New mediators in the biology of the ductus arteriosus:Lessons from the chicken embryo

The chicken embryo is an ideal model for the study of new hypotheses on the developmental biology of ductus arteriosus (DA). A unique characteristic of chicken DA is that it is the result of the fusion of two vessels with different embryological origins, morphologies, and functionalities. The pulmonary side (PulmDA) consists almost exclusively of neural crest-derived cells, shows the structure of a muscular artery, and responds to O2 with contraction whereas the aortic part is of mesodermal origin, shows the morphology of an elastic artery and relaxes in response to O2. In addition the two parts of the DA show marked differences in responsiveness to other contractile and relaxant agents. In mammals, the most accepted model of O2-induced DA constriction involves a rise in O2 modulating the function of the mitochondrial electron transport chain (the sensor), leading to an increased production of H2O2 (the mediator) that causes the inhibition of KV channels (the effector) with Rho kinase acting as another downstream effector of the O2-sensing system in the DA. In the chicken embryo, we verified the very same pathway, proving a conserved mechanism for O2 sensing/signaling in mammalian and nonmammalian DA. Moreover, we demonstrated a developmentally regulated response to O2, which is restricted to the mature PulmDA and involves parallel maturation of the three components: sensor, mediator, and effectors. Besides O2, we used the chicken embryo model to investigate the possible ductal effects of vasoactive mediators such as ceramide, H2S, isoprostanes, or platelet-derived vasoactive mediators

Mechanisms of U46619- and 5-HT-induced contraction of bovine pulmonary arteries: role of chloride ions

Background and purpose: Thromboxane A and 5-hydroxytryptamine (5-HT) are implicated in pulmonary hypertension. The involvement of chloride, voltage-operated calcium channels (VOCCs), store-operated calcium channels (SOCCs) and the Rho kinase in the contractile response of bovine pulmonary arteries (BPA) to the thromboxane A mimetic U46619 and 5-HT was investigated. Experimental approach: Endothelium-intact ring segments of BPA were mounted in Krebs/Henseleit buffer (37°C) under a tension of 2g and gassed with 95%O /5%CO . Key results: Depletion or removal of extracellular chloride, inhibition of chloride and SOCC, Na:K:2Cl, Cl/HCO , Rho kinase inhibited contractions to U46619. Combining Rho kinase inhibition and chloride channel blockade (with NPPB) almost abolished the contractions to U46619. In contrast 5-HT-induced contraction was inhibited by verapamil and mibefradil. Depletion of stored calcium with caffeine almost abolished the response to U46619 but not 5-HT. The contraction by the sarco(endo)plasmic reticulum Ca -ATPase inhibitor CPA was abolished by SOCC and chloride channel blockade (with NPPB) and by chloride depletion. Conclusions and implications: This study suggests that the contractile response of BPA to U46619 involves Rho kinase together with a chloride-sensitive mechanism, which does not involve VOCC but may have a role in calcium release and calcium entry via SOCC. In contrast contraction of the BPA by 5-HT appears to involve verapamil- and mibefradil-sensitive VOCC. This study may indicate that the use of calcium channel blockers in the management of pulmonary hypertension may not always be effective and that Rho kinase and chloride channels may be targets for the development of new therapies