Regulation of NO-dependent acetylcholine relaxation by K+ channels and the Na+-K+ ATPase pump in porcine internal mammary artery

Effect of D4 Dopamine Receptor on Na+-K+-ATPase Activity in Renal Proximal Tubule Cells

Dopamine, via its receptors, plays a vital role in the maintenance of blood pressure by modulating renal sodium transport. However, the role of the D₄ dopamine receptor (D₄ receptor) in renal proximal tubules (PRTs) is still unclear. This study aimed to verify the hypothesis that activation of D₄ receptor directly inhibits the activity of the Na⁺-K⁺-ATPase (NKA) in RPT cells.

Methods

NKA activity, nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) levels were measured in RPT cells treated with the D₄ receptor agonist PD168077 and/or the D₄ receptor antagonist L745870, the NO synthase inhibitor NG-nitro-L-arginine-methyl ester (L-NAME) or the soluble guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo-[4,3-a] quinoxalin-1-one (ODQ). Total D₄ receptor expression and its expression in the plasma membrane were investigated by immunoblotting in RPT cells from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs).

Results

Activation of D₄ receptors with PD168077, inhibited NKA activity in RPT cells from WKY rats in a concentration- and time-dependent manner. The inhibitory effect of PD168077 on NKA activity was prevented by the addition of the D₄ receptor antagonist L745870, which by itself had no effect. The NO synthase inhibitor L-NAME and the soluble guanylyl cyclase inhibitor ODQ, which by themselves had no effect on NKA activity, eliminated the inhibitory effect of PD168077 on NKA activity. Activation of D₄ receptors also increased NO levels in the culture medium and cGMP levels in RPT cells. However, the inhibitory effect of D₄ receptors on NKA activity was absent in RPT cells from SHRs, which could be related to decreased plasma membrane expression of D₄ receptors in SHR RPT cells.

Conclusions

Activation of D₄ receptors directly inhibits NKA activity via the NO/cGMP signaling pathway in RPT cells from WKY rats but not SHRs. Aberrant regulation of NKA activity in RPT cells may be involved in the pathogenesis of hypertension.

Na+-K+-ATPase plays a major role in mediating cutaneous thermal hyperemia achieved by local skin heating to 39°C

Na⁺-K⁺-ATPase is integrally involved in mediating cutaneous vasodilation during an exercise-heat stress, which includes an interactive role with nitric oxide synthase (NOS). Here, we assessed if Na⁺-K⁺-ATPase also contributes to cutaneous thermal hyperemia induced by local skin heating, which is commonly used to assess cutaneous endothelium-dependent vasodilation. Furthermore, we assessed the extent to which NOS contributes to this response. Cutaneous vascular conductance (CVC) was measured continuously at four forearm skin sites in 11 young adults (4 women). After baseline measurement, local skin temperature was increased from 33°C to 39°C to induce cutaneous thermal hyperemia. Once a plateau in CVC was achieved, each skin site was continuously perfused via intradermal microdialysis with either: 1) lactated Ringer solution (control), 2) 6 mM ouabain, a Na⁺-K⁺-ATPase inhibitor, 3) 20 mM l-NAME, a NOS inhibitor, or 4) a combination of both. Relative to the control site, CVC during the plateau phase of cutaneous thermal hyperemia (∼50% max) was reduced by the lone inhibition of Na⁺-K⁺-ATPase (-19 ± 8% max, P = 0.038) and NOS (-32 ± 4% max, P < 0.001), as well as the combined inhibition of both (-37 ± 9% max, P < 0.001). The magnitude of reduction was similar between NOS inhibition alone and combined inhibition (P = 1.000). The administration of both Na⁺-K⁺-ATPase and NOS inhibitors fully abolished the plateau of CVC with values returning to preheating baseline values (P = 0.439). We show that Na⁺-K⁺-ATPase contributes to cutaneous thermal hyperemia during local skin heating to 39°C, and this response is partially mediated by NOS.NEW & NOTEWORTHY Cutaneous thermal hyperemia during local skin heating to 39°C, which is highly dependent on nitric oxide synthase (NOS), is frequently used to assess endothelium-dependent cutaneous vasodilation. We showed that Na⁺-K⁺-ATPase mediates the regulation of cutaneous thermal hyperemia partly via NOS-dependent mechanisms although a component of the Na⁺-K⁺-ATPase modulation of cutaneous thermal hyperemia is NOS independent. Thus, as with NOS, Na⁺-K⁺-ATPase may be important in the regulation of cutaneous endothelial vascular function.

