Coronary artery hypoxic vasorelaxation is augmented by perivascular adipose tissue through a mechanism involving hydrogen sulphide and cystathionine-ß-synthase.

AIM: Hypoxia causes vasodilatation of coronary arteries which protects the heart from ischaemic damage through mechanisms including the generation of hydrogen sulphide (H2 S), but the influence of the perivascular adipose tissue (PVAT) and myocardium is incompletely understood. This study aimed to determine whether PVAT and the myocardium modulate the coronary artery hypoxic response and whether this involves hydrogen sulphide. METHODS: Porcine left circumflex coronary arteries were prepared as cleaned segments and with PVAT intact, myocardium intact or both PVAT and myocardium intact, and contractility investigated using isometric tension recording. Immunoblotting was used to measure levels of H2 S-synthesizing enzymes: cystathionine-ß-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulphurtransferase (MPST). RESULTS: All three H2 S-synthesizing enzymes were detected in the artery and myocardium, but only CBS and MPST were detected in PVAT. Hypoxia elicited a biphasic response in cleaned artery segments consisting of transient contraction followed by prolonged relaxation. In arteries with PVAT intact, hypoxic contraction was attenuated and relaxation augmented. In arteries with myocardium intact, hypoxic contraction was attenuated, but relaxation was unaffected. In replacement experiments, replacement of dissected PVAT and myocardium attenuated artery contraction and augmented relaxation to hypoxia, mimicking the effect of in situ PVAT and indicating involvement of a diffusible factor(s). In arteries with intact PVAT, augmentation of hypoxic relaxation was reversed by amino-oxyacetate (CBS inhibitor), but not DL-propargylglycine (CSE inhibitor) or aspartate (inhibits MPST pathway). CONCLUSION: PVAT augments hypoxic relaxation of coronary arteries through a mechanism involving H2 S and CBS, pointing to an important role in regulation of coronary blood flow during hypoxia.

A critical role for cystathionine-ß-synthase in hydrogen sulfide-mediated hypoxic relaxation of the coronary artery.

Hypoxia-induced coronary artery vasodilatation protects the heart by increasing blood flow under ischemic conditions, however its mechanism is not fully elucidated. Hydrogen sulfide (H2S) is reported to be an oxygen sensor/transducer in the vasculature. The present study aimed to identify and characterise the role of H2S in the hypoxic response of the coronary artery, and to define the H2S synthetic enzymes involved. Immunoblotting and immunohistochemistry showed expression of all three H2S-producing enzymes, cystathionine-ß-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (MPST), in porcine coronary artery. Artery segments were mounted for isometric tension recording; hypoxia caused a transient endothelium-dependent contraction followed by prolonged endothelium-independent relaxation. The CBS inhibitor amino-oxyacetate (AOAA) reduced both phases of the hypoxic response. The CSE inhibitor dl-propargylglycine (PPG) and aspartate (limits MPST) had no effect alone, but when applied together with AOAA the hypoxic relaxation response was further reduced. Exogenous H2S (Na2S and NaHS) produced concentration-dependent contraction followed by prolonged relaxation. Responses to both hypoxia and exogenous H2S were dependent on the endothelium, NO, cGMP, K+ channels and Cl-/HCO3- exchange. H2S production in coronary arteries was blocked by CBS inhibition (AOAA), but not by CSE inhibition (PPG). These data show that H2S is an endogenous mediator of the hypoxic response in coronary arteries. Of the three H2S-producing enzymes, CBS, expressed in the vascular smooth muscle, appears to be the most important for H2S generated during hypoxic relaxation of the coronary artery. A contribution from other H2S-producing enzymes only becomes apparent when CBS activity is inhibited.

BJP is linking its articles to the IUPHAR/BPS Guide to PHARMACOLOGY.

