Role of membrane potential in endothelium-dependent relaxation of isolated mouse main pulmonary artery

T-type voltage gated calcium channels are involved in endothelium-dependent relaxation of mice pulmonary artery

In pulmonary arterial endothelial cells, Ca²⁺ channels and intracellular Ca²⁺ concentration ([Ca²⁺]_i) control the release of vasorelaxant factors such as nitric oxide and are involved in the regulation of pulmonary arterial blood pressure. The present study was undertaken to investigate the implication of T-type voltage-gated Ca²⁺ channels (T-VGCCs, Ca_v3.1 channel) in the endothelium-dependent relaxation of intrapulmonary arteries. Relaxation was quantified by means of a myograph in wild type and Ca_v3.1^-/- mice. Endothelial [Ca²⁺]_i and NO production were measured, on whole vessels, with the fluo-4 and DAF-fm probes. Acetylcholine (ACh) induced a nitric oxide- and endothelium-dependent relaxation that was significantly reduced in pulmonary arteries from Ca_v3.1^-/- compared to wild type mice as well as in the presence of T-VGCC inhibitors (NNC 55-0396 or mibefradil). ACh also increased endothelial [Ca²⁺]_i and NO production that were both reduced in Ca_v3.1^-/- compared to wild type mice or in the presence of T-VGCC inhibitors. Immunofluorescence labeling revealed the presence of Ca_v3.1 channels in endothelial cells that co-localized with endothelial nitric oxide synthase in arteries from wild type mice. TRPV4-, beta2 adrenergic- and nitric oxide donors (SNP)-mediated relaxation were not altered in Ca_v3.1^-/- compared to wild type mice. Finally, in chronically hypoxic mice, a model of pulmonary hypertension, ACh relaxation was reduced but still depended on Ca_v3.1 channels activity. The present study thus demonstrates that T-VGCCs, mainly Ca_v3.1 channel, contribute to intrapulmonary vascular reactivity in mice by controlling endothelial [Ca²⁺]_i and ACh-mediated relaxation.

Perinatal nitric oxide therapy prevents adverse effects of perinatal hypoxia on the adult pulmonary circulation

Adverse events in utero are associated with the occurrence of chronic diseases in adulthood. We previously demonstrated in mice that perinatal hypoxia resulted in altered pulmonary circulation in adulthood, with a decreased endothelium-dependent relaxation of pulmonary arteries, associated with long-term alterations in the nitric oxide (NO)/cyclic GMP pathway. The present study investigated whether inhaled NO (iNO) administered simultaneously to perinatal hypoxia could have potential beneficial effects on the adult pulmonary circulation. Indeed, iNO is the therapy of choice in humans presenting neonatal pulmonary hypertension. Long-term effects of neonatal iNO therapy on adult pulmonary circulation have not yet been investigated. Pregnant mice were placed in hypoxia (13% O₂) with simultaneous administration of iNO 5 days before delivery until 5 days after birth. Pups were then raised in normoxia until adulthood. Perinatal iNO administration completely restored acetylcholine-induced relaxation, as well as endothelial nitric oxide synthase protein content, in isolated pulmonary arteries of adult mice born in hypoxia. Right ventricular hypertrophy observed in old mice born in hypoxia compared to controls was also prevented by perinatal iNO treatment. Therefore, simultaneous administration of iNO during perinatal hypoxic exposure seems able to prevent adverse effects of perinatal hypoxia on the adult pulmonary circulation.

Wall shear stress effects on endothelial-endothelial and endothelial-smooth muscle cell interactions in tissue engineered models of the vascular wall