Phospholemman Phosphorylation Regulates Vascular Tone, Blood Pressure, and Hypertension in Mice and Humans

BACKGROUND

Although it has long been recognized that smooth muscle Na/K ATPase modulates vascular tone and blood pressure (BP), the role of its accessory protein phospholemman has not been characterized. The aim of this study was to test the hypothesis that phospholemman phosphorylation regulates vascular tone in vitro and that this mechanism plays an important role in modulation of vascular function and BP in experimental models in vivo and in humans.

METHODS

In mouse studies, phospholemman knock-in mice (PLM3SA; phospholemman [FXYD1] in which the 3 phosphorylation sites on serines 63, 68, and 69 are mutated to alanines), in which phospholemman is rendered unphosphorylatable, were used to assess the role of phospholemman phosphorylation in vitro in aortic and mesenteric vessels using wire myography and membrane potential measurements. In vivo BP and regional blood flow were assessed using Doppler flow and telemetry in young (14-16 weeks) and old (57-60 weeks) wild-type and transgenic mice. In human studies, we searched human genomic databases for mutations in phospholemman in the region of the phosphorylation sites and performed analyses within 2 human data cohorts (UK Biobank and GoDARTS [Genetics of Diabetes Audit and Research in Tayside]) to assess the impact of an identified single nucleotide polymorphism on BP. This single nucleotide polymorphism was expressed in human embryonic kidney cells, and its effect on phospholemman phosphorylation was determined using Western blotting.

RESULTS

Phospholemman phosphorylation at Ser63 and Ser68 limited vascular constriction in response to phenylephrine. This effect was blocked by ouabain. Prevention of phospholemman phosphorylation in the PLM3SA mouse profoundly enhanced vascular responses to phenylephrine both in vitro and in vivo. In aging wild-type mice, phospholemman was hypophosphorylated, and this correlated with the development of aging-induced essential hypertension. In humans, we identified a nonsynonymous coding variant, single nucleotide polymorphism rs61753924, which causes the substitution R70C in phospholemman. In human embryonic kidney cells, the R70C mutation prevented phospholemman phosphorylation at Ser68. This variant's rare allele is significantly associated with increased BP in middle-aged men.

CONCLUSIONS

These studies demonstrate the importance of phospholemman phosphorylation in the regulation of vascular tone and BP and suggest a novel mechanism, and therapeutic target, for aging-induced essential hypertension in humans.

NO-induced vasodilation correlates directly with BP in smooth muscle-Na/Ca exchanger-1-engineered mice: elevated BP does not attenuate endothelial function

Arterial smooth muscle Na+/Ca2+ exchanger-1 (SM-NCX1) promotes vasoconstriction or vasodilation by mediating, respectively, Ca2+ influx or efflux. In vivo, SM-NCX1 mediates net Ca2+ influx to help maintain myogenic tone (MT) and neuronally activated constriction. SM-NCX1-TG (overexpressing transgenic) mice have increased MT and mean blood pressure (MBP; +13.5 mmHg); SM-NCX1-KO (knockout) mice have reduced MT and MBP (-11.1 mmHg). Endothelium-dependent vasodilation (EDV) is often impaired in hypertension. We tested whether genetically engineered SM-NCX1 expression and consequent BP changes similarly alter EDV. Isolated, pressurized mesenteric resistance arteries with MT from SM-NCX1-TG and conditional SM-NCX1-KO mice, and femoral arteries in vivo from TG mice were studied. Acetylcholine (ACh)-dilated TG arteries with MT slightly more than control or KO arteries, implying that SM-NCX1 overexpression does not impair EDV. In preconstricted KO, but not TG mouse arteries, however, ACh- and bradykinin-triggered vasodilation was markedly attenuated. To circumvent the endothelium, phenylephrine-constricted resistance arteries were tested with Na-nitroprusside [SNP; nitric oxide (NO) donor] and cGMP. This endothelium-independent vasodilation was augmented in TG but attenuated in KO arteries that lack NCX1-mediated Ca2+ clearance. Baseline cytosolic Ca2+ ([Ca2+]cyt) was elevated in TG femoral arteries in vivo, supporting the high BP; furthermore, SNP-triggered [Ca2+]cyt decline and vasodilation were augmented as NO and cGMP promote myocyte polarization thereby enhancing NCX1-mediated Ca2+ efflux. The TG mouse data indicate that BP elevation does not attenuate endothelium-dependent vasodilation. Thus, in essential hypertension and many models the endothelial impairment that supports the hypertension apparently is not triggered by BP elevation but by extravascular mechanisms.NEW & NOTEWORTHY Endothelium-dependent, ACh-induced vasodilation (EDV) is attenuated, and arterial myocyte Na+/Ca2+ exchangers (NCX1) are upregulated in many forms of hypertension. Surprisingly, mildly hypertensive smooth muscle-specific (SM)-NCX1 transgenic mice exhibited modestly enhanced EDV and augmented endothelium-independent vasodilation (EIV). Conversely, mildly hypotensive SM-NCX1-knockout mice had greatly attenuated EIV. These adaptations help compensate for NCX1 expression-induced alterations in cytosolic Ca2+ and blood pressure (BP) and belie the view that elevated BP, itself, causes the endothelial dysregulation in hypertension.

