Mouse Pulmonary Arteries Research Articles

Comparison of Contractile Responses in Isolated Mouse Aorta and Pulmonary Artery

Transgenic mice are often used to study the physiologic role of a known gene. The design of experiments with transgenic mice usually does not take into account strain and sex differences, at least in isolated vessels. Therefore, we have compared the contractile response of isolated aortae and isolated pulmonary arteries of male and female mice of different strains (CD1, BL6, and DBA). Contractile stimulation was achieved by depolarization due to KCl, alpha1-adrenoceptor stimulation by phenylephrine and inhibition of protein phosphatase activity by cantharidin. In isolated aorta, strain-specific differences in contractility and sex-specific differences could be observed. The concentration of phenylephrine (PE) inducing half maximal contraction (EC50) was different between aortae from DBA male mice and the other strains tested. Phasic contractions of isolated aortic rings due to PE were seen in all mice except DBA male. In isolated pulmonary arteries, strain-specific differences and sex-specific differences could be observed. The EC50-values of PE were not different between all groups. Phasic contractions due to PE were only seen in pulmonary arteries from CD1 male and BL6 female. In conclusion, strain- and sex-specific differences should be considered in selecting mice used for transgenesis or gene targeting experiments.

Role of Membrane Potential in Endothelium-Dependent Relaxation of Isolated Mouse Main Pulmonary Artery

The physiology of smooth muscle and endothelial cells of a particular vascular bed and from different species differs from each other. Acetylcholine causes an endothelium-dependent relaxation of preconstricted pulmonary arteries from the rat. This relaxation is mediated by nitric oxide (NO) plus a yet-unidentified endothelium-derived hyperpolarizing factor, which relaxes the smooth muscles by hyperpolarizing them. Our aim is to test whether these observations could be generalized to the smooth muscle cells from the mouse pulmonary artery. Smooth muscle or endothelial cell membrane potential of strips of murine pulmonary artery were measured simultaneously with the force developed by the strip. Acetylcholine hyperpolarized the endothelial cells. However, acetylcholine did not induce an endothelium-dependent hyperpolarization of the smooth muscle, while it relaxed the strip in an endothelium-dependent manner. This relaxation was abolished by an inhibitor of NO synthesis, nitro-L-arginine. Moreover, nitroglycerin relaxed the strips without changing the membrane potential of the smooth muscle cells. Injection of Lucifer yellow into the endothelial cells and the smooth muscle cells did not show heterocellular dye coupling. Furthermore, electron microscopy did not show gap junction plate at the myoendothelial junctions. We conclude that in the mouse main pulmonary artery, NO alone is responsible for the acetylcholine-induced endothelium-dependent vasodilatation, whereas the phenomenon called endothelium-derived hyperpolizing factor is not present. Therefore, caution should be taken when comparing different animal models to study pulmonary circulation and its reactivity.

MIP‐2 activates AKT and RhoA in mouse aortic endothelial cells

ELR+ CXC chemokines are potent promoters of angiogenesis and have been shown to induce chemotaxis in endothelial cells (ECs). We reported previously that EC chemotaxis was markedly enhanced in systemic arterial ECs compared to pulmonary artery ECs in response to MIP-2, a potent proangiogenic ELR+ CXC chemokine ligand, which binds the G-protein coupled receptor, CXCR2. Also, we previously showed equivalent levels of CXCR2 expression in the two EC subtypes. However, differences in EC motility in response to MIP-2 may depend on differential utilization of signaling pathways. We studied the roles of protein kinase B/AKT and small GTPase RhoA in MIP-2 activation of mouse aortic (n=4) and pulmonary artery (n= 3) ECs. Additionally, since tissue hypoxia increases the angiogenic potential of systemic ECs, we studied ECs after hypoxia (24hrs)/reoxygenation (48hrs). MIP-2 (30min, 10 ng/ml) induced a greater increase in AKT phosphorylation (pAKT) in aortic ECs (33%) compared to pulmonary artery ECs (17%). Hypoxia/reoxygenation increased pAKT in aortic ECs (46%) but did not alter pulmonary artery EC pAKT. Only aortic ECs showed an increase in RhoA activation (40%) after MIP-2 treatment and hypoxia/ reoxygenation further increased RhoA activation after MIP-2 in aortic ECs (71%). These results confirm that AKT and RhoA are involved in MIP-2 induced activation of a proangiogenic phenotype, preferentially in aortic ECs. Supported by HL71605

Pulmonary vasoconstrictor action of KCNQ potassium channel blockers.

