Signalling mechanisms in the cardiovascular protective effects of estrogen: With a focus on rapid/membrane signalling

In modern society, cardiovascular disease remains the biggest single threat to life, being responsible for approximately one third of worldwide deaths. Male prevalence is significantly higher than that of women until after menopause, when the prevalence of CVD increases in females until it eventually exceeds that of men. Because of the coincidence of CVD prevalence increasing after menopause, the role of estrogen in the cardiovascular system has been intensively researched during the past two decades in vitro, in vivo and in observational studies. Most of these studies suggested that endogenous estrogen confers cardiovascular protective and anti-inflammatory effects. However, clinical studies of the cardioprotective effects of hormone replacement therapies (HRT) not only failed to produce proof of protective effects, but also revealed the potential harm estrogen could cause. The "critical window of hormone therapy" hypothesis affirms that the moment of its administration is essential for positive treatment outcomes, pre-menopause (3-5 years before menopause) and immediately post menopause being thought to be the most appropriate time for intervention. Since many of the cardioprotective effects of estrogen signaling are mediated by effects on the vasculature, this review aims to discuss the effects of estrogen on vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) with a focus on the role of estrogen receptors (ERα, ERβ and GPER) in triggering the more recently discovered rapid, or membrane delimited (non-genomic), signaling cascades that are vital for regulating vascular tone, preventing hypertension and other cardiovascular diseases.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

Role of reactive oxygen species and sulfide-quinone oxoreductase in hydrogen sulfide-induced contraction of rat pulmonary arteries

Application of H₂S ("sulfide") elicits a complex contraction in rat pulmonary arteries (PAs) comprising a small transient contraction (phase 1; Ph1) followed by relaxation and then a second, larger, and more sustained contraction (phase 2; Ph2). We investigated the mechanisms causing this response using isometric myography in rat second-order PAs, with Na₂S as a sulfide donor. Both phases of contraction to 1,000 μM Na₂S were attenuated by the pan-PKC inhibitor Gö6983 (3 μM) and by 50 μM ryanodine; the Ca²⁺ channel blocker nifedipine (1 μM) was without effect. Ph2 was attenuated by the mitochondrial complex III blocker myxothiazol (1 μM), the NADPH oxidase (NOX) blocker VAS2870 (10 μM), and the antioxidant TEMPOL (3 mM) but was unaffected by the complex I blocker rotenone (1 μM). The bath sulfide concentration, measured using an amperometric sensor, decreased rapidly following Na₂S application, and the peak of Ph2 occurred when this had fallen to ~50 μM. Sulfide caused a transient increase in NAD(P)H autofluorescence, the offset of which coincided with development of the Ph2 contraction. Sulfide also caused a brief mitochondrial hyperpolarization (assessed using tetramethylrhodamine ethyl ester), followed immediately by depolarization and then a second more prolonged hyperpolarization, the onset of which was temporally correlated with the Ph2 contraction. Sulfide application to cultured PA smooth muscle cells increased reactive oxygen species (ROS) production (recorded using L012); this was absent when the mitochondrial flavoprotein sulfide-quinone oxoreductase (SQR) was knocked down using small interfering RNA. We propose that the Ph2 contraction is largely caused by SQR-mediated sulfide metabolism, which, by donating electrons to ubiquinone, increases electron production by complex III and thereby ROS production.

Transforming growth factor-β enhances Rho-kinase activity and contraction in airway smooth muscle via the nucleotide exchange factor ARHGEF1

Key points

Transforming growth‐factor‐β (TGF‐β) and RhoA/Rho‐kinase are independently implicated in the airway hyper‐responsiveness associated with asthma, but how these proteins interact is not fully understood.

We examined the effects of pre‐treatment with TGF‐β on expression and activity of RhoA, Rho‐kinase and ARHGEF1, an activator of RhoA, as well as on bradykinin‐induced contraction, in airway smooth muscle.

TGF‐β enhanced bradykinin‐induced RhoA translocation, Rho‐kinase‐dependent phosphorylation and contraction, but partially suppressed bradykinin‐induced RhoA activity (RhoA‐GTP content).

TGF‐β enhanced the expression of ARHGEF1, while a small interfering RNA against ARHGEF1 and a RhoGEF inhibitor prevented the effects of TGF‐β on RhoA and Rho‐kinase activity and contraction, respectively.

ARHGEF1 expression was also enhanced in airway smooth muscle from asthmatic patients and ovalbumin‐sensitized mice.

ARHGEF1 is a key TGF‐β target gene, an important regulator of Rho‐kinase activity and therefore a potential therapeutic target for the treatment of asthmatic airway hyper‐responsiveness.

Abstract

Transforming growth factor‐β (TGF‐β), RhoA/Rho‐kinase and Src‐family kinases (SrcFK) have independently been implicated in airway hyper‐responsiveness, but how they interact to regulate airway smooth muscle contractility is not fully understood. We found that TGF‐β pre‐treatment enhanced acute contractile responses to bradykinin (BK) in isolated rat bronchioles, and inhibitors of RhoGEFs (Y16) and Rho‐kinase (Y27632), but not the SrcFK inhibitor PP2, prevented this enhancement. In cultured human airway smooth muscle cells (hASMCs), TGF‐β pre‐treatment enhanced the protein expression of the Rho guanine nucleotide exchange factor ARHGEF1, MLC₂₀, MYPT‐1 and the actin‐severing protein cofilin, but not of RhoA, ROCK2 or c‐Src. In hASMCs, acute treatment with BK triggered subcellular translocation of ARHGEF1 and RhoA and enhanced auto‐phosphorylation of SrcFK and phosphorylation of MYPT1 and MLC₂₀, but induced de‐phosphorylation of cofilin. TGF‐β pre‐treatment amplified the effects of BK on RhoA translocation and MYPT1/MLC₂₀ phosphorylation, but suppressed the effects of BK on RhoA‐GTP content, SrcFK auto‐phosphorylation and cofilin de‐phosphorylation. In hASMCs, an ARHGEF1 small interfering RNA suppressed the effects of BK and TGF‐β on RhoA‐GTP content, RhoA translocation and MYPT1 and MLC₂₀ phosphorylation, but minimally influenced the effects of TGF‐β on cofilin expression and phosphorylation. ARHGEF1 expression was also enhanced in ASMCs of asthmatic patients and in lungs of ovalbumin‐sensitized mice. Our data indicate that TGF‐β enhances BK‐induced contraction, RhoA translocation and Rho‐kinase activity in airway smooth muscle largely via ARHGEF1, but independently of SrcFK and total RhoA‐GTP content. A role for smooth muscle ARHGEF1 in asthmatic airway hyper‐responsiveness is worthy of further investigation.

Transforming growth‐factor‐β (TGF‐β) and RhoA/Rho‐kinase are independently implicated in the airway hyper‐responsiveness associated with asthma, but how these proteins interact is not fully understood.

We examined the effects of pre‐treatment with TGF‐β on expression and activity of RhoA, Rho‐kinase and ARHGEF1, an activator of RhoA, as well as on bradykinin‐induced contraction, in airway smooth muscle.

TGF‐β enhanced bradykinin‐induced RhoA translocation, Rho‐kinase‐dependent phosphorylation and contraction, but partially suppressed bradykinin‐induced RhoA activity (RhoA‐GTP content).

TGF‐β enhanced the expression of ARHGEF1, while a small interfering RNA against ARHGEF1 and a RhoGEF inhibitor prevented the effects of TGF‐β on RhoA and Rho‐kinase activity and contraction, respectively.

ARHGEF1 expression was also enhanced in airway smooth muscle from asthmatic patients and ovalbumin‐sensitized mice.