LINKED EDITORIALS: This Editorial is part of a series. To view the other Editorials in this series, visit: http://onlinelibrary.wiley.com/doi/10.1111/bph.12956/abstract; http://onlinelibrary.wiley.com/doi/10.1111/bph.12954/abstract; http://onlinelibrary.wiley.com/doi/10.1111/bph.12955/abstract and http://onlinelibrary.wiley.com/doi/10.1111/bph.12856/abstract. VIDEO: To view the video on the IUPHAR/BPS Guide to PHARMACOLOGY, visit: https://www.youtube.com/watch?v=Qhy3q33VtRI.

Evaluation of three-dimensional root surface changes and resorption following rapid maxillary expansion: a cone beam computed tomography investigation.

OBJECTIVES: To evaluate root surface changes and resorption following toothborne rapid maxillary expansion (RME) using cone beam computed tomography (CBCT). SETTING AND SAMPLE POPULATION: The Department of Orthodontics at The University of Texas Health Science Center. Twenty-four consecutively treated patients (mean age: 12.8 years) requiring maxillary expansion. MATERIAL AND METHODS: An observational cohort included 48 CBCT images collected prior to (T1) and 4.8 months after (T2) RME from the study sample. Maxillary (study group) and mandibular (control group) first molars (n=48) and first premolars (n=48) were segmented and digitally registered using a 'best-fit' algorithm. Linear surface and volumetric changes between the study and control groups were compared using independent sample t-tests. Additionally, individual root length measurements were compared between the T1 and T2 images in each group using paired t-tests. RESULTS: All study teeth had significant changes for the evaluation of maximum linear surface area and volumetric changes as compared to control teeth (p<0.05). On average, premolars and molars in the study group experienced a root shortening of 0.36-0.52 mm (p<0.05). Color-coded diagrams demonstrated thinning and resorption occurring primarily at the apex and buccal aspects of the roots. Severity of these changes was individual-specific, as root resorption patterns were non-uniform. CONCLUSION: Significant volume loss, linear surface area changes, and thinning/shortening of maxillary first molar and premolar roots were common findings with the use of toothborne RME therapy.

Effects of pro-inflammatory cytokines on cannabinoid CB1 and CB2 receptors in immune cells.

AIMS: To investigate the regulation of cannabinoid receptors CB1 and CB2 on immune cells by pro-inflammatory cytokines and its potential relevance to the inflammatory neurological disease, multiple sclerosis (MS). CB1 and CB2 signalling may be anti-inflammatory and neuroprotective in neuroinflammatory diseases. Cannabinoids can suppress inflammatory cytokines but the effects of these cytokines on CB1 and CB2 expression and function are unknown. METHODS: Immune cells from peripheral blood were obtained from healthy volunteers and patients with MS. Expression of CB1 and CB2 mRNA in whole blood cells, peripheral blood mononuclear cells (PBMC) and T cells was determined by quantitative real-time polymerase chain reaction (qRT-PCR). Expression of CB1 and CB2 protein was determined by flow cytometry. CB1 and CB2 signalling in PBMC was determined by Western blotting for Erk1/2. RESULTS: Pro-inflammatory cytokines IL-1ß, IL-6 and TNF-α (the latter likely NF-κB dependently) can upregulate CB1 and CB2 on human whole blood and peripheral blood mononuclear cells (PBMC). We also demonstrate upregulation of CB1 and CB2 and increased IL-1ß, IL-6 and TNF-α mRNA in blood of patients with MS compared with controls. CONCLUSION: The levels of CB1 and CB2 can be upregulated by inflammatory cytokines, which can explain their increase in inflammatory conditions including MS.

Effects of NAD at purine receptors in isolated blood vessels.