Vascular functions are affected by wall shear stresses (WSS) applied on the endothelial cells (EC), as well as by the interactions of the EC with the adjacent smooth muscle cells (SMC). The present study was designed to investigate the effects of WSS on the endothelial interactions with its surroundings. For this purpose we developed and constructed two co-culture models of EC and SMC, and compared their response to that of a single monolayer of cultured EC. In one co-culture model the EC were cultured on the SMC, whereas in the other model the EC and SMC were cultured on the opposite sides of a membrane. We studied EC-matrix interactions through focal adhesion kinase morphology, EC-EC interactions through VE-Cadherin expression and morphology, and EC-SMC interactions through the expression of Cx43 and Cx37. In the absence of WSS the SMC presence reduced EC-EC connectivity but produced EC-SMC connections using both connexins. The exposure to WSS produced discontinuity in the EC-EC connections, with a weaker effect in the co-culture models. In the EC monolayer, WSS exposure (12 and 4 dyne/cm² for 30 min) increased the EC-EC interaction using both connexins. WSS exposure of 12 dyne/cm² did not affect the EC-SMC interactions, whereas WSS of 4 dyne/cm² elevated the amount of Cx43 and reduced the amount of Cx37, with a different magnitude between the models. The reduced endothelium connectivity suggests that the presence of SMC reduces the sealing properties of the endothelium, showing a more inflammatory phenotype while the distance between the two cell types reduced their interactions. These results demonstrate that EC-SMC interactions affect EC phenotype and change the EC response to WSS. Furthermore, the interactions formed between the EC and SMC demonstrate that the 1-side model can simulate better the arterioles, while the 2-side model provides better simulation of larger arteries.

Perinatal hypoxia enhances cyclic adenosine monophosphate-mediated BKCa channel activation in adult murine pulmonary artery

Exposure to perinatal hypoxia results in alteration of the adult pulmonary circulation, which is linked among others to alterations in K(+) channels in pulmonary artery (PA) smooth muscle cells. In particular, large conductance Ca(2+)-activated K(+) (BK(Ca)) channels protein expression and activity were increased in adult PA from mice born in hypoxia compared with controls. We evaluated long-term effects of perinatal hypoxia on the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway-mediated activation of BK(Ca) channels, using isoproterenol, forskolin, and dibutyryl-cAMP. Whole-cell outward current was higher in pulmonary artery smooth muscle cells from mice born in hypoxia compared with controls. Spontaneous transient outward currents, representative of BK(Ca) activity, were present in a greater proportion in pulmonary artery smooth muscle cells of mice born in hypoxia than in controls. Agonists induced a greater relaxation in PA of mice born in hypoxia compared with controls, and BK(Ca) channels contributed more to the cAMP/PKA-mediated relaxation in case of perinatal hypoxia. In summary, perinatal hypoxia enhanced cAMP-mediated BK(Ca) channels activation in adult murine PA, suggesting that this pathway could be a potential target for modulating adult pulmonary vascular tone after perinatal hypoxia.

Myoendothelial gap junctional signaling induces differentiation of pulmonary arterial smooth muscle cells

Myoendothelial gap junctions are involved in regulating systemic arterial smooth muscle cell phenotype and function, but their role in the regulation of pulmonary arterial smooth muscle cell (PASMC) phenotype is unknown. We therefore investigated in cocultured pulmonary arterial endothelial cells (PAECs) and PASMCs whether myoendothelial gap junctional signaling played a role in PAEC-dependent regulation of PASMC phenotype. Rat PAECs and PASMCs were cocultured on opposite sides of a porous Transwell membrane that permitted formation of heterotypic cell-cell contacts. Immunostaining showed expression of the gap junctional protein connexin 43 (Cx43) on projections extending into the membrane from both cell types. Dye transfer exhibited functional gap junctional communication from PAECs to PASMCs. PASMCs cocultured with PAECs had a more contractile-like phenotype (spindle shape and increased expression of the contractile proteins myosin heavy chain, H1-calponin, and α-smooth muscle cell-actin) than PASMCs cocultured with PASMCs or cocultured without direct contact with PAECs. Transforming growth factor (TGF)-β1 signaling was activated in PASMCs cocultured with PAECs, and the PASMC differentiation was inhibited by TGF-β type I receptor blockade. Inhibition of gap junctional communication pharmacologically or by knock down of Cx43 in PAECs blocked TGF-β signaling and PASMC differentiation. These results implicate myoendothelial gap junctions as a gateway for PAEC-derived signals required for maintaining TGF-β-dependent PASMC differentiation. This study identifies an alternative pathway to paracrine signaling to convey regulatory signals from PAECs to PASMCs and raises the possibility that dysregulation of this direct interaction is involved in the pathogenesis of hypertensive pulmonary vascular remodeling.

The myoendothelial junction: breaking through the matrix?