ARHGEF1 is a key TGF‐β target gene, an important regulator of Rho‐kinase activity and therefore a potential therapeutic target for the treatment of asthmatic airway hyper‐responsiveness.

ROS-dependent activation of RhoA/Rho-kinase in pulmonary artery: Role of Src-family kinases and ARHGEF1

The role of reactive oxygen species (ROS) in smooth muscle contraction is poorly understood. We hypothesised that G-protein coupled receptor (GPCR) activation and hypoxia induce Rho-kinase activity and contraction in rat intra-pulmonary artery (IPA) via stimulation of ROS production and subsequent Src-family kinase (SrcFK) activation. The T-type prostanoid receptor agonist U46619 induced ROS production in pulmonary artery smooth muscle cells (PASMC). U46619 also induced c-Src cysteine oxidation, SrcFK auto-phosphorylation, MYPT-1 and MLC₂₀ phosphorylation and contraction in IPA, and all these responses were inhibited by antioxidants (ebselen, Tempol). Contraction and SrcFK/MYPT-1/MLC₂₀ phosphorylations were also inhibited by combined superoxide dismutase and catalase, or by the SrcFK antagonist PP2, while contraction and MYPT-1/MLC₂₀ phosphorylations were inhibited by the Rho guanine nucleotide exchange factor (RhoGEF) inhibitor Y16. H₂O₂ and the superoxide-generating quinoledione LY83583 both induced c-Src oxidation, SrcFK auto-phosphorylation and contraction in IPA. LY83583 and H₂O₂-induced contractions were inhibited by PP2, while LY83583-induced contraction was also inhibited by antioxidants and Y16. SrcFK auto-phosphorylation and MYPT-1/MLC₂₀ phosphorylation was also induced by hypoxia in IPA and this was blocked by mitochondrial inhibitors rotenone and myxothiazol. In live PASMC, sub-cellular translocation of RhoA and the RhoGEF ARHGEF1 was triggered by both U46619 and LY83583 and this translocation was blocked by antioxidants and PP2. RhoA translocation was also inhibited by an ARHGEF1 siRNA. U46619 enhanced ROS-dependent co-immunoprecipitation of ARHGEF1 with c-Src. Our results demonstrate a link between GPCR-induced cytosolic ROS or hypoxia-induced mitochondrial ROS and SrcFK activity, Rho-kinase activity and contraction. ROS and SrcFK activate RhoA via ARHGEF1.

Divergent modulation of Rho-kinase and Ca(2+) influx pathways by Src family kinases and focal adhesion kinase in airway smooth muscle

Background and Purpose

The importance of tyrosine kinases in airway smooth muscle (ASM) contraction is not fully understood. The aim of this study was to investigate the role of Src‐family kinases (SrcFK) and focal adhesion kinase (FAK) in GPCR‐mediated ASM contraction and associated signalling events.

Experimental Approach

Contraction was recorded in intact or α‐toxin permeabilized rat bronchioles. Phosphorylation of SrcFK, FAK, myosin light‐chain‐20 (MLC₂₀) and myosin phosphatase targeting subunit‐1 (MYPT‐1) was evaluated in cultured human ASM cells (hASMC). [Ca²⁺]_i was evaluated in Fura‐2 loaded hASMC. Responses to carbachol (CCh) and bradykinin (BK) and the contribution of SrcFK and FAK to these responses were determined.

Key Results

Contractile responses in intact bronchioles were inhibited by antagonists of SrcFK, FAK and Rho‐kinase, while after α‐toxin permeabilization, they were sensitive to inhibition of SrcFK and Rho‐kinase, but not FAK. CCh and BK increased phosphorylation of MYPT‐1 and MLC₂₀ and auto‐phosphorylation of SrcFK and FAK. MYPT‐1 phosphorylation was sensitive to inhibition of Rho‐kinase and SrcFK, but not FAK. Contraction induced by SR Ca²⁺ depletion and equivalent [Ca²⁺]_i responses in hASMC were sensitive to inhibition of both SrcFK and FAK, while depolarization‐induced contraction was sensitive to FAK inhibition only. SrcFK auto‐phosphorylation was partially FAK‐dependent, while FAK auto‐phosphorylation was SrcFK‐independent.

Conclusions and Implications

SrcFK mediates Ca²⁺‐sensitization in ASM, while SrcFK and FAK together and individually influence multiple Ca²⁺ influx pathways. Tyrosine phosphorylation is therefore a key upstream signalling event in ASM contraction and may be a viable target for modulating ASM tone in respiratory disease.

Sphingosylphosphorylcholine potentiates vasoreactivity and voltage-gated Ca2+ entry via NOX1 and reactive oxygen species

Aims

Sphingosylphosphorylcholine (SPC) elicits vasoconstriction at micromolar concentrations. At lower concentrations (≤1 µmol/L), however, it does not constrict intrapulmonary arteries (IPAs), but strongly potentiates vasoreactivity. Our aim was to determine whether this also occurs in a systemic artery and to delineate the signalling pathway.

Methods and results

Rat mesenteric arteries and IPAs mounted on a myograph were challenged with ∼25 mmol/L [K⁺] to induce a small vasoconstriction. SPC (1 µmol/L) dramatically potentiated this constriction in all arteries by ∼400%. The potentiation was greatly suppressed or abolished by inhibition of phospholipase C (PLC; U73122), PKCε (inhibitory peptide), Src (PP2), and NADPH oxidase (VAS2870), and also by Tempol (superoxide scavenger), but not by inhibition of Rho kinase (Y27632). Potentiation was lost in mesenteric arteries from p47^phox–/–, but not NOX2^−/–, mice. The intracellular superoxide generator LY83583 mimicked the effect of SPC. SPC elevated reactive oxygen species (ROS) in vascular smooth muscle cells, and this was blocked by PP2, VAS2870, and siRNA knockdown of PKCε. SPC (1 µmol/L) significantly reduced the EC₅₀ for U46619-induced vasoconstriction, an action ablated by Tempol. In patch-clamped mesenteric artery cells, SPC (200 nmol/L) enhanced Ba²⁺ current through L-type Ca²⁺ channels, an action abolished by Tempol but mimicked by LY83583.

Conclusion

Our results suggest that low concentrations of SPC activate a PLC-coupled and NOX1-mediated increase in ROS, with consequent enhancement of voltage-gated Ca²⁺ entry and thus vasoreactivity. We speculate that this pathway is not specific for SPC, but may also contribute to vasoconstriction elicited by other G-protein coupled receptor and PLC-coupled agonists.

Control of vascular smooth muscle function by Src-family kinases and reactive oxygen species in health and disease

Reactive oxygen species (ROS) are now recognised as second messenger molecules that regulate cellular function by reversibly oxidising specific amino acid residues of key target proteins. Amongst these are the Src-family kinases (SrcFKs), a multi-functional group of non-receptor tyrosine kinases highly expressed in vascular smooth muscle (VSM). In this review we examine the evidence supporting a role for ROS-induced SrcFK activity in normal VSM contractile function and in vascular remodelling in cardiovascular disease. VSM contractile responses to G-protein-coupled receptor stimulation, as well as hypoxia in pulmonary artery, are shown to be dependent on both ROS and SrcFK activity. Specific phosphorylation targets are identified amongst those that alter intracellular Ca(2+) concentration, including transient receptor potential channels, voltage-gated Ca(2+) channels and various types of K(+) channels, as well as amongst those that regulate actin cytoskeleton dynamics and myosin phosphatase activity, including focal adhesion kinase, protein tyrosine kinase-2, Janus kinase, other focal adhesion-associated proteins, and Rho guanine nucleotide exchange factors. We also examine a growing weight of evidence in favour of a key role for SrcFKs in multiple pro-proliferative and anti-apoptotic signalling pathways relating to oxidative stress and vascular remodelling, with a particular focus on pulmonary hypertension, including growth-factor receptor transactivation and downstream signalling, hypoxia-inducible factors, positive feedback between SrcFK and STAT3 signalling and positive feedback between SrcFK and NADPH oxidase dependent ROS production. We also discuss evidence for and against the potential therapeutic targeting of SrcFKs in the treatment of pulmonary hypertension.

