Endothelium-derived hyperpolarizing factor mediated relaxations in pig coronary arteries do not involve Gi/o proteins

Altered Vascular Adaptations to Pregnancy in a Rat Model of Advanced Maternal Age

Advanced maternal age (≥35 years old) increases the risk of pregnancy complications such as preeclampsia and fetal growth restriction. We previously demonstrated vascular dysfunction and abnormal pregnancy outcomes in a rat model of advanced maternal age. However, vascular adaptations to pregnancy in aging were not studied. We hypothesize that advanced maternal age is associated with a more vasoconstrictive phenotype due to reduced nitric oxide (NO) and increased activity of matrix metalloproteinases (MMPs), contributing to impaired vascular adaptations to pregnancy. A rat model of advanced maternal age was used: young (4 months) and aged (9.5 months; ∼35 years in humans) non-pregnant and pregnant rats. On gestational day 20 (term = 22 days; non-pregnant rats were aged-matched), blood pressure and heart rate were measured (tail cuff plethysmography) and vascular function was assessed in mesenteric arteries (wire myography). Endothelium-dependent relaxation to methylcholine (MCh) was assessed in the presence/absence of nitric oxide synthase inhibitor (L-NAME), or inhibitors of endothelium-dependent hyperpolarization (EDH; apamin and TRAM-34). Vasoconstriction responses to big endothelin-1 (bigET-1), in the presence/absence of MMPs-inhibitor (GM6001) or endothelin converting enzyme (ECE-1) inhibitor (CGS35066), in addition, ET-1 responsiveness, were measured. Blood pressure was elevated only in aged non-pregnant rats (p < 0.001) compared to all other groups. MCh responses were not different, however, L-NAME decreased maximum vasodilation in young (p < 0.01) and aged pregnant rats (p < 0.001), and decreased MCh sensitivity in young non-pregnant rats (p < 0.01), without effects in aged non-pregnant rats. EDH contribution to relaxation was similar in young non-pregnant, and aged non-pregnant and pregnant rats, while EDH-mediated relaxation was absent in young pregnant rats (p < 0.001). BigET-1 responses were enhanced in aged non-pregnant (p < 0.01) and pregnant rats (p < 0.05). No significant changes in bigET-1 conversion occurred in the presence of MMP-inhibitor, whereas ECE-1 inhibition reduced bigET-1 constriction in aged rats (p < 0.01). No differences in ET-1 sensitivity were observed. In conclusion, contrary to our hypothesis, reduced blood pressure, and an increased EDH-dependent contribution to vasodilation suggest a compensatory mechanism that may reflect beneficial adaptations in these aged rats that were able to maintain pregnancy. These data increase our understanding of how the vascular adaptive pathways in pregnancy compensate for advanced maternal age.

The Novel Inodilator ORM-3819 Relaxes Isolated Porcine Coronary Arteries: Role of Voltage-Gated Potassium Channel Activation

Relaxation and changes in the transmembrane potential of vascular smooth muscle induced by ORM-3819, a novel inodilating compound, were investigated in isolated porcine coronary arteries. Isometric tone was studied on arterial rings precontracted by KCl (30 mM), and resting membrane potential was investigated by a conventional microelectrode technique. ORM-3819 in the concentration range 0.38-230.6 µM evoked concentration-dependent relaxation with a maximum value of 58.1% and an effective concentration of the relaxing substance that caused 50% of maximum relaxation of 72.2 µM. The maximum hyperpolarization produced by ORM-3819 at a concentration of 120 µM (-2.6 ± 0.81 mV, N = 10) did not differ significantly from that induced by C-type natriuretic peptide (CNP), an endogenous hyperpolarizing mediator, at a concentration of 1.4 µM (-3.6 ± 0.38 mV, N = 17). The same effect elicited by the known inodilator levosimendan was less pronounced at a concentration of 3.7 µM: -1.82 ± 0.44 mV, N = 22 (P < 0.05 vs. CNP). The voltage-gated potassium channel inhibitor 4-aminopyridine, at a concentration of 5 mM, attenuated the relaxation induced by ORM-3819 at concentrations of 41.6 or 117.2 µM. These results suggest that ORM-3819 is a potent vasodilating agent able to relieve coronary artery vasospasm by causing hyperpolarization of vascular smooth muscle cells through processes involving activation of voltage-gated potassium channels.

