Enhanced expression of contractile endothelin ETB receptors in rat coronary artery after organ culture

Doxorubicin alters G-protein coupled receptor-mediated vasocontraction in rat coronary arteries

Doxorubicin (Doxo)-associated cardio-and vasotoxicity has been recognised as a serious complication of cancer chemotherapy. The purpose of this novel paper was to determine the effect of Doxo on G-protein coupled receptor (GPCR)-mediated vasocontraction located on vascular smooth muscle cells. Rat left anterior descending artery segments were incubated for 24 h with 0.5 µM Doxo. The vasocontractile responses by activation of endothelin receptor type A (ETA) and type B (ETB), serotonin receptor 1B (5-HT1B) and thromboxane A2 prostanoid receptor (TP) were investigated by a sensitive myography using specific agonists, while the specificity of the GPCR agonists was verified by applying selective antagonists (i.e. ETA and ETB agonist = 10- 14-10- 7.5 M endothelin-1 (ET-1); ETA antagonist = 10 µM BQ123; ETB agonists = 10- 14-10- 7.5 M sarafotoxin 6c (S6c) and ET-1; ETB antagonist = 0.1 µM BQ788; 5-HT1B agonist = 10- 12-10- 5.5 M 5-carboxamidotryptamine (5-CT); 5-HT1B antagonist = 1 µM GR55562; TP agonist = 10- 12-10- 6.5 M U46619; TP antagonist = 1 µM Seratrodast). Our results show that 0.5 µM Doxo incubation of LAD segments leads to an increased VSMC vasocontraction through the ETB, 5-HT1B and TP GPCRs, with a 2.2-fold increase in ETB-mediated vasocontraction at 10- 10.5 M S6c, a 2.0-fold increase in 5-HT1B-mediated vasocontraction at 10- 5.5 M 5-CT, and a 1.3-fold increase in TP-mediated vasocontraction at 10- 6.5 M U46619. Further studies unravelling the involvement of intracellular GPCR signalling pathways will broaden our understanding of the Doxo-induced vasotoxicity, and thus pave the way to mitigate the adverse effects by potential implementation of adjunct therapy options.

Gonadal function protects against organ culture-induced vascular damage. Involvement of prostanoids

Androgen deprivation induces vascular dysfunction in which altered release and action of prostanoids has been extensively studied. On the other hand, the vascular organ-culture system has been reported as a valid model for phenotypic changes that occur in several cardiovascular pathologies. Since there are no studies analyzing the impact of androgenic loss on vascular vulnerability during induced vascular damage, the objective of this study was to analyze the possible preventive role of male sex hormones on the organ culture-induced vascular damage in rat aorta. The link to possible changes in gross structure was also analyzed. For this purpose, fresh and 20 h-cultured aortic arterial segments from intact and orchidectomized rats were used to analyze: (i) the release and vasomotor effect of the thromboxane A₂ (TXA₂), prostaglandin (PG) E₂, PGF_2α and PGI₂; (ii) the vasodilator response induced by acetylcholine (ACh) as well as the involvement of prostanoids, in particular TXA₂, in the ACh-induced response; (iii) the effect of activation of thromboxane/prostaglandin (TP) receptors on the ACh-induced response; and (iv) the vascular structure. The results showed that organ culture: i) increased production of prostanoids; ii) increased prostanoids-induced vasomotor responses; iii) decreased ACh-induced relaxation after incubation with indomethacin, a blocker of cyclooxygenases; iv) increased the ACh-induced relaxation after incubation with the TXA₂ synthase inhibitor, furegrelate, more in arteries from orchidectomized rats than in those of intact rats; v) diminished ACh-induced relaxation after U-46619 incubation only in arteries from orchidectomized rats; and vi) preserved the integrity of the different vascular layers. These results showed the protective role of male sex hormones against the induced vascular damage, since a decreased deleterious effect of prostanoids, in particular that of TXA₂, was observed in arteries from rats with intact gonadal function.