Nicotinamide adenine dinucleotide (NAD) belongs to the family of naturally occurring adenine dinucleotides, best known for their various intracellular roles. However, there is evidence that they can also be released from cells to act as novel extracellular signalling molecules. Relatively little is known about the extracellular actions of NAD, especially in the cardiovascular system. The present study investigated the actions of NAD in the rat thoracic aorta, porcine coronary artery and porcine mesenteric arteries, mounted in organ baths for isometric tension recording. In the rat thoracic aorta and porcine coronary artery, NAD caused endothelium-independent concentration-dependent vasorelaxations which were unaffected by palmitoylCoA, a P2Y1 receptor antagonist, but which were blocked by CGS15943, a non-selective adenosine receptor antagonist. In the porcine coronary artery, NAD-evoked relaxations were abolished by SCH58261, a selective A2A receptor antagonist. In the rat thoracic aorta, NAD-evoked relaxations were attenuated by A2A receptor antagonism with SCH58261 but were unaffected by an A2B receptor antagonist, MRS1754. In contrast, in the porcine mesenteric artery, NAD-evoked endothelium-independent contractions, which were unaffected by a P2 receptor antagonist, suramin, or by NF449, a P2X1 receptor antagonist, but were attenuated following P2X receptor desensitisation with αß-meATP. In conclusion, the present results show that NAD can alter vascular tone through actions at purine receptors in three different arteries from two species; its molecular targets differ according to the type of blood vessel.

A role for the sodium pump in H2O2-induced vasorelaxation in porcine isolated coronary arteries.

Hydrogen peroxide (H2O2) has been proposed to act as a factor for endothelium-derived hyperpolarization (EDH) and EDH may act as a 'back up' system to compensate the loss of the NO pathway. Here, the mechanism of action of H2O2 in porcine isolated coronary arteries (PCAs) was investigated. Distal PCAs were mounted in a wire myograph and pre-contracted with U46619 (1nM-50µM), a thromboxane A2-mimetic or KCl (60mM). Concentration-response curves to H2O2(1µM-1mM), bradykinin (0.01nM-1µM), sodium nitroprusside (SNP) (10nM-10µM), verapamil (1nM-10µM), KCl (0-20mM) or Ca(2+)-reintroduction (1µM-10mM) were constructed in the presence of various inhibitors. Activity of the Na(+)/K(+)-pump was measured through rubidium-uptake using atomic absorption spectrophotometry. H2O2 caused concentration-dependent vasorelaxations with a maximum relaxation (Rmax) of 100±16% (mean±SEM), pEC50=4.18±0.20 (n=4) which were significantly inhibited by PEG-catalase at 0.1-1.0mM H2O2 (P<0.05). 10mM TEA significantly inhibited the relaxation up to 100µM H2O2 (P<0.05). 60mM K(+) and 500nM ouabain significantly inhibited H2O2-induced vasorelaxation producing a relaxation of 40.8±8.5% (n=5) and 47.5±8.6% (n=6) respectively at 1mM H2O2 (P<0.0001). H2O2-induced vasorelaxation was unaffected by the removal of endothelium, inhibition of NO, cyclo-oxygenase, gap junctions, SKCa, IKCa, BKCa Kir, KV, KATP or cGMP. 100µM H2O2 had no effects on the KCl-induced vasorelaxation or Ca(2+)-reintroduction contraction. 1mM H2O2 inhibited both KCl-induced vasorelaxation and rubidium-uptake consistent with inhibition of the Na(+)/K(+)-pump activity. We have shown that the vascular actions of H2O2 are sensitive to ouabain and high concentrations of H2O2 are able to modulate the Na(+)/K(+)-pump. This may contribute towards its vascular actions.

Distinct mechanisms of relaxation to bioactive components from chamomile species in porcine isolated blood vessels.

German chamomile (Matricaria recutita L.), a widely-used herbal medicine, has been reported to have a wide range of biological effects, including smooth muscle relaxation. The aim of this study was to compare the effects of representative compounds from chamomile (apigenin, luteolin, (-)-α-bisabolol, farnesene, umbelliferone; 3-30 µM) on vascular tone using porcine coronary and splenic arteries mounted for isometric tension recording in isolated tissue baths and precontracted with the thromboxane-mimetic U46619. Apigenin, luteolin, and (-)-α-bisabolol produced slow, concentration-dependent relaxations in both the coronary and splenic arteries that were not blocked by inhibition of nitric oxide synthase or potassium channels. Removal of extracellular calcium inhibited the relaxations to all three compounds, and these compounds also inhibited calcium re-addition-evoked contractions, indicating that the relaxation response may be mediated through inhibition of calcium influx. Apigenin and luteolin, but not (-)-α-bisabolol, enhanced the relaxation to the nitric oxide donor sodium nitroprusside, indicating that apigenin and luteolin may act to regulate cyclic GMP levels. Umbelliferone produced a rapid, transient relaxation in the splenic artery, but not the coronary artery, that was inhibited by L-NAME and removal of the endothelium, suggesting an influence on nitric oxide production. Farnesene, at concentrations up to 30 µM, was without effect in either blood vessel. In conclusion, hydroxylated compounds (apigenin, luteolin and (-)-α-bisabolol) found in chamomile all caused a slow relaxation of isolated blood vessels through an effect on calcium influx. Umbelliferone, on the other hand, produced a rapid, transient relaxation dependent upon release of nitric oxide from the endothelium.