Redox regulation of protein kinases as a modulator of vascular function

Reactive oxygen species (ROS) are continuously generated in vascular tissues by various oxidoreductase enzymes. They contribute to normal cell signaling, and modulate vascular smooth muscle tone and endothelial permeability in response to physiological agonists and to various cellular stresses and environmental factors, such as hypoxia. While concentrations of ROS are normally tightly controlled by cellular redox buffer systems, if produced in excess they may contribute to vascular disease. Protein kinases are essential components of most cell signaling pathways, including those involving ROS. The functioning of several members of this highly diverse group of enzymes, which include receptor and nonreceptor tyrosine kinases, protein kinase C, mitogen-activated kinases, and Rho-kinase, are modified by ROS, either through direct oxidative modification or indirectly through modification of associated proteins such as tyrosine phosphatases and monomeric G proteins. In this review, we discuss the molecular mechanisms of redox modification of these proteins, the downstream pathways affected, the often complex interaction between major kinase pathways, and feedback to ROS production itself. We also discuss complicating factors such as differential actions of superoxide anion and hydrogen peroxide, questions concerning concentration dependence, and the significance of signaling microdomains.

Superoxide differentially controls pulmonary and systemic vascular tone through multiple signalling pathways

Aims

The aim of this study was to determine the relative importance of Ca²⁺ sensitization, ion channels, and intracellular Ca²⁺ ([Ca²⁺]_i) in the mixed constrictor/relaxation actions of superoxide anion on systemic and pulmonary arteries.

Methods and results

Pulmonary and mesenteric arteries were obtained from rat. Superoxide was generated in arteries and cells with 6-anilino-5,8-quinolinequinone (LY83583). Following pre-constriction with U46619, 10 μmol/L LY83583 caused constriction in pulmonary and relaxation in mesenteric arteries. Both constrictor and relaxant actions of LY83583 were inhibited by superoxide dismutase and catalase. LY83583 caused Rho-kinase-dependent constriction in α-toxin-permeabilized pulmonary but not mesenteric arteries. Phosphorylation of myosin phosphatase-targeting subunit-1 (MYPT-1; as determined by western blot), was enhanced by LY83583 in pulmonary artery only. However, in both artery types, changes in tension were closely correlated with changes in phosphorylation of the 20 kDa myosin light chain as well as changes in [Ca²⁺]_i (as measured with Fura PE-3), with LY83583 causing increases in pulmonary and decreases in mesenteric arteries. When U46619 was replaced by 30 mmol/L K⁺, all changes in [Ca²⁺]_i were abolished and LY83583 constricted both artery types. The K_V channel inhibitor 4-aminopyridine abolished the LY83583-induced relaxation in mesenteric artery without affecting constriction in pulmonary artery. However, LY83583 caused a similar hyperpolarizing shift in the steady-state activation of K_V current in isolated smooth muscle cells of both artery types.

Conclusions

Superoxide only causes Rho-kinase-dependent Ca²⁺ sensitization in pulmonary artery, resulting in constriction, and whilst it opens K_V channels in both artery types, this only results in relaxation in mesenteric.

Superoxide constricts rat pulmonary arteries via Rho-kinase-mediated Ca(2+) sensitization

Reactive oxygen species play a key role in vascular disease, pulmonary hypertension, and hypoxic pulmonary vasoconstriction. We investigated contractile responses, intracellular Ca(2+) ([Ca(2+)](i)), Rho-kinase translocation, and phosphorylation of the regulatory subunit of myosin phosphatase (MYPT-1) and of myosin light chain (MLC(20)) in response to LY83583, a generator of superoxide anion, in small intrapulmonary arteries (IPA) of rat. LY83583 caused concentration-dependent constrictions in IPA and greatly enhanced submaximal PGF(2alpha)-mediated preconstriction. In small femoral or mesenteric arteries of rat, LY83583 alone was without effect, but it relaxed a PGF(2)alpha-mediated preconstriction. Constrictions in IPA were inhibited by superoxide dismutase and tempol, but not catalase, and were endothelium and guanylate cyclase independent. Constrictions were also inhibited by the Rho-kinase inhibitor Y27632 and the Src-family kinase inhibitor SU6656. LY83583 did not raise [Ca(2+)](i), but caused a Y27632-sensitive constriction in alpha-toxin-permeabilized IPA. LY83583 triggered translocation of Rho-kinase from the nucleus to the cytosol in pulmonary artery smooth muscle cells and enhanced phosphorylation of MYPT-1 at Thr-855 and of MLC(20) at Ser-19 in IPA. This enhancement was inhibited by superoxide dismutase and abolished by Y27632. Hydrogen peroxide did not activate Rho-kinase. We conclude that in rat small pulmonary artery, superoxide triggers Rho-kinase-mediated Ca(2+) sensitization and vasoconstriction independent of hydrogen peroxide.

Constriction of pulmonary artery by peroxide: role of Ca2+ release and PKC

Reactive oxygen species are implicated in pulmonary hypertension and hypoxic pulmonary vasoconstriction. We examined the effects of low concentrations of peroxide on intrapulmonary arteries (IPA). IPAs from Wistar rats were mounted on a myograph for recording tension and estimating intracellular Ca2+ using Fura-PE3. Ca2+ sensitization was examined in alpha-toxin-permeabilized IPAs, and phosphorylation of MYPT-1 and MLC(20) was assayed by Western blot. Peroxide (30 microM) induced a vasoconstriction with transient and sustained components and equivalent elevations of intracellular Ca2+. The transient constriction was strongly suppressed by indomethacin, the TP-receptor antagonist SQ-29584, and the Rho kinase inhibitor Y-27632, whereas sustained constriction was unaffected. Neither vasoconstriction nor elevation of intracellular Ca2+ was affected by removal of extracellular Ca2+, whereas dantrolene suppressed the former and ryanodine abolished the latter. Peroxide-induced constriction of permeabilized IPAs was unaffected by Y-27632 but abolished by PKC inhibitors; these also suppressed constriction in intact IPAs. Peroxide caused translocation of PKCalpha, but had no significant effect on MYPT-1 or MLC(20) phosphorylation. We conclude that in IPAs peroxide causes transient release of vasoconstrictor prostanoids, but sustained constriction is associated with release of Ca2+ from ryanodine-sensitive stores and a PKC-dependent but Rho kinase- and MLC(20)-independent constrictor mechanism.

Role of src-family kinases in hypoxic vasoconstriction of rat pulmonary artery

Aims

We investigated the role of src-family kinases (srcFKs) in hypoxic pulmonary vasoconstriction (HPV) and how this relates to Rho-kinase-mediated Ca²⁺ sensitization and changes in intracellular Ca²⁺ concentration ([Ca²⁺]_i).