Endothelin-1 and Endothelin-3 Regulate Endothelin Receptor Expression in Rat Coronary Arteries

In ischaemic hearts, endothelin (ET) levels are increased, and vasoconstrictor responses to ET-1 are greatly enhanced. We previously reported that ETB receptors are up-regulated in the smooth muscle layer of coronary arteries after myocardial ischaemia-reperfusion and that the MEK-ERK1/2 signalling pathway is involved in ETB receptor up-regulation. Whether ETs are directly involved in receptor regulation has not been determined. We suggest that ET-1 and ET-3 alter the expression/activity of ET receptors in coronary vascular smooth muscle cells. Vasoconstrictor responses were studied in endothelium-denuded coronary artery segments from rats that were subjected to experimental ischaemia-reperfusion or in organ-cultured segments. Post-ischaemic and cultured coronary arteries exhibited similar increased sensitivity to ET-3. ETA receptor-mediated vasoconstriction was dominant in fresh and non-ischaemic arteries. Organ culture significantly up-regulated ETB receptors and down-regulated ETA receptor expression. Co-incubation with ET-1 (1 nM) or ET-3 (100 nM) induced further down-regulation of the ETA receptor mRNA, while the function and protein level of ETA remained unchanged. ET-3 (100 nM) further up-regulated ETB receptor mRNA and proteins but abolished ETB receptor-mediated vasoconstriction, suggesting a desensitization of ETB receptors that was not observed with ET-3 (1 nM). In conclusion, ET-1, which is the most prevalent isoform in the cardiovascular system, induces down-regulation of ETA receptor expression without changing ETA or ETB receptor function or protein levels. Intermediate concentrations of ET-3 had an effect that was similar to that of ET-1, such that high concentrations of ET-3 (100 nM) up-regulated the ETB receptor at the gene and protein levels but switched off the function of the ETB receptors via desensitization.

Increased endothelin 1 type B receptors in nasal lesions of patients with granulomatosis with polyangiitis

BACKGROUND

Endothelin 1 (ET-1) is a locally produced vasoactive peptide with proinflammatory capabilities. Systemic levels of ET-1 seem elevated in granulomatosis with polyangiitis (GPA). The aim of this study was to examine the involvement of the endothelin system in patients with GPA using nasal mucosal biopsies.

METHODS

Formalin-fixed and paraffin-embedded nasal mucous membranes from eight patients with GPA and eight controls were analyzed for ET-1 type A receptor (ETAR) and type B receptor (ETBR) expression using immunohistochemistry.

RESULT

ETAR immunostaining was localized only to a few inflammatory cells and to multinucleate giant cells (MGCs) in the nasal mucosa in GPA subjects. Intense ETBR immunostaining was localized to lymphocytes and MGC in the nasal granulomatous lesions in GPA. CD3(+), CD4(+), CD8(+), and CD68(+) lymphocytes expressed ETBRs in GPA subjects.

CONCLUSION

This observation shows that ETBR(+) lymphocyte expression predominates in nasal granulomatous lesions in GPA compared with ETAR. ETBR immunostaining is located to T cells, CD68(+) cells, and MGCs. ETBR may play an active role in the progression of granulomatous lesions in GPA.

Upregulation of 5-hydroxytryptamine receptor signaling in coronary arteries after organ culture

Background

5-Hydroxytryptamine (5-HT) is a powerful constrictor of coronary arteries and is considered to be involved in the pathophysiological mechanisms of coronary-artery spasm. However, the mechanism of enhancement of coronary-artery constriction to 5-HT during the development of coronary artery disease remains to be elucidated. Organ culture of intact blood-vessel segments has been suggested as a model for the phenotypic changes of smooth muscle cells in cardiovascular disease.