Overview of Antagonists Used for Determining the Mechanisms of Action Employed by Potential Vasodilators with Their Suggested Signaling Pathways

This paper is a review on the types of antagonists and the signaling mechanism pathways that have been used to determine the mechanisms of action employed for vasodilation by test compounds. Thus, we exhaustively reviewed and analyzed reports related to this topic published in PubMed between the years of 2010 till 2015. The aim of this paperis to suggest the most appropriate type of antagonists that correspond to receptors that would be involved during the mechanistic studies, as well as the latest signaling pathways trends that are being studied in order to determine the route(s) that atest compound employs for inducing vasodilation. The methods to perform the mechanism studies were included. Fundamentally, the affinity, specificity and selectivity of the antagonists to their receptors or enzymes were clearly elaborated as well as the solubility and reversibility. All the signaling pathways on the mechanisms of action involved in the vascular tone regulation have been well described in previous review articles. However, the most appropriate antagonists that should be utilized have never been suggested and elaborated before, hence the reason for this review.

The interactive contributions of Na(+) /K(+) -ATPase and nitric oxide synthase to sweating and cutaneous vasodilatation during exercise in the heat

KEY POINTS

Nitric oxide synthase (NOS) contributes to sweating and cutaneous vasodilatation during exercise in the heat. Similarly, reports show that Na(+) /K(+) -ATPase activation can modulate sweating and microvascular circulation. In light of the fact that NO can activate Na(+) /K(+) -ATPase, we evaluated whether there is an interaction between Na(+) /K(+) -ATPase and NOS in the regulation of heat loss responses during an exercise-induced heat stress. We demonstrate that Na(+) /K(+) -ATPase and NOS do not synergistically influence local forearm sweating during moderate intensity (fixed rate of metabolic heat production of 500 W) exercise in the heat (35°C). Conversely, we show an interactive role between NOS and Na(+) /K(+) -ATPase in the modulation of cutaneous vasodilatation. These findings provide novel insight regarding the mechanisms underpinning the control of sweating and cutaneous vasodilatation during exercise in the heat. Given that ouabain may be prescribed as a cardiac glycoside in clinical settings, potential heat loss impairments with ouabain administration should be explored.

ABSTRACT

Nitric oxide (NO) synthase (NOS) contributes to the heat loss responses of sweating and cutaneous vasodilatation. Given that NO can activate Na(+) /K(+) -ATPase, which also contributes to sweating and microvasculature regulation, we evaluated the separate and combined influence of Na(+) /K(+) -ATPase and NOS on sweating and cutaneous vasodilatation. Thirteen young (23±3 years) males performed two 30 min semi-recumbent cycling bouts in the heat (35°C) at a fixed rate of metabolic heat production (500 W) followed by 20 and 40 min recoveries, respectively. Local sweat rate (LSR) and cutaneous vascular conductance (CVC) were measured at four forearm skin sites continuously perfused via intradermal microdialysis with either: (1) lactated Ringer solution (Control); (2) 6 mᴍ ouabain (Ouabain), a Na(+) /K(+) -ATPase inhibitor; (3) 10 mᴍ l-N(G) -nitroarginine methyl ester (l-NAME), a NOS inhibitor; or (4) 6 mᴍ ouabain and 10 mᴍ l-NAME (Ouabain+l-NAME). At the end of both exercise bouts relative to Control, LSR was attenuated with Ouabain (54-60%), l-NAME (12-13%) and Ouabain+l-NAME (68-74%; all P < 0.05). Moreover, the sum of attenuations from Control induced by independent administration of Ouabain and l-NAME was similar to the combined infusion of Ouabain+l-NAME (both P ≥ 0.74). Compared to Control, CVC at the end of both exercise bouts was similar with Ouabain (both P ≥ 0.30), but attenuated with l-NAME (%CVCmax reduction from Control, 24-25%). Furthermore, CVC at the Ouabain+l-NAME site (38-39%; all P < 0.01) was attenuated compared to Control and did not differ from baseline resting values (both P ≥ 0.81). We show that Na(+) /K(+) -ATPase and NOS do not synergistically mediate sweating, whereas they influence cutaneous blood flow in an interactive manner during exercise in the heat.