Hydrogen sulphide-induced relaxation of porcine peripheral bronchioles.

BACKGROUND AND PURPOSE: Hydrogen sulphide (H2S) is an endogenous gasotransmitter. Although it has been shown to elicit responses in vascular and other smooth muscle preparations, a role for endogenously produced H2S in mediating airway tone has yet to be demonstrated. Therefore, the aim of this study was to determine whether H2S is produced within the airways and to determine the functional effect on airway tone. EXPERIMENTAL APPROACH: Small peripheral airways (<5 mm in diameter) from porcine lungs were set up in isolated tissue baths, pre-contracted with the muscarinic agonist carbachol, and then exposed to either the H2S donor sodium hydrosulphide (NaHS), or the precursor L-cysteine. H2S production from L-cysteine or 3-mercaptopyruvate in tissue homogenates was measured by the methylene blue assay. Expression of the H2S-synthesizing enzymes cystathionine ß-synthase (CBS), cystathionine γ lyase (CSE) and 3-mercaptopyruvate sulphurtransferase (3-MST) were measured by Western blotting. KEY RESULTS: NaHS caused a large relaxation of the airways, which was inhibited partially by pre-contraction with KCl or exposure to tetraethylammonium, but not glibenclamide, paxilline or 4-aminopyridine. L-cysteine also caused a relaxation of the airways which was inhibited by the CBS inhibitor aminooxyacetic acid. Tissue homogenates from airways exposed to L-cysteine or 3-mercaptopyruvate in vitro showed a significant production of H2S. Western blotting demonstrated immunoreactivity to CBS, CSE and 3-MST enzymes in the airways. CONCLUSIONS AND IMPLICATIONS: These data demonstrate that H2S can be produced endogenously within porcine airways causing relaxation. The mechanism of relaxation depends, in part, on K(+) channel activity.

Antagonism of P2Y1-induced vasorelaxation by acyl CoA: a critical role for palmitate and 3'-phosphate.

BACKGROUND AND PURPOSE: Acyl derivatives of CoA have been shown to act as antagonists at human platelet and recombinant P2Y1 receptors, but little is known about their effects in the cardiovascular system. This study evaluated the effect of these endogenous nucleotide derivatives at P2Y1 receptors natively expressed in rat and porcine blood vessels. EXPERIMENTAL APPROACH: Isometric tension recordings were used to evaluate the effects of CoA, acetyl CoA, palmitoyl CoA (PaCoA) and 3'-dephospho-palmitoyl-CoA on concentration relaxation-response curves to ADP and uridine triphosphate (UTP). A FlexStation monitored ADP- and UTP-evoked calcium responses in HEK293 cells. KEY RESULTS: Acetyl CoA and PaCoA, but not CoA, inhibited endothelium-dependent relaxations to ADP with apparent selectivity for P2Y1 receptors (over P2Y(2/4) receptors) in rat thoracic aorta; PaCoA was more potent than acetyl CoA (331-fold vs. fivefold shift of ADP response curve evoked by 10 µM PaCoA and acetyl CoA, respectively); the apparent pA2 value for PaCoA was 6.44. 3'-dephospho-palmitoyl-CoA (10 µM) was significantly less potent than PaCoA (20-fold shift). In porcine mesenteric arteries, PaCoA and the