Methodology/Principal Findings

We wished to characterize 5-HT receptor-induced vasoconstriction and quantify expression of 5-HT receptor signaling in cultured rat coronary arteries. Cumulative application of 5-HT produced a concentration-dependent vasoconstriction in fresh and 24 h-cultured rat coronary arteries without endothelia. 5-HT induced greater constriction in cultured coronary arteries than in fresh coronary arteries. U46619- and CaCl₂-induced constriction in the two groups was comparable. 5-HT stimulates the 5-HT_2A receptor and cascade of phospholipase C to induce coronary vasoconstriction. Calcium influx through L-type calcium channels and non-L-type calcium channels contributed to the coronary-artery constrictions induced by 5-HT. The contractions mediated by non-L-type calcium channels were significantly enhanced in cultured coronary arteries compared with fresh coronary arteries. The vasoconstriction induced by thapsigargin was also augmented in cultured coronary arteries. The decrease in Orai1 expression significantly inhibited 5-HT-evoked entry of Ca²⁺ in coronary artery cells. Expression of the 5-HT_2A receptor, Orai1 and STIM1 were augmented in cultured coronary arteries compared with fresh coronary arteries.

Conclusions

An increased contraction in response to 5-HT was mediated by the upregulation of 5-HT_2A receptors and downstream signaling in cultured coronary arteries.

Characterization of the contractile P2Y14 receptor in mouse coronary and cerebral arteries

Extracellular UDP-glucose can activate the purinergic P2Y14 receptor. The aim of the present study was to examine the physiological importance of P2Y14 receptors in the vasculature. The data presented herein show that UDP-glucose causes contraction in mouse coronary and basilar arteries. The EC50 values and immunohistochemistry illustrated the strongest P2Y14 receptor expression in the basilar artery. In the presence of pertussis toxin, UDP-glucose inhibited contraction in coronary arteries and in the basilar artery it surprisingly caused relaxation. After organ culture of the coronary artery, the EC50 value decreased and an increased staining for the P2Y14 receptor was observed, showing receptor plasticity.

DMSO-soluble cigarette smoke particles alter the expression of endothelin B receptor in rat coronary artery

In coronary artery diseases, cigarette smoking is a risk factor and the endothelin system plays a key role in the pathogenesis. This study was to examine if dimethylsulfoxide-soluble smoke particles (DSP) upregulate endothelin type-B (ETB) receptors in the coronary artery and investigate the mechanism. The isolated rat coronary arteries were organ-cultured for 24 h. The contractile response of the coronary artery was recorded by myograph. The mRNA and protein expression of the ETB receptors was studied using quantitative real-time PCR and immunohistochemistry. Results showed that the ETB receptor agonist, sarafotoxin 6c, induced a weak contraction in the fresh coronary artery. After culture, the contraction curve mediated by ETB receptor was shifted towards the left with an increased Emax of 152 ± 12%. DSP of 0.2 and 0.4 μl/ml shifted the concentration-contractile curves towards the left with further increased Emax of 270 ± 26 and 280 ± 29%, respectively. The culture increased ETB receptor mRNA and protein levels from fresh arteries, which was further enhanced by DSP. PD98059 (ERK1/2 inhibitor), wedelolactone (NF-κB inhibitor), actinomycin D or cycloheximide significantly inhibited the DSP-enhanced contraction and expression of mRNA and protein of the ETB receptor. However, SB203580 (p38 inhibitor) further increased DSP-enhanced contraction and protein expression of the ETB receptor. The results indicate that DSP upregulates ETB receptors in rat coronary artery via ERK1/2 and the NF-κB pathway.