Methods and results

Intra-pulmonary arteries (IPAs) were obtained from male Wistar rats. HPV was induced in myograph-mounted IPAs. Auto-phosphorylation of srcFKs and phosphorylation of the regulatory subunit of myosin phosphatase (MYPT-1) and myosin light-chain (MLC₂₀) in response to hypoxia were determined by western blotting. Translocation of Rho-kinase and effects of siRNA knockdown of src and fyn were examined in cultured pulmonary artery smooth muscle cells (PASMCs). [Ca²⁺]_i was estimated in Fura-PE3-loaded IPA. HPV was inhibited by two blockers of srcFKs, SU6656 and PP2. Hypoxia enhanced phosphorylation of three srcFK proteins at Tyr-416 (60, 59, and 54 kDa, corresponding to src, fyn, and yes, respectively) and enhanced srcFK-dependent tyrosine phosphorylation of multiple target proteins. Hypoxia caused a complex, time-dependent enhancement of MYPT-1 and MLC₂₀ phosphorylation, both in the absence and presence of pre-constriction. The sustained component of this enhancement was blocked by SU6656 and the Rho-kinase inhibitor Y27632. In PASMCs, hypoxia caused translocation of Rho-kinase from the nucleus to the cytoplasm, and this was prevented by anti-src siRNA and to a lesser extent by anti-fyn siRNA. The biphasic increases in [Ca²⁺]_i that accompany HPV were also inhibited by PP2.

Conclusion

Hypoxia activates srcFKs and triggers protein tyrosine phosphorylation in IPA. Hypoxia-mediated Rho-kinase activation, Ca²⁺ sensitization, and [Ca²⁺]_i responses are depressed by srcFK inhibitors and/or siRNA knockdown, suggesting a central role of srcFKs in HPV.

Low concentrations of sphingosylphosphorylcholine enhance pulmonary artery vasoreactivity: the role of protein kinase C delta and Ca2+ entry

Sphingosylphosphorylcholine (SPC) is a powerful vasoconstrictor, but in vitro its EC(50) is approximately 100-fold more than plasma concentrations. We examined whether subcontractile concentrations of SPC (100 nmol/L of SPC, and independent of the endothelium, 2-aminoethoxydiphenylborane-sensitive Ca(2+) entry, and Rho kinase. It was abolished by the phospholipase C inhibitor U73122, the broad spectrum protein kinase C (PKC) inhibitor Ro31-8220, and the PKC delta inhibitor rottlerin, but not by Gö6976, which is ineffective against PKC delta. The potentiation could be attributed to enhancement of Ca(2+) entry. SPC also potentiated the responses to prostaglandin F(2 alpha) and U436619, which activate a 2-aminoethoxydiphenylborane sensitive nonselective cation channel in intrapulmonary arteries. In this case, potentiation was partially inhibited by diltiazem but abolished by 2-aminoethoxydiphenylborane, Ro31-8220, and rottlerin. SPC (1 micromol/L) caused translocation of PKC delta to the perinuclear region and cytoskeleton of cultured intrapulmonary artery smooth muscle cells. We present the novel finding that low, subcontractile concentrations of SPC potentiate Ca(2+) entry in intrapulmonary arteries through both voltage-dependent and independent pathways via a receptor-dependent mechanism involving PKC delta. This has implications for the physiological role of SPC, especially in cardiovascular disease, where SPC is reported to be elevated.

Interaction between src family kinases and rho-kinase in agonist-induced Ca2+-sensitization of rat pulmonary artery

Aims

We investigated the role of src family kinases (srcFK) in agonist-mediated Ca²⁺-sensitization in pulmonary artery and whether this involves interaction with the rho/rho-kinase pathway.

Methods and results

Intra-pulmonary arteries (IPAs) and cultured pulmonary artery smooth muscle cells (PASMC) were obtained from rat. Expression of srcFK was determined at the mRNA and protein levels. Ca²⁺-sensitization was induced by prostaglandin F_2α (PGF_2α) in α-toxin-permeabilized IPAs. Phosphorylation of the regulatory subunit of myosin phosphatase (MYPT-1) and of myosin light-chain-20 (MLC₂₀) and translocation of rho-kinase in response to PGF_2α were also determined. Nine srcFK were expressed at the mRNA level, including src, fyn, and yes, and PGF_2α enhanced phosphorylation of three srcFK proteins at tyr-416. In α-toxin-permeabilized IPAs, PGF_2α enhanced the Ca²⁺-induced contraction (pCa 6.9) approximately three-fold. This enhancement was inhibited by the srcFK blockers SU6656 and PP2 and by the rho-kinase inhibitor Y27632. Y27632, but not SU6656 or PP2, also inhibited the underlying pCa 6.9 contraction. PGF_2α enhanced phosphorylation of MYPT-1 at thr-697 and thr-855 and of MLC₂₀ at ser-19. This enhancement, but not the underlying basal phosphorylation, was inhibited by SU6656. Y27632 suppressed both basal and PGF_2α-mediated phosphorylation. The effects of SU6656 and Y27632, on both contraction and MYPT-1 and MLC₂₀ phosphorylation, were not additive. PGF_2α triggered translocation of rho-kinase in PASMC, and this was inhibited by SU6656.

Conclusions

srcFK are activated by PGF_2α in the rat pulmonary artery and may contribute to Ca²⁺-sensitization and contraction via rho-kinase translocation and phosphorylation of MYPT-1.

Effect of ceramide on the contractility of pregnant rat uterus

Ceramide and other sphingolipid mediators have emerged as a novel class of lipid second messengers in cell signaling. We assessed the effect of C(2)-ceramide (a membrane permeable analog of ceramide) on spontaneous and agonist-induced contractile responses of uterus, isolated from 19-day pregnant rats. Ceramide (3, 10 microM) moderately, but significantly inhibited the amplitude of spontaneous rhythmic contractions. However, a variable effect was seen on agonist-induced contractions. While 5-HT-induced contractions were markedly inhibited at 3 and 10 microM ceramide, oxytocin and carboprost (a PGF(2)alpha analogue)-induced contractions were not affected by the sphingolipid. Ceramide (10 microM) also markedly inhibited CaCl(2)-induced contractions elicited in K(+)-depolarized tissues. Further, in rabbit portal vein myocytes, which display robust L-type calcium channel current, ceramide inhibited the I(Ba) in a dose-dependent manner. Therefore, it is suggested that the inhibitory effect of ceramide on uterine contractility may involve a decrease in the influx of Ca(2+) through voltage-dependent L-type Ca(2+) channels, such that contractile responses that are primarily dependent on extracellular Ca(2+), like rhythmic and serotonin contractions, were inhibited by ceramide. Further study is required to establish the role of endogenous ceramide and other sphingolipids in regulating uterine tone during gestation and at term.

Dietary soy isoflavone induced increases in antioxidant and eNOS gene expression lead to improved endothelial function and reduced blood pressure in vivo

Epidemiological evidence suggests that populations consuming large amounts of soy protein have a reduced incidence of coronary heart disease (1-5). The cardiovascular risks associated with conventional hormone replacement therapy in postmenopausal women (5-7) have precipitated a search for alternative estrogen receptor modulators. Here we report that long-term feeding of rats with a soy protein-rich (SP) diet during gestation and adult life results in decreased oxidative stress, improved endothelial function, and reduced blood pressure in vivo measured by radiotelemetry in aged male offspring. Improved vascular reactivity in animals fed an SP diet was paralleled by increased mitochondrial glutathione and mRNA levels for endothelial nitric oxide synthase (eNOS) and the antioxidant enzymes manganese superoxide dismutase and cytochrome c oxidase. Reduced eNOS and antioxidant gene expression, impaired endothelial function, and elevated blood pressure in animals fed a soy-deficient diet was reversed after refeeding them an SP diet for 6 months. Our findings suggest that an SP diet increases eNOS and antioxidant gene expression in the vasculature and other tissues, resulting in reduced oxidative stress and increased NO bioavailability. The improvement in endothelial function, increased gene expression, and reduced blood pressure by soy isoflavones have implications for alternative therapy for postmenopausal women and patients at risk of coronary heart disease.