Within the vasculature, specialized cellular extensions from endothelium (and sometimes smooth muscle) protrude through the extracellular matrix where they interact with the opposing cell type. These structures, termed myoendothelial junctions, have been cited as a possible key element in the control of several vascular physiologies and pathologies. This review will discuss observations that have led to a focus on the myoendothelial junction as a cellular integration point in the vasculature for both homeostatic and pathological conditions and as a possible independent signaling entity. We will also highlight the need for novel approaches to studying the myoendothelial junction in order to comprehend the cellular biology associated with this structure.

Muscarinic receptor M1 and phosphodiesterase 1 are key determinants in pulmonary vascular dysfunction following perinatal hypoxia in mice

Perinatal adverse events such as limitation of nutrients or oxygen supply are associated with the occurrence of diseases in adulthood, like cardiovascular diseases and diabetes. We investigated the long-term effects of perinatal hypoxia on the lung circulation, with particular attention to the nitric oxide (NO)/cGMP pathway. Mice were placed under hypoxia in utero 5 days before delivery and for 5 days after birth. Pups were then bred in normoxia until adulthood. Adults born in hypoxia displayed an altered regulation of pulmonary vascular tone with higher right ventricular pressure in normoxia and increased sensitivity to acute hypoxia compared with controls. Perinatal hypoxia dramatically decreased endothelium-dependent relaxation induced by ACh in adult pulmonary arteries (PAs) but did not influence NO-mediated endothelium-independent relaxation. The M(3) muscarinic receptor was implicated in the relaxing action of ACh and M(1) muscarinic receptor (M(1)AChR) in its vasoconstrictive effects. Pirenzepine or telenzepine, two preferential inhibitors of M(1)AChR, abolished the adverse effects of perinatal hypoxia on ACh-induced relaxation. M(1)AChR mRNA expression was increased in lungs and PAs of mice born in hypoxia. The phosphodiesterase 1 (PDE1) inhibitor vinpocetine also reversed the decrease in ACh-induced relaxation following perinatal hypoxia, suggesting that M(1)AChR-mediated alteration of ACh-induced relaxation is due to the activation of calcium-dependent PDE1. Therefore, perinatal hypoxia leads to an altered pulmonary circulation in adulthood with vascular dysfunction characterized by impaired endothelium-dependent relaxation and M(1)AChR plays a predominant role. This raises the possibility that muscarinic receptors could be key determinants in pulmonary vascular diseases in relation to "perinatal imprinting."

Perinatal hypoxia triggers alterations in K+ channels of adult pulmonary artery smooth muscle cells

Adverse events during the perinatal period, like hypoxia, have been associated with adult diseases. In pulmonary vessels, K(+) channels play an important role in the regulation of vascular tone. In the fetus, Ca(2+)-activated K(+) channels (K(Ca)) are predominant, whereas from birth voltage-gated K(+) channels (K(V)) prevail in the adult. We postulated that perinatal hypoxia could alter this maturational shift and influence regulation of pulmonary vascular tone in relation to K(+) channels in adulthood. We evaluated the effects of perinatal hypoxia on K(V) and K(Ca) channels in the adult main pulmonary artery (PA) using a murine model. Electrophysiological measurements showed a greater outward current in PA smooth muscle cells of mice born in hypoxia than in controls. In controls, only K(V) channels contributed to this current, whereas in mice born in hypoxia both K(V) and K(Ca) channels were implicated. K(V) channel activity was even higher in mice born in hypoxia than in controls. Therefore, perinatal hypoxia results in increased K(Ca) and K(V) channel activity in adult PA. Moreover, PA of adults born in hypoxia displayed higher large-conductance K(Ca) alpha-subunit and K(V)1.5 alpha-subunit protein expression than controls. Interestingly, relaxation induced by nitric oxide (NO) donors [S-nitroso-N-acetyl-D,l-penicillamine, 2-(N,N-diethylamino)-diazenolate-2-oxide] in isolated PA of control mice was not mediated by K(Ca) channels and only slightly by K(V) channels, whereas following perinatal hypoxia both K(Ca) and K(V) channels contributed to this relaxation. Thus perinatal hypoxia results in altered expression and activity of different K(+) channels in the adult main PA, which could contribute to modifications of pulmonary vasoreactivity.