Evidence for cyclooxygenase-dependent sweating in young males during intermittent exercise in the heat

Our recent work implicated nitric oxide (NO) in the control of sweating during intermittent exercise; however, it is unclear if cyclooxygenase (COX) is also involved. On separate days, ten healthy young (24 ± 4 years) males cycled in the heat (35°C). Two 30 min exercise bouts were performed at either a moderate (400 W, moderate heat load) or high (700 W, high heat load) rate of metabolic heat production and were followed by 20 and 40 min of recovery, respectively. Forearm sweating (ventilated capsule) was evaluated at four skin sites that were continuously perfused via intradermal microdialysis with: (1) lactated Ringer solution (Control), (2) 10 mm ketorolac (a non-selective COX inhibitor), (3) 10 mm N G-nitro-l -arginine methyl ester (l -NAME; a non-selective NO synthase inhibitor) or (4) a combination of 10 mm ketorolac + 10 mm l -NAME. During the last 5 min of the first exercise at moderate heat load, forearm sweating (mg min−1 cm−2) was equivalently reduced with ketorolac (0.54 ± 0.08), l -NAME (0.55 ± 0.07) and ketorolac+l -NAME (0.56 ± 0.08) compared to Control (0.67 ± 0.06) (all P  < 0.05). Similar results were obtained for the second exercise at moderate heat load (all P  < 0.05). However, forearm sweating was similar between the four sites during exercise at high heat load and during recovery regardless of exercise intensity (all P  > 0.05). We show that (1) although both COX and NO modulate forearm sweating during intermittent exercise bouts in the heat at a moderate heat load, the effects are not additive, and (2) the contribution of both enzymes to forearm sweating is less evident during intermittent exercise when the heat load is high and during recovery.

Resistance exercise acutely enhances mesenteric artery insulin-induced relaxation in healthy rats

AIMS

We evaluated the mechanisms involved in insulin-induced vasodilatation after acute resistance exercise in healthy rats.

MAIN METHODS

Wistar rats were divided into 3 groups: control (CT), electrically stimulated (ES) and resistance exercise (RE). Immediately after acute RE (15 sets with 10 repetitions at 70% of maximal intensity), the animals were sacrificed and rings of mesenteric artery were mounted in an isometric system. After this, concentration-response curves to insulin were performed in control condition and in the presence of LY294002 (PI3K inhibitor), L-NAME (NOS inhibitor), L-NAME+TEA (K(+) channels inhibitor), LY294002+BQ123 (ET-A antagonist) or ouabain (Na(+)/K(+) ATPase inhibitor).

KEY FINDINGS

Acute RE increased insulin-induced vasorelaxation as compared to control (CT: Rmax=7.3 ± 0.4% and RE: Rmax=15.8 ± 0.8%; p<0.001). NOS inhibition reduced (p<0.001) this vasorelaxation from both groups (CT: Rmax=2.0 ± 0.3%, and RE: Rmax=-1.2 ± 0.1%), while PI3K inhibition abolished the vasorelaxation in CT (Rmax=-0.1±0.3%, p<0.001), and caused vasoconstriction in RE (Rmax=-6.5 ± 0.6%). That insulin-induced vasoconstriction on PI3K inhibition was abolished (p<0.001) by the ET-A antagonist (Rmax=2.9 ± 0.4%). Additionally, acute RE enhanced (p<0.001) the functional activity of the ouabain-sensitive Na(+)/K(+) ATPase activity (Rmax=10.7 ± 0.4%) and of the K(+) channels (Rmax=-6.1±0.5%; p<0.001) in the insulin-induced vasorelaxation as compared to CT.