Modulation of PGF2alpha- and hypoxia-induced contraction of rat intrapulmonary artery by p38 MAPK inhibition: a nitric oxide-dependent mechanism

The mechanisms through which p38 mitogen-activated protein kinase (p38 MAPK) is involved in smooth muscle contraction remain largely unresolved. We examined the role of p38 MAPK in prostaglandin F(2alpha) (PGF(2alpha))-induced vasoconstriction and in hypoxic pulmonary vasoconstriction (HPV) of rat small intrapulmonary arteries (IPA). The p38 MAPK inhibitors SB-203580 and SB-202190 strongly inhibited PGF(2alpha)-induced vasoconstriction, with IC(50)s of 1.6 and 1.2 microM, whereas the inactive analog SB-202474 was approximately 30-fold less potent. Both transient and sustained phases of HPV were suppressed by SB-203580, but not by SB-202474 (both 2 microM). Western blot analysis revealed that PGF(2alpha) (20 microM) increased phosphorylation of p38 MAPK and of heat shock protein 27 (HSP27), and this was abolished by SB-203580 but not by SB-202474 (both 2 microM). Endothelial denudation or blockade of endothelial nitric oxide (NO) synthase with N(omega)-nitro-L-arginine methyl ester (L-NAME) significantly suppressed the relaxation of PGF(2alpha)-constricted IPA by SB-203580, but not by SB-202474. Similarly, the inhibition of HPV by SB-203580 was prevented by prior treatment with L-NAME. SB-203580 (2 microM), but not SB-202474, enhanced relaxation-induced by the NO donor S-nitroso-N-acetylpenicillamine (SNAP) in endothelium-denuded IPA constricted with PGF(2alpha). In alpha-toxin-permeabilized IPA, SB-203580-induced relaxation occurred in the presence but not the absence of the NO donor sodium nitroprusside (SNP); SB-202474 was without effect even in the presence of SNP. In intact IPA, neither PGF(2alpha)- nor SNAP-mediated changes in cytosolic free Ca(2+) were affected by SB-203580. We conclude that p38 MAPK contributes to PGF(2alpha)- and hypoxia-induced constriction of rat IPA primarily by antagonizing the underlying Ca(2+)-desensitizing actions of NO.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

Euhydric hypercapnia increases vasoreactivity of rat pulmonary arteries via HCO3- transport and depolarisation

OBJECTIVE

To examine whether altered PCO2 or HCO3- at normal pH potentiate agonist-induced vasoconstriction of small pulmonary arteries, and if so to determine the mechanism.

METHODS

Small intrapulmonary arteries (IPA) from rats were mounted on a myograph and PGF2alpha (3 microM)-induced tension recorded before and 40 min after replacing normal bath solution (5% CO2, 24 mM [HCO3-], pH 7.4) with one containing either normal [HCO3-] (24 mM) gassed with 10% CO2 (pH 7.12; hypercapnic acidosis) or high [HCO3-] (48 mM) gassed with 10% CO2 (pH 7.4; euhydric hypercapnia).

RESULTS

Hypercapnic acidosis had no significant effect on the response of IPA to PGF2alpha. Euhydric hypercapnia however caused a substantial approximately 5.5-fold potentiation of the response (n=17, p<0.001) in the majority of preparations, whilst 20% of IPA (11 of 58) developed a slow spontaneous vasoconstriction after approximately 20 min. No equivalent responses to euhydric hypercapnia were observed in either mesenteric or renal arteries. Both the potentiation of PGF2alpha-induced vasoconstriction and the spontaneous vasoconstriction in IPA were inhibited by the L-type channel blocker diltiazem (10 microM). The potentiation was also suppressed by DIDS, an inhibitor of anion transporters, removal of extracellular Na+, and anthracene-9-carboxylic acid (A9C; 200 microM), reported to inhibit Ca2+-activated Cl- channels. Inhibition of nitric oxide synthase with L-NAME (100 microM) did not prevent potentiation. Depolarisation with 20 mM [K+] mimicked the effect of euhydric hypercapnia in that it also potentiated the response to PGF(2alpha) (>sixfold, n=6).

CONCLUSIONS

Euhydric hypercapnia increases vasoreactivity of IPA, but not mesenteric or renal arteries, via a mechanism involving Na+-dependent HCO3- transport, activation of Ca2+-dependent Cl- channels, and subsequent depolarisation. These results may have consequences for patients with CO2-retaining chronic respiratory disease where plasma [HCO3-] is raised following renal compensation, and could explain the increased propensity to pulmonary hypertension and increased mortality in such patients.

Modulation of potassium current characteristics in human myometrial smooth muscle by 17beta-estradiol and progesterone

The K(+) channel currents are important modulators of smooth muscle membrane potential and excitability. We assessed whether voltage-gated K(+) currents from human myometrium are regulated by placental steroid hormones during pregnancy and labor. Pregnant human myometrial cells were isolated from samples obtained at cesarean section. Primary cultured cells were treated with 100 nM 17beta-estradiol, 1 microM progesterone, or both hormones in combination for 24 h. Acute effects of the two hormones were also determined. The K(+) currents were recorded using the standard whole-cell, patch-clamp technique. Primary cultures possessed both delayed rectifier (I(KV)) and A-like (I(KA)) voltage-gated K(+) currents. The 24-h 17beta-estradiol treatment caused a hyperpolarizing shift in the steady-state inactivation of both I(KV) and I(KA). Progesterone treatment also shifted the inactivation of I(KA) and increased I(KV) amplitude by 60%-110%. Conversely, the combined treatment had no effect on these currents. Neither 17beta-estradiol (0.1-1 microM) nor progesterone (1-5 microM) had any effect on the K(+) current when applied acutely. These results show that 17beta-estradiol should inhibit myometrial K(+) channel activity, whereas progesterone is likely to have the opposite effect. These results are consistent with the respective procontractile and proquiescence roles for 17beta-estradiol and progesterone in human uterus during pregnancy.

Mechanism of effect of extracellular pH on L-type Ca(2+) channel currents in human mesenteric arterial cells

Extracellular pH (pH(o)) influences vasoconstriction partly by modulating Ca(2+) influx through voltage-gated Ca(2+) channels in the vasculature. The mechanism of this effect of pH(o) is, however, controversial. Using the whole cell voltage-clamp technique, we examined the influence of pH(o) on L-type Ca(2+) channel currents in isolated human mesenteric arterial myocytes. Acidification to pH 6.2 and alkalinization to 8.2 from 7.2 decreased by approximately 50% and increased by 25-30%, respectively, the peak amplitude of Ca(2+) and Ba(2+) currents (1.5 and 10 mM), with an apparent pK(a) of 6.8. Activation and inactivation of Ca(2+) and Ba(2+) currents were shifted toward positive membrane voltages during acidification and in the opposite direction during alkalinization. The relationship between the current amplitude and shifts in the gating parameters in solutions of different pH(o) conformed closely to that predicted by the Gouy-Chapman model, in which the divalent cation concentration at the outer surface of the membrane varies with the extent to which protons neutralize the membrane surface potential.