Impaired Coronary Endothelial Vasorelaxation in a Preclinical Model of Peripheral Arterial Insufficiency

The present study was designed to determine whether adult swine with peripheral artery insufficiency (PAI) would exhibit vascular dysfunction in vessels distinct from the affected distal limbs, the coronary conduit arteries. Moreover, we sought to evaluate the effect of exercise training on coronary vasomotor function in PAI. Eighteen female healthy young Yucatan miniature swine were randomly assigned to either occluded exercise trained (Occl-Ex, n=7), or occluded-sedentary (Occl-Sed, n=5), or non-occluded, non-exercised control (Non-Occl-Con, n=6) groups. Occl-Ex pigs were progressively trained by running on a treadmill (5days/week, 12 weeks). The left descending artery (LAD) and left circumflex (LCX) coronary arteries were harvested. Vasorelaxation to adenosine diphosphate (ADP), bradykinin (BK), and sodium nitro-prusside (SNP) were assessed in LAD’s; while constrictor responses to phenylephrine (PE), angiotensin II (Ang II), and endothelin-1 (ET-1) were assessed in LCX’s. Vasorelaxation to ADP was reduced in LADs from Occl-Sed and Occl-Ex pigs (P<0.001) as compared to Non-Occl-Con pigs; however, Occl-Ex pigs exhibited partial recovery (P<0.001) intermediate to the other two groups. BK induced relaxation was reduced in LADs from Occl-Ex and Occl-Sed pigs (P<0.001), compared to Non-Occl-Con, and exercise modestly increased responses to BK (P<0.05). In addition, SNP, PE, Ang II, and ET-1 responses were not significantly different among the groups. Our results indicate that ‘simple’ occlusion of the femoral arteries induces vascular dysfunction in conduit vessels distinct from the affected hindlimbs, as evident in blunted coronary vasorelaxation responses to ADP and BK. These findings imply that PAI, even in the absence of frank atherogenic vascular disease, contributes to vascular dysfunction in the coronary arteries that could exacerbate disease outcome in patients with peripheral artery disease. Further, regular daily physical activity partially recovered the deficit observed in the coronary arteries.

Kaempferol enhances endothelium-dependent relaxation in the porcine coronary artery through activation of large-conductance Ca(2+) -activated K(+) channels

BACKGROUND AND PURPOSE

Kaempferol, a plant flavonoid present in normal human diet, can modulate vasomotor tone. The present study aimed to elucidate the signalling pathway through which this flavonoid enhanced relaxation of vascular smooth muscle.

EXPERIMENTAL APPROACH

The effect of kaempferol on the relaxation of porcine coronary arteries to endothelium-dependent (bradykinin) and -independent (sodium nitroprusside) relaxing agents was studied in an in vitro organ chamber setup. The whole-cell patch-clamp technique was used to determine the effect of kaempferol on potassium channels in porcine coronary artery smooth muscle cells (PCASMCs).

KEY RESULTS

At a concentration without direct effect on vascular tone, kaempferol (3 × 10(-6) M) enhanced relaxations produced by bradykinin and sodium nitroprusside. The potentiation by kaempferol of the bradykinin-induced relaxation was not affected by N(ω)-nitro-L-arginine methyl ester, an inhibitor of NO synthase (10(-4) M) or TRAM-34 plus UCL 1684, inhibitors of intermediate- and small-conductance calcium-activated potassium channels, respectively (10(-6) M each), but was abolished by tetraethylammonium chloride, a non-selective inhibitor of calcium-activated potassium channels (10(-3) M), and iberiotoxin, a selective inhibitor of large-conductance calcium-activated potassium channel (KCa 1.1; 10(-7) M). Iberiotoxin also inhibited the potentiation by kaempferol of sodium nitroprusside-induced relaxations. Kaempferol stimulated an outward-rectifying current in PCASMCs, which was abolished by iberiotoxin.