SIGNIFICANCE

Such results suggest that acute RE promotes enhanced insulin-induced vasodilatation, which could act as a fine tuning to vascular tone.

Cross talk between S-nitrosylation and S-glutathionylation in control of the Na,K-ATPase regulation in hypoxic heart

Oxygen-induced regulation of Na,K-ATPase was studied in rat myocardium. In rat heart, Na,K-ATPase responded to hypoxia with a dose-dependent inhibition in hydrolytic activity. Inhibition of Na,K-ATPase in hypoxic rat heart was associated with decrease in nitric oxide (NO) production and progressive oxidative stress. Accumulation of oxidized glutathione (GSSG) and decrease in NO availability in hypoxic rat heart were followed by a decrease in S-nitrosylation and upregulation of S-glutathionylation of the catalytic α-subunit of the Na,K-ATPase. Induction of S-glutathionylation of the α-subunit by treatment of tissue homogenate with GSSG resulted in complete inhibition of the enzyme in rat a myocardial tissue homogenate. Inhibitory effect of GSSG in rat sarcolemma could be significantly decreased upon activation of NO synthases. We have further tested whether oxidative stress and suppression of the Na,K-ATPase activity are observed in hypoxic heart of two subterranean hypoxia-tolerant blind mole species (Spalax galili and Spalax judaei). In both hypoxia-tolerant Spalax species activity of the enzyme and tissue redox state were maintained under hypoxic conditions. However, localization of cysteines within the catalytic subunit of the Na,K-ATPase was preserved and induction of S-glutathionylation by GSSG in tissue homogenate inhibited the Spalax ATPase as efficiently as in rat heart. The obtained data indicate that oxygen-induced regulation of the Na,K-ATPase in the heart is mediated by a switch between S-glutathionylation and S-nitrosylation of the regulatory thiol groups localized at the catalytic subunit of the enzyme.

Endothelial and neural factors functionally involved in the modulation of noradrenergic vasoconstriction in healthy pig internal mammary artery

The role of endothelial and neural factors as modulators of neurogenic- and noradrenaline-induced vasoconstriction was examined in healthy pig internal mammary artery (IMA). Tetrodotoxin-, guanethidine-sensitive electrical field stimulation (EFS)-, and noradrenaline-elicited contractions were significantly diminished by prazosin (n=8, P<0.001) and less so by rauwolscine, indicating functional α₁- and α₂-adrenoceptor-mediated noradrenergic innervation of the IMA. Endothelium removal reduced neurogenic (n=8, P<0.01) but augmented noradrenaline responses (n=8, P<0.01), suggesting the release of two endothelium-dependent factors with opposite effects. In the presence of endothelium, neurogenic and exogenous noradrenaline vasoconstrictions were enhanced by L-NOArg (n=7, P<0.05 and P<0.01 respectively) and ODQ (n=7, both P<0.05); in denuded arteries, nNOS inhibition with N(ω)-propyl-L-arginine increased neurogenic contraction (n=7, P<0.05). Western blotting indicated the presence of neural and endothelial origin NO (n=6, P<0.001). Tetraethylammonium (n=9, P<0.001), iberiotoxin (n=7, P<0.001) and 4-aminopyridine (n=8, P<0.01) enhanced vasoconstrictions revealing a modulatory role of big conductance Ca²⁺-activated K⁺ (BK(Ca)) and voltage-dependent K⁺ (K(v)) channels in noradrenergic responses. Bosentan pretreatment (n=8, P<0.05) suggested endothelin-1 as the inferred contractile neurogenic endothelial-dependent factor. Indomethacin-induced inhibition involved a muscular prostanoid (n=9, P<0.05), functionally and immunologically localized, and derived from cyclooxygenase (COX)-1 and COX-2, as revealed by Western blots (n=5, P=0.1267). Thus, noradrenergic IMA contractions are controlled by contractile prostanoid activation and endothelin-1 release, and offset by BK(Ca) and K(v) channels and neural and endothelial NO. These results help clarify the mechanisms of vasospasm in IMA, as the preferred vessel for coronary bypass.

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.