Voltage-gated K+ currents in freshly isolated myocytes of the pregnant human myometrium

1. Voltage-gated K+ currents in human myometrium are not well characterized, and were therefore investigated, using the whole-cell patch clamp technique, in freshly isolated myometrial smooth muscle cells from pregnant women at term. 2. Three types of voltage-gated K+ currents were identified. IK1 was a 4-aminopyridine-insensitive current with a negative half-inactivation (V0.5 = -61 to -67 mV) and negative activation characteristics (threshold between -60 and -40 mV) and slow kinetics. IK2 was a 4-aminopyridine-sensitive current (half-maximal block at approximately 1 mM) with relatively positive half-inactivation (V0.5 = -30 mV) and activation characteristics (threshold between -40 and -30 mV) and faster kinetics. IK,A was a 4-aminopyridine-sensitive current with a negative inactivation and very fast inactivation kinetics. 3. Both IK1 and IK2 were sensitive to high concentrations of tetraethylammonium (half-maximal block at approximately 3 mM) and low concentrations of clofilium (half-maximal block by 3-10 microM). 4. IK1 and IK2 were unevenly distributed between myometrial cells, most cells possessing either IK1 (30 cells) or IK2 (24 cells) as the predominant current. 5. The characteristics of these currents suggest a possible function in the control of membrane potentials and smooth muscle quiescence in the pregnant human myometrium.

Differential effects of insulin-sensitizers troglitazone and rosiglitazone on ion currents in rat vascular myocytes

Insulin-sensitizing thiazolidinediones such as troglitazone and pioglitazone have been shown to lower blood pressure in vivo and cause vasorelaxation in vitro. Rosiglitazone (BRL 49653) is a novel thiazolidinedione which has been reported not to cause vasoleraxation. We therefore compared the effects of troglitazone and rosiglitazone on Ca2+ and K+ currents in rat aorta and pulmonary artery smooth muscle cells. Currents were recorded with the conventional whole cell patch clamp technique. Both drugs reduced the voltage-gated (L-type) Ca2+ current in rat aorta cells, with half-maximal current inhibition by troglitazone and rosiglitazone at 2 and 10 microM, respectively. Troglitazone, 2 microM and rosiglitazone, 20 microM caused a similar hyperpolarizing shift of 12 mV in the potential-dependence of Ca2+ current availability. Troglitazone (20 microM) produced a marked block of the tetraethylammonium- and paxilline-sensitive Ca2+ activated K+ current, while rosiglitazone (20 microM and 60 microM) slightly enhanced this current. Rat pulmonary artery smooth muscle cells have a prominent delayed rectifier K+ current. Troglitazone produced a potent block of this current (half-maximal inhibition at <1 microM), while rosiglitazone caused a smaller inhibition at 10 and 60 microM. These results show that troglitazone has relatively potent blocking effects on a wide variety of ion currents in vascular smooth muscle cells. Rosiglitazone exerts less potent, but similar effects on the Ca2+ current and delayed rectifier K+ current, but it enhances the Ca2+ activated K+ current. reserved.

Effect of nimesulide and indomethacin on contractility and the Ca2+ channel current in myometrial smooth muscle from pregnant women

The non-steroidal anti-inflammatory drug (NSAID) indomethacin inhibits both constitutive and inducible forms of cyclo-oxygenase (COX-1 and COX-2, respectively), while nimesulide is a selective COX-2 inhibitor. Uterine COX-2 is upregulated before and during term and pre-term labour, and prostaglandins play a crucial role in parturition. We therefore evaluated the effects of these drugs on myometrial contractility and the voltage-gated Ca2+ channel current in tissue strips and isolated human myometrial smooth muscle cells (HMSMC) from myometrial biopsies taken with informed consent from women undergoing caesarean section at term (not in labour). Nimesulide and indomethacin caused almost complete inhibition of spontaneous myometrial contractions at concentrations of 100 and 300 microM, respectively. The Ca2+ channel current was inhibited in a concentration-dependent manner by both drugs, with a 40% reduction of the current at 100 microM nimesulide and 300 microM indomethacin. Nimesulide also accelerated the decay of the Ca2+ channel current. The inhibition of the Ca2+ channel current by 100 microM nimesulide and 300 microM indomethacin was unaffected by the presence of either PGF2alpha or PGE2 (30 microM), and was of similar magnitude whether 10 mM Ba2+ or 1.5 mM Ca2+ was used as the charge carrier. The concentrations of indomethacin and nimesulide required to suppress spontaneous contractility in human pregnant myometrium were much higher than those necessary to inhibit prostaglandin production. The results suggest that both nimesulide and indomethacin inhibit myometrial contractility via mechanisms independent of cyclo-oxygenase inhibition. Blockade of the Ca2+ current may contribute to this effect.

Effects of the 5-lipoxygenase activating protein inhibitor MK886 on voltage-gated and Ca2+-activated K+ currents in rat arterial myocytes

1. The effects on the voltage-gated (IK) and Ca2+ activated (I(K,Ca)) K+ currents in rat arterial myocytes of the 5-lipoxygenase activating protein (FLAP) inhibitor MK886, and its inactive analogue L583,916 were evaluated. 2. In rat pulmonary arterial myocytes (RPAMs), MK886 caused a concentration-dependent reduction of the IK, with little obvious change in the kinetics of the current. Half maximal current block was observed at 75 nM MK886. 3. MK886 application led to a concentration-dependent increase in the amplitude of the TEA-sensitive I(K,Ca) current and single channel activity in RPAMs in whole cell and inside-out configurations, respectively. The threshold concentration for this effect was approximately 300 nM and a maximal 4-5 fold increase was observed at 10 microM MK886. MK886 also increased I(K,Ca) in rat mesenteric arterial myocytes (RMAMs). 4. L538,916, an analogue of MK886 which does not block FLAP, had no effect on either IK or I(K,Ca) at a concentration of 10 microM. 5. Leukotriene C4 (100 nM) had no effect on either IK or I(K,Ca) in RPAMs. MK886 produced its usual increase in I(K,Ca) and also blocked IK, in the presence of leukotriene C4. Similarly, leukotriene E4 (100 nM) did not alter the amplitude of IK. Also, the nonselective leukotriene receptor antagonist ICI 198,615 (3 microM) did not affect IK in RPAMs, and did not affect the response to MK886. 6. Arachidonic acid (10 microM) enhanced I(K,Ca) in both RPAMs and RMAMs. 7. The results show that MK886 markedly affects both IK and I(K,Ca) in a manner similar to that of arachidonic acid and independent of the endogenous production of leukotrienes. It is therefore possible that MK886, which is thought to compete with arachidonic acid for its binding to FLAP, may similarly occupy arachidonic acid binding sites on these K+ channels, and mimic its effects. Alternatively, MK886 might act via non-selective effects on other arachidonic acid metabolites which could modify K+ channel function.

Association of gestational diabetes with abnormal maternal vascular endothelial function

OBJECTIVE

To evaluate vascular endothelial function in isolated small arteries from women with gestational diabetes.

METHODS

Small subcutaneous arteries (mean luminal diameter approximately 250 microns) were dissected from biopsies obtained at caesarean section in 14 normotensive women with gestational diabetes and in 18 normotensive nondiabetic pregnant women. Vascular function was determined after mounting the arteries on a small vessel myograph.

RESULTS

Pre-constricted arteries from gestational diabetic pregnant women demonstrated poor relaxation to acetylcholine, an endothelium-dependent vasodilator (pEC50, mean [SE], 6.98 [0.10] vs normal pregnant, 7.28 [0.08], P < 0.03; % maximum relaxation, median [range], 88.2 [42.4-99.4] vs normal pregnant 94.2 [71.8-100.0], P < 0.01). In the presence of indomethacin relaxation to acetylcholine was similar in both groups suggesting a deficiency in dilator prostaglandin synthesis in the arteries from the diabetic women. The nitric oxide synthase inhibitor NG-monomethyl-L-arginine further reduced sensitivity of arteries to acetylcholine but to a similar degree in both normal pregnant and gestational diabetic women. Relaxation to sodium nitroprusside, an indicator of sensitivity of the vascular smooth muscle to nitric oxide, was similar in both groups.