CONCLUSIONS AND IMPLICATIONS

The present results suggest that, in smooth muscle cells of the porcine coronary artery, kaempferol enhanced relaxations caused by endothelium-derived and exogenous NO as well as those due to endothelium-dependent hyperpolarization. This vascular effect of kaempferol involved the activation of KCa 1.1 channels.

Type 2 Diabetes: Endothelial dysfunction and Exercise

PURPOSE

Vascular endothelial dysfunction is an early marker of atherosclerosis characterized by decreased nitric oxide bioavailability in the vascular endothelium and smooth muscle cells. Recently, some animal models and in vitro trials demonstrated that excessive superoxide production from mitochondria within vascular endothelial cells played a role in the pathogenesis of atherosclerosis in type 2 diabetes. This review provides a systematic assessment of the effectiveness of exercise to identify effective approaches to recognize diabetes risk and prevent progression to heart disease.

METHODS

A systematic literature search was conducted to retrieve articles from 1979 to 2013 using the following databases: the MEDLINE, PubMed. Articles had to describe an intervention that physical activity and exercise to identify effective approaches to heart and vascular endothelium.

RESULTS

Currently, physical activity and exercise guidelines aimed to improve cardiovascular health in patients with type 2 diabetes are nonspecific. Benefit of aerobic exercise training on vascular endothelial function in type 2 diabetic patients is still controversial.

CONCLUSION

it is necessary to demonstrate the mechanism of endothelial dysfunction from live human tissues so that we can provide more specific exercise training regimens to enhance cardiovascular health in type 2 diabetic patients.

New positive Ca2+-activated K+ channel gating modulators with selectivity for KCa3.1

Small-conductance (KCa2) and intermediate-conductance (KCa3.1) calcium-activated K(+) channels are voltage-independent and share a common calcium/calmodulin-mediated gating mechanism. Existing positive gating modulators like EBIO, NS309, or SKA-31 activate both KCa2 and KCa3.1 channels with similar potency or, as in the case of CyPPA and NS13001, selectively activate KCa2.2 and KCa2.3 channels. We performed a structure-activity relationship (SAR) study with the aim of optimizing the benzothiazole pharmacophore of SKA-31 toward KCa3.1 selectivity. We identified SKA-111 (5-methylnaphtho[1,2-d]thiazol-2-amine), which displays 123-fold selectivity for KCa3.1 (EC50 111 ± 27 nM) over KCa2.3 (EC50 13.7 ± 6.9 μM), and SKA-121 (5-methylnaphtho[2,1-d]oxazol-2-amine), which displays 41-fold selectivity for KCa3.1 (EC50 109 nM ± 14 nM) over KCa2.3 (EC50 4.4 ± 1.6 μM). Both compounds are 200- to 400-fold selective over representative KV (KV1.3, KV2.1, KV3.1, and KV11.1), NaV (NaV1.2, NaV1.4, NaV1.5, and NaV1.7), as well as CaV1.2 channels. SKA-121 is a typical positive-gating modulator and shifts the calcium-concentration response curve of KCa3.1 to the left. In blood pressure telemetry experiments, SKA-121 (100 mg/kg i.p.) significantly lowered mean arterial blood pressure in normotensive and hypertensive wild-type but not in KCa3.1(-/-) mice. SKA-111, which was found in pharmacokinetic experiments to have a much longer half-life and to be much more brain penetrant than SKA-121, not only lowered blood pressure but also drastically reduced heart rate, presumably through cardiac and neuronal KCa2 activation when dosed at 100 mg/kg. In conclusion, with SKA-121, we generated a KCa3.1-specific positive gating modulator suitable for further exploring the therapeutical potential of KCa3.1 activation.

