removal but not by L-NAME, indomethacin, glibenclamide nor charybdotoxin plus apamin. 3. The isobolographic analysis of the interactions between exogenously activated K(ATP) channels and cyclic GMP using mixtures of SNP and LEM revealed that there were no interactions between both drugs at the proportions at which both drugs were active. However, the points for the SNP : LEM mixtures in proportions 10 : 1 and 1 : 10,000 (i.e. at concentrations at which LEM and SNP were inactive, respectively) fell significantly above the line of additivity indicating that there were negative interactions between both drugs at these selected proportions (about 5- and 2 fold inhibition, respectively). The former interaction was sensitive to glibenclamide, whereas the latter was insensitive ODQ. The magnitude of the 10 : 1 SNP : LEM interaction was smaller in endothelium-intact arteries and was absent in arteries stimulated by NA. 4. In conclusion, the relaxations induced by LEM and SNP were additive. However, the presence of endothelium and low concentrations of LEM inhibited SNP-induced relaxation. Both inhibitory effects were not additive and were only observed in KCl- and not in NA-contracted aortae