CONCLUSIONS

Maternal vascular endothelial dysfunction may contribute to the increased incidence of cardiovascular disorders in women with gestational diabetes.

Bradykinin-mediated relaxation of isolated maternal resistance arteries in normal pregnancy and preeclampsia

OBJECTIVE

The aim of the study was to investigate bradykinin-mediated vasodilator function in small arteries from normotensive pregnant and nonpregnant women and from women with preeclampsia.

STUDY DESIGN

Small subcutaneous arteries (approximately 250 microns luminal diameter) were dissected from biopsy specimens obtained at cesarean section from 24 normotensive pregnant women and 6 women with preeclampsia and during abdominal surgery in 15 nonpregnant women. Vascular function was assessed after arteries were mounted on a small vessel myograph.

RESULTS

Preconstricted arteries from normotensive pregnant women demonstrated enhanced relaxation to bradykinin compared with those from nonpregnant women (p < 0.05), whereas arteries from women with preeclampsia showed blunted responses compared with those from normotensive pregnant women (P < 0.01). Relaxation in all groups was attenuated in the presence of the nitric oxide synthase inhibitor N omega-nitro-L-arginine so that it became similar in the three groups. Indomethacin had a small but significant inhibitory effect on bradykinin-induced relaxation, but this component of relaxation was no different among groups. Sensitivity of arteries to norepinephrine and sodium nitroprusside showed no significant differences in the three groups of women.

CONCLUSION

This study provides evidence for an increase in bradykinin-mediated nitric oxide synthesis from the vascular endothelium of small arteries from the peripheral circulation of normotensive pregnant women and a relative reduction in women with preeclampsia. In turn, these changes may contribute to vasodilation in normal pregnancy and elevation of the blood pressure in preeclampsia.

Myogenic and flow-mediated responses in isolated mesenteric small arteries from pregnant and nonpregnant rats

OBJECTIVES

Responses to pressure, agonist-induced constriction, endothelium-dependent vasodilators, and shear stress were investigated in resistance-sized mesenteric arteries in vitro from late-pregnant and nonpregnant rats.

STUDY DESIGN

Myogenic tone was determined in arteries mounted on a pressure myograph by evaluating the response to incremental increases in luminal pressure in resting arteries and arteries preconstricted with norepinephrine (10(-6) mol/L). Flow-mediated dilation was also investigated in the presence and absence of a nitric oxide synthase inhibitor, L-N(omega)-nitro-L-arginine methyl ester. Constrictor responses to norepinephrine (10(-9) to 10(-5) mol/L), were examined with a small vessel myograph. Responses of preconstricted arteries to acetylcholine (10(-9) to 10(-5) mol/L), bradykinin (10(-9) to 10(-5) mol/L), and sodium nitroprusside (10(-9) to 10(-5) mol/L) were also assessed.

RESULTS

Myogenic tone was only demonstrable in response to increasing pressure when arteries were preconstricted with norepinephrine (10(-6) mol/L) and was similar in arteries from both pregnant and nonpregnant rats. Flow-mediated dilation was greater in pregnant rats and was reduced by L-N(omega)-nitro-L-arginine methyl ester. Arteries from the pregnant rats demonstrated a reduced constrictor response to norepinephrine. Responses to acetylcholine were similar in both groups, but arteries from the pregnant rats showed enhanced relaxation to bradykinin.

CONCLUSIONS

The data substantiate previous studies indicating reduced constrictor responses in pregnancy but provide no evidence to suggest that blunted myogenic responses contribute to reduced vascular resistance in pregnancy. The results indicate that flow-mediated nitric oxide release may contribute to vasodilation in pregnant rats. Different responses to two endothelium-dependent vasodilators suggest that specific alterations in signal transduction pathways may influence nitric oxide synthesis in pregnancy.

Regional changes in angiotensin II receptor density after experimental myocardial infarction

The plasma and cardiac renin-angiotensin systems may be activated after myocardial infarction. The myocardium may therefore be exposed to increased concentrations of angiotension II, which may contribute to myocardial injury. The purpose of this study was to identify the potential sites of action of angiotensin II in the infarcted heart. Myocardial infarction was induced in rats by left coronary artery ligation, and the hearts were removed for study after 18 h, 7 days, or 8 months. The regional ventricular angiotensin II receptor density was assessed by [125I](Sar1,Ile8)angiotensin II binding and quantitative autoradiography. The [125I](Sar1,Ile8)angiotensin II binding was unchanged at 18 h, but was increased at 7 days in the infarcted region of the left ventricle (73.2 +/- 3.2 amol/mm2, mean +/- S.E.M.) compared with the non-infarcted region (1.6 +/- 0.2 amol/mm2, P < 0.0001) and with the left ventricular myocardium of sham-operated control animals (1.3 +/- 0.1 amol/mm2, P < 0.0001). The increased [125I](Sar1,Ile8)angiotensin II binding density was still present, but diminished, at 8 months after coronary ligation (49.0 +/- 5.7 amol/mm2, P < 0.0001 v control, P = 0.0058 v 7-day infarcts). The increased binding of [125I](Sar1,Ile8)angiotensin II was antagonised by losartan, an AT1 receptor antagonist, but not by an AT2 receptor antagonist. Microautoradiography of [125I](Sar1,Ile8) angiotensin II, and assessment of collagen deposition using picrosirius staining and immunostaining demonstrated that the regional increase in AT1 receptor density in the infarcted region of myocardium was associated with fibroblast infiltration and collagen deposition. The infarct scar and the cardiac fibroblasts within it express high levels of angiotension II receptors and therefore represent potential targets for the actions of angiotensin II after myocardial infarction.

Evidence for ETA and ETB receptors in rat skin and an investigation of their function in the cutaneous microvasculature

1. The relative contribution of ETA and ETB receptors in the response of rat skin to endothelins was investigated by use of the selective ETB agonist IRL-1620 and the selective ETA antagonist BQ-123. 2. Binding data suggest the presence of ETA and ETB receptors as preincubation with [Ala3,11,18Nle7]-endothelin-1 reduced ET-1 binding by approximately 40%. 3. Intradermal injection of endothelin-1 (ET-1, 1-10 pmol/site) and ET-3 (3-100 pmol/site) induced a dose-dependent decrease in local blood flow assessed by 133Xe clearance at test sites in rat skin. 4. The endothelin analogue [Ala3,11,18Nle7]-ET-1 (30-1000 pmol/site) induced significant vasoconstriction (P < 0.05) at the highest doses used and the selective ETB receptor agonist, IRL-1620 [Suc[Glu9,Ala11,15] endothelin (8-21)], (0.01-100 pmol/site) acted in a potent manner to induce a significant (P < 0.01) dose-dependent decrease in 133Xe clearance. 5. Co-injection with the selective ETA receptor antagonist, BQ-123 (1 nmol/site), completely abolished the vasoconstriction to ET-1 and partially to ET-3, but had no effect on IRL-1620-induced vasoconstriction. In addition, IRL-1620 responses were not altered at sites treated with submaximal doses of a nitric oxide synthase inhibitor or a prostaglandin synthase inhibitor. 6. ET-1 and IRL-1620 (100 fmol-1 pmol/site) did not induce oedema formation as measured by [125I]-albumin accumulation in the presence or absence of the vasodilator, calcitonin gene-related peptide (CGRP). ET-1 (1-3 pmol/site) inhibited substance P-induced oedema formation and this effect,suggested to be secondary to a vasoconstrictor effect, was significantly reversed by BQ-123 (1 nmol/site).7. The findings in this study indicate that there are ETA and ETB receptors in rat skin and agents which activate either receptor act to mediate a decrease in cutaneous blood flow, but have no effect on increased microvascular permeability.