A-FABP and oxidative stress underlie the impairment of endothelium-dependent relaxations to serotonin and the intima-medial thickening in the porcine coronary artery with regenerated endothelium

Experiments were designed to determine the cause of the selective dysfunction of G(i) proteins, characterized by a reduced endothelium-dependent relaxation to serotonin (5-hydroxytryptamine), in coronary arteries lined with regenerated endothelial cells. Part of the endothelium of the left anterior descending coronary artery of female pigs was removed in vivo to induce regeneration. The animals were treated chronically with vehicle (control), apocynin (antioxidant), or BMS309403 (A-FABP inhibitor) for 28 days before functional examination and histological analysis of segments of coronary arteries with native or regenerated endothelium of the same hearts. Isometric tension was recorded in organ chambers and cumulative concentration-relaxation curves obtained in response to endothelium-dependent [serotonin (G(i) protein mediated activation of eNOS) and bradykinin (G(q) protein mediated activation of eNOS)] and independent [detaNONOate (cGMP-mediated), isoproterenol (cAMP-mediated)] vasodilators. The two inhibitors tested did not acutely affect relaxations of preparations with either native or regenerated endothelium. In the chronically treated groups, however, both apocynin and BMS309403 abolished the reduction in relaxation to serotonin in segments covered with regenerated endothelium and prevented the intima-medial thickening caused by endothelial regeneration, without affecting responses to bradykinin or endothelium-independent agonists (detaNONOate and isoproterenol). Thus, inhibition of either oxidative stress or A-FABP likely prevents both the selective dysfunction of G(i) protein mediated relaxation to serotonin and the neointimal thickening resulting from endothelial regeneration.

Regulator of G protein signaling 2 deficiency causes endothelial dysfunction and impaired endothelium-derived hyperpolarizing factor-mediated relaxation by dysregulating Gi/o signaling

Regulator of G protein signaling 2 (RGS2) is a GTPase-activating protein for G(q/11)α and G(i/o)α subunits. RGS2 deficiency is linked to hypertension in mice and humans, although causative mechanisms are not understood. Because endothelial dysfunction and increased peripheral resistance are hallmarks of hypertension, determining whether RGS2 regulates microvascular reactivity may reveal mechanisms relevant to cardiovascular disease. Here we have determined the effects of systemic versus endothelium- or vascular smooth muscle-specific deletion of RGS2 on microvascular contraction and relaxation. Contraction and relaxation of mesenteric resistance arteries were analyzed in response to phenylephrine, sodium nitroprusside, or acetylcholine with or without inhibitors of nitric oxide (NO) synthase or K(+) channels that mediate endothelium-derived hyperpolarizing factor (EDHF)-dependent relaxation. The results showed that deleting RGS2 in vascular smooth muscle had minor effects. Systemic or endothelium-specific deletion of RGS2 strikingly inhibited acetylcholine-evoked relaxation. Endothelium-specific deletion of RGS2 had little effect on NO-dependent relaxation but markedly impaired EDHF-dependent relaxation. Acute, inducible deletion of RGS2 in endothelium did not affect blood pressure significantly. Impaired EDHF-mediated vasodilatation was rescued by blocking G(i/o)α activation with pertussis toxin. These findings indicated that systemic or endothelium-specific RGS2 deficiency causes endothelial dysfunction resulting in impaired EDHF-dependent vasodilatation. RGS2 deficiency enables endothelial G(i/o) activity to inhibit EDHF-dependent relaxation, whereas RGS2 sufficiency facilitates EDHF-evoked relaxation by squelching endothelial G(i/o) activity. Mutation or down-regulation of RGS2 in hypertension patients therefore may contribute to endothelial dysfunction and defective EDHF-dependent relaxation. Blunting G(i/o) signaling might improve endothelial function in such patients.

Endothelium-dependent nitric oxide and hyperpolarization-mediated venous relaxation pathways in rat inferior vena cava

INTRODUCTION

The vascular endothelium plays a major role in the control of arterial tone; however, its role in venous tissues is less clear. The purpose of this study was to determine the role of endothelium in the control of venous function and the relaxation pathways involved.