Vascular endothelin receptor type B: structure, function and dysregulation in vascular disease

Endothelin-1 (ET-1) is a major regulator of vascular function, acting via both endothelin receptor type A (ET(A)R) and type B (ET(B)R). Although the role of ET(A)R in vascular smooth muscle (VSM) contraction has been studied, little is known about ET(B)R. ET(B)R is a G-protein coupled receptor with a molecular mass of ~50 kDa and 442 amino acids arranged in seven transmembrane domains. Alternative splice variants of ET(B)R and heterodimerization and cross-talk with ET(A)R may affect the receptor function. ET(B)R has been identified in numerous blood vessels with substantial effects in the systemic, renal, pulmonary, coronary and cerebral circulation. ET(B)R in the endothelium mediates the release of relaxing factors such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and could also play a role in ET-1 clearance. ET(B)R in VSM mediates increases in [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other pathways of VSM contraction and cell growth. ET-1/ET(A)R signaling has been associated with salt-sensitive hypertension (HTN) and pulmonary arterial hypertension (PAH), and ET(A)R antagonists have shown some benefits in these conditions. In search for other pathogenetic factors and more effective approaches, the role of alterations in endothelial ET(B)R and VSM ET(B)R in vascular dysfunction, and the potential benefits of modulators of ET(B)R in treatment of HTN and PAH are being examined. Combined ET(A)R/ET(B)R antagonists could be more efficacious in the management of conditions involving upregulation of ET(A)R and ET(B)R in VSM. Combined ET(A)R antagonist with ET(B)R agonist may need to be evaluated in conditions associated with decreased endothelial ET(B)R expression/activity.

Organ culture mimics the effects of hypoxia on membrane potential, K(+) channels and vessel tone in pulmonary artery

BACKGROUND AND PURPOSE

Blood vessel culture is gaining interest for use with transfection-based techniques, but alters the contractile properties of the vessels. The present study tested the effects of culture on the intrinsic tone of rat pulmonary arteries (PAs) and examined the function and expression of K(+) channels regulating the resting membrane potential (E(m)) and tone of pulmonary artery smooth muscle cells (PASMCs).

EXPERIMENTAL APPROACH

Rat intrapulmonary arteries were isolated and cultured under standard and modified conditions. Contractile responses of fresh and cultured PA were compared using vessel myograph. Electrophysiology experiments on isolated PASMCs used the patch-clamp technique. K(+) channel expression was quantified using reverse transcription and real-time PCR.

KEY RESULTS

After 4 days in culture vessels contracted to phenylephrine, but relaxation to carbachol was significantly impaired. Contractile responses to 10 mM KCl, 4-aminopyridine and tetraethylammonium increased, and vessels developed an uncharacteristic relaxation response to Ca(2+)-free solution, nifedipine and levcromakalim. PASMCs from cultured vessels were depolarized and K(+) currents reduced, in association with down-regulation of K(v)1.5, K(v)2.1 and TWIK-related acid-sensitive K(+) channel-1 mRNA. These changes were partially reversed by increased oxygenation of the culture medium or removing the endothelium before culture.

CONCLUSIONS AND IMPLICATIONS

Culture of PA for 3-4 days induced loss of functional K(+) channels, depolarization of PASMCs, Ca(2+) influx, intrinsic tone and spontaneous constrictions, similar to the effects of chronic hypoxia. This limits the use of cultured vessels for studying excitation-contraction coupling, although oxygenating the culture medium and removing the endothelium can help to retain normal smooth muscle function.

Limits of isolation and culture: intact vascular endothelium and BKCa

The potential physiological role of plasmalemmal large-conductance calcium-activated potassium channels (BKCa) in vascular endothelial cells is controversial. Studies of freshly isolated and cultured vascular endothelial cells provide disparate results, both supporting and refuting a role for BKCa in endothelial function. Most studies using freshly isolated, intact, healthy arteries provide little support for a physiological role for BKCa in the endothelium, although recent work suggests that this may not be the case in diseased vessels. In isolated and cultured vascular endothelial cells, the autocrine action of growth factors, hormones, and vasoactive substances results in phenotypic drift. Such an induced heterogeneity is likely a primary factor accounting for the apparent differences, and often enhanced BKCa expression and function, in isolated and cultured vascular endothelial cells. In a similar manner, heterogeneity in endothelial BKCa expression and function in intact arteries may be representative of normal and disease states, BKCa being absent in normal intact artery endothelium and upregulated in disease where dysfunction induces signals that alter channel expression and function. Indeed, in some intact vessels, there is evidence for the presence of BKCa, such as mRNA and/or specific BK subunits, an observation that is consistent with the potential for rapid upregulation, as may occur in disease. This perspective proposes that the disparity in the results obtained for BKCa expression and function from freshly isolated and cultured vascular endothelial cells is largely due to variability in experimental conditions and, furthermore, that the expression of BKCa in intact artery endothelium is primarily associated with disease. Although answers to physiologically relevant questions may only be available in atypical physiological conditions, such as those of isolation and culture, the limitations of these methods require open and objective recognition.