Angiotensin II (AT1) vascular binding sites in human placentae from normal-term, preeclamptic and growth retarded pregnancies

Angiotensin II (ANG II) is a potent vasoconstrictor in isolated human placental cotyledons and may contribute to the regulation of fetoplacental perfusion. We have used quantitative in vitro receptor autoradiography to examine antagonist ((Sar1,Ile8)-[125I]ANG II) and agonist ligand ([125I]ANG II) binding sites in normal-term, preeclamptic and fetal (intrauterine) growth retarded pregnancies. A similar distribution of binding sites was demonstrated using both ligands, localized to blood vessels in placental villi. Binding density was inversely related to vessel size, being significantly greater on microvessels in distal regions of the villous tree than on proximal vessels in main stem villi. Binding sites exhibited the characteristics of the AT1 class of ANG II receptor, ligand binding being sensitive to dithiothreitol, completely inhibited by nonpeptide AT1 antagonists (Losartan, EXP3174 and SKF108566) and not inhibited by the AT2 antagonist (PD123319). Guanine nucleotides also inhibited [125I]ANG II binding and abolished the high affinity component of agonist inhibition of (Ser1,Ile8)-[125I]ANG II binding, indicating G protein coupling. The capacity and affinity of the binding sites were significantly lower in placentae from pregnancies complicated by preeclampsia and intrauterine growth retardation compared to that in normal-term controls. These differences were apparently not due to prior receptor occupancy by endogenous ligand, but may reflect activation of the placental renin-angiotensin system and receptor down-regulation. Locally generated ANG II, acting via AT1 receptors, may contribute to the regulation of fetoplacental blood flow and influence placental perfusion in preeclamptic and growth retarded pregnancies.

AT1 receptor characteristics of angiotensin analogue binding in human synovium

1. Angiotensin II (AII) reduces blood flow, modulates vascular remodelling and is a growth factor. Human inflammatory arthritides are characterized by synovial hypoperfusion, hypoxia and proliferation. We aimed to localize and characterize receptors for AII in human synovium. 2. We used quantitative in vitro receptor autoradiography with [125I]-(Sar1, Ile8)AII and [125I]-AII on human synovium from patients with chondromalacia patellae, osteoarthritis and rheumatoid arthritis. 3. [125I]-(Sar1, Ile8)AII and [125I]-AII bound to similar sites on synovial blood vessels, lining cells and stroma. Binding to microvessels (< 100 microns diameter) was more dense than to arteriolar media, and vascular binding was more dense than that to lining cells and stroma. 4. Microvessels and arterioles which displayed angiotensin converting enzyme-like immunoreactivity also displayed specific binding of [125I]-(Sar1, Ile8)AII. 5. Specific binding of [125I]-(Sar1, Ile8)AII to each structure was completely inhibited by 10 microM dithiothreitol and was inhibited by unlabelled ligands with the rank order of potency (Sar1, Ile8)AII > AII > losartan = SKF108566 > PD123319 indicating an AT1 subclass of angiotensin receptor. 6. GTP gamma S (1 microM) abolished specific binding of [125I]-AII and abolished the high affinity component of the binding inhibition curve for AII against [125I]-(Sar1, Ile8)AII, indicating G protein coupling. 7. The distribution of [125I]-(Sar1, Ile8)AII binding sites was similar in all disease groups and no significant differences in binding densities, affinities or specificities were observed between disease groups. 8. Locally generated AII may act on synovial AT1 receptors to modulate synovial perfusion and growth. Specific AT1 receptor antagonists should help elucidate the role of angiotensins in human arthritis.

Characterization of endothelin-binding sites in human skin and their regulation in primary Raynaud's phenomenon and systemic sclerosis

Endothelin (ET), which mediates vasoconstrictor and vasodilator activities via multiple receptor subtypes, has been implicated in the control of blood flow and vascular tone in human skin, and possibly in the abnormal vasoconstrictor response in primary Raynaud's phenomenon and systemic sclerosis. Using in vitro autoradiography we have examined the endothelin-binding characteristics and receptor subtypes of human skin, and sought to provide evidence for endothelin receptor regulation in skin from patients with primary or secondary Raynaud's phenomenon. Specific 125I-ET-1 and 125I-ET-3 binding sites were localized to microvessels of the sub-epidermal plexus and dermal papillae, larger blood vessels, sweat glands, epidermis, and hair follicles. Both ETA and ETB receptors were demonstrated in microvessels and other structures. ET receptor heterogeneity in skin vasculature suggests a role for ET as an autocrine/paracrine regulator of vasoconstrictor and vasodilator pathways in human skin. The presence of binding sites in epidermis and hair follicles suggests a possible mitogenic function for endothelin in human skin. Endothelin-binding density was significantly higher (p < 0.05) in microvessels of skin from patients with systemic sclerosis but not significantly different in Raynaud's phenomenon patients, compared to controls. Lack of down regulation of ET receptors in Raynaud's phenomenon and systemic sclerosis may contribute to the pathogenesis of vasospasm in these diseases.

Regional distribution and regulation of [125I]calcitonin gene-related peptide binding sites in coronary arteries

Quantitative in vitro autoradiographic techniques were used to localize and characterize 125I-labelled human calcitonin gene-related peptide ([125I]hCGRP) binding sites in sections of bovine left anterior descending coronary artery (LAD). Specific high affinity (Kd 0.4 nM) [125I]hCGRP binding sites were localized to the media of both epicardial and myocardial coronary arteries. Binding site density was greater in distal epicardial and myocardial arteries than in proximal epicardial regions of the LAD. Binding sites exhibited a significantly higher affinity for alpha-hCGRP (Ki 1.1 nM) than for hCGRP-(8-37) (Ki 7.0 nM) and [Cys(ACM)2,7]hCGRP (Ki 27.4 nM). Guanosine-5'-O-(3-thiotriphosphate) inhibited [125I]hCGRP binding in a concentration-dependent manner. Extrinsic denervation of the bovine heart resulted in a depletion of CGRP-like immunoreactive perivascular nerve fibres and an increase in the density of coronary artery [125I]hCGRP binding sites (P = 0.0092). The regional distribution of binding sites in human coronary arteries differed from that observed in bovine and porcine vessels. It is concluded that selective, G protein-coupled, CGRP receptors are present in the media of bovine coronary arteries; there are both regional and species differences in the distribution of CGRP binding sites in coronary arteries and endogenous CGRP may exert a tonic influence on coronary vasomotor tone.

Autoradiographic localization and analysis of endothelin-1 binding sites in human synovial tissue

OBJECTIVE

To determine the localization of endothelin binding sites and immunoreactivity in human synovial tissues.

METHODS

Quantitative in vitro autoradiographic and immunohistochemical techniques were used to localize and characterize 125I-labeled endothelin-1 (125I-ET-1) binding sites and endothelin-like immunoreactivity in sections of rheumatoid, osteoarthritic, and normal synovium.

RESULTS

Specific 125I-ET-1-binding sites, characteristic of the ETA receptor, were localized to the media of synovial blood vessels in all 3 groups. No difference was found in vascular binding site density in rheumatoid and osteoarthritic synovium. Endothelin-like immunoreactivity was localized to endothelial cells in blood vessels displaying 125I-ET-1 binding sites.

CONCLUSION

We conclude that endothelin may act locally, modulating synovial perfusion and exacerbating hypoxia in chronic arthritis.