BackgroundKCNQ channels have been widely studied in the nervous system, heart and inner ear, where they have important physiological functions. Recent reports indicate that KCNQ channels may also be expressed in portal vein where they are suggested to influence spontaneous contractile activity. The biophysical properties of K+ currents mediated by KCNQ channels resemble a current underlying the resting K+ conductance and resting potential of pulmonary artery smooth muscle cells. We therefore investigated a possible role of KCNQ channels in regulating the function of pulmonary arteries by determining the ability of the selective KCNQ channel blockers, linopirdine and XE991, to promote pulmonary vasoconstriction.MethodsThe tension developed by rat and mouse intrapulmonary or mesenteric arteries was measured using small vessel myography. Contractile responses to linopirdine and XE991 were measured in intact and endothelium denuded vessels. Experiments were also carried out under conditions that prevent the contractile effects of nerve released noradrenaline or ATP, or block various Ca2+ influx pathways, in order to investigate the mechanisms underlying contraction.ResultsLinopirdine and XE991 both contracted rat and mouse pulmonary arteries but had little effect on mesenteric arteries. In each case the maximum contraction was almost as large as the response to 50 mM K+. Linopirdine had an EC50 of around 1 μM and XE991 was almost 10-fold more potent. Neither removal of the endothelium nor exposure to phentolamine or α,β-methylene ATP, to block α1-adrenoceptors or P2X receptors, respectively, affected the contraction. Contraction was abolished in Ca2+-free solution and in the presence of 1 μM nifedipine or 10 μM levcromakalim.ConclusionThe KCNQ channel blockers are potent and powerful constrictors of pulmonary arteries. This action may be selective for the pulmonary circulation as mesenteric arteries showed little response. The results imply that the drugs act directly on smooth muscle cells and contraction requires voltage-dependent Ca2+ influx. It is concluded that the drugs probably act by blocking KCNQ channels in pulmonary artery myocytes, leading to membrane depolarization and Ca2+ influx through L-type Ca2+ channels. This implies a functional role for KCNQ channels in regulating the resting membrane potential of pulmonary artery myocytes.

Linked mechanical and biological aspects of remodeling in mouse pulmonary arteries with hypoxia-induced hypertension

Right heart failure due to pulmonary hypertension causes significant morbidity and mortality. To study the linked vascular mechanical and biological changes that are induced by pulmonary hypertension, we mechanically tested isolated left main pulmonary arteries from mice exposed to chronic hypobaric hypoxia and performed histological assays on contralateral vessels. In isolated vessel tests, hypoxic vessels stretched less in response to pressure than controls at all pressure levels. Given the short length and large diameter of the pulmonary artery, the tangent Young's modulus could not be measured; instead, an effective elastic modulus was calculated that increased significantly with hypoxia [(280 kPa (SD 53) and 296 kPa (SD 50) for 10 and 15 days, respectively, vs. 222 kPa (SD 35) for control; P < 0.02)]. Hypoxic vessels also had higher damping coefficients [(0.063 (SD 0.017) and 0.054 (SD 0.014) for 10 and 15 days, respectively, vs. 0.033 (SD 0.016) for control; P < 0.002)], indicating increased energy dissipation. The increased stiffness with hypoxia correlated with an increase in collagen thickness (percent collagen multiplied by wall thickness) as well as the sum of elastin and collagen thicknesses measured histologically in the artery wall. These results highlight the mechanobiological changes in the pulmonary vasculature that occur in response to hypoxia-induced pulmonary hypertension. Furthermore, they demonstrate significant vascular mechanical and biological changes that would increase pulmonary vascular impedance, leading to right heart failure.

Human cardiovascular adjustments to exercise and thermal stress.

Human cardiovascular adjustments to exercise and thermal stress.