Impairment of coronary endothelial cell ET(B) receptor function after short-term inhalation exposure to whole diesel emissions

Air pollutant levels positively correlate with increases in both acute and chronic cardiovascular disease. The pollutant diesel exhaust (DE) increases endothelin (ET) levels, suggesting that this peptide may contribute to DE-induced cardiovascular disease. We hypothesized that acute exposure to DE also enhances ET-1-mediated coronary artery constrictor sensitivity. Constrictor responses to KCl, U-46619, and ET-1 were recorded by videomicroscopy in pressurized intraseptal coronary arteries from rats exposed for 5 h to DE (300 microg/m(3)) or filtered air (Air). ET-1 constriction was augmented in arteries from DE-exposed rats. Nitric oxide synthase (NOS) inhibition [N(omega)-nitro-L-arginine (L-NNA), 100 microM] and endothelium inactivation augmented ET-1 responses in arteries from Air but not DE rats so that after either treatment responses were not different between groups. DE exposure did not affect KCl and U-46619 constrictor responses, while NOS inhibition augmented KCl constriction equally in both groups. Thus basal NOS activity does not appear to be affected by DE exposure. The endothelin type B (ET(B)) receptor antagonist BQ-788 (10 microM) inhibited ET-1 constriction in DE but not Air arteries, and constriction in the presence of the antagonist was not different between groups. Cytokine levels were not different in plasma from DE and AIR rats, suggesting that acute exposure to DE does not cause an immediate inflammatory response. In summary, a 5-h DE exposure selectively increases constrictor sensitivity to ET-1. This augmentation is endothelium-, NOS-, and ET(B) receptor dependent. These data suggest that DE exposure diminishes ET(B) receptor activation of endothelial NOS and augments ET(B)-dependent vasoconstriction. This augmented coronary vasoreactivity to ET-1 after DE, coupled with previous reports that DE induces production of ET-1, suggests that ET-1 may contribute to the increased incidence of cardiac events during acute increases in air pollution levels.

Methyl (11aS)-1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo-[3',4':1,2]pyridin[3,4-b]indol-2-substituted acetates: synthesis and three-dimensional quantitative structure-activity relationship investigation as a class of novel vasodilators

To find selective inhibitor of phosphodiesterase type 5 (PDE5), the essential structure elements of clinically used drugs sildenafil, vardenafil, and tadalafil were combined and a tetracyclic parent was constructed to which in 2-positions substituted acetic acid methylesters were introduced to form 17 novel vasodilators, methyl (11aS)-1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo[3',4':1,2]- pyridin[3,4-b]indol-2-substituted acetates. By molecular field analysis (MFA), an equation of three-dimensional quantitative structure-activity relationship (3D QSAR) was established, which not only revealed the dependence of the in vitro vasorelaxation activities on the structures but also pointed out the way to design new lead compounds properly. Docking these novel vasodilators into the hydrophobic pocket of phosphodiesterase type 5 (PDE5) revealed that their adaptabilities to this pocket did significantly affect on their vasorelaxation activity. Actually, the docking adaptabilities of these novel vasodilators to PDE5 were consistent with the conformational requirements of them to MFA and with the crystal conformation of two representatives.