METHODS

Circular segments of inferior vena cava (IVC) from male Sprague-Dawley rats were suspended between two wires and isometric contraction to phenylephrine (Phe; 10(-5)M) and 96 mM KCl was measured. Acetylcholine (Ach; 10(-10) to 10(-5)M) was added and the percentage of venous relaxation was measured. To determine the role of nitric oxide (NO) and prostacyclin (PGI(2)), vein relaxation was measured in the presence of the nitric oxide synthase inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME; 3 × 10(-4) M) and the cyclooxygenase inhibitor indomethacin (10(-5) M). To measure the role of hyperpolarization, vein relaxation was measured in the presence of K(+) channel activator cromakalim (10(-11) to 10(-6) M), and the nonselective K(+) channel blocker tetraethylammonium (TEA; 10(-3) M). To test for the contribution of a specific K(+) channel, the effects of K(+) channel blockers: glibenclamide (adenosine triphosphate [ATP]-sensitive K(ATP), 10(-5) M), 4-aminopyridine (4-AP; voltage-dependent K(v), 10(-3) M), apamin (small conductance Ca(2+)-dependent SK(Ca), 10(-7) M), and iberiotoxin (large conductance Ca(2+)-dependent BK(Ca), 10(-8) M) on Ach-induced relaxation were tested.

RESULTS

Ach caused concentration-dependent relaxation of Phe contraction (maximum 49.9 ± 4.9%). Removal of endothelium abolished Ach-induced relaxation. IVC treatment with L-NAME partially reduced Ach relaxation (32.8 ± 4.9%). In IVC treated with L-NAME plus indomethacin, significant Ach-induced relaxation (33.6 ± 3.2%) could still be observed, suggesting a role of endothelium-derived hyperpolarizing factor (EDHF). In IVC treated with L-NAME, indomethacin and TEA, Ach relaxation was abolished, supporting a role of EDHF. In veins stimulated with high KCl, Ach caused relaxation (maximum 59.5 ± 3.5%) that was abolished in the presence of L-NAME and indomethacin suggesting that any Ach-induced EDHF is blocked in the presence of high KCl depolarizing solution, which does not favor outward movement of K(+) ion and membrane hyperpolarization. Cromakalim, an activator of K(ATP), caused significant IVC relaxation when applied alone or on top of maximal Ach-induced relaxation, suggesting that the Ach response may not involve K(ATP). Ach-induced relaxation was not inhibited by glibenclamide, 4-AP, or apamin, suggesting little role of K(ATP), K(v) or SK(Ca), respectively. In contrast, iberiotoxin significantly inhibited Ach-induced relaxation, suggesting a role of BK(Ca).

CONCLUSIONS

Thus, endothelium-dependent venous relaxation plays a major role in the control of venous function. In addition to NO, an EDHF pathway involving BK(Ca) may play a role in endothelium-dependent venous relaxation.

Potentiation of EDHF-mediated relaxation by chloride channel blockers

AIM

To investigate the involvement of Cl⁻ channels in endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation in rat mesenteric arteries.

METHODS

Cl⁻ channel and K(ir) channel activities were studied using whole-cell patch clamping in rat mesenteric arterial smooth muscle cells. Isometric tension of arterial rings was measured in organ chambers.

RESULTS

The volume-activated Cl⁻ current in rat mesenteric arterial smooth muscle cells was abolished by Cl⁻ channel blockers NPPB or DIDS. The EDHF-mediated vasorelaxation was potentiated by NPPB and DIDS. The EDHF response was diminished by a combination of apamin and charybdotoxin, which agreed with the hypothesis that EDHF response involves the release of K(+) via the Ca²(+)-activated K(+) channels in endothelial cells. The elevation of K(+) concentration in bathing solution from 1.2 mmol/L to 11.2 mmol/L induced an arterial relaxation, which was abolished by the combination of BaCl₂ and ouabain. It is consistent to the hypothesis that K(+) activates K(+)/Na(+)-ATPase and inward rectifier K(+) (K(ir)) channels, leading to the hyperpolarization and relaxation of vascular smooth muscle. The K(+)-induced relaxation was augmented by NPPB, DIDS, or withdrawal of Cl⁻ from the bathing solution, which could be reversed by BaCl₂, but not ouabain. The potentiating effect of Cl⁻ channel blockers on K(+)-induced relaxation was probably due to the interaction between Cl⁻ channels and K(ir) channels. Moreover, the K(+)-induced relaxation was potentiated when the arteries were incubated in hyperosmotic solution, which is known to inhibit volume-activated Cl⁻ channels.

CONCLUSION

The inhibition of Cl⁻ channels, particularly the volume-activated Cl⁻ channels, may potentiate the EDHF-induced vasorelaxation through the K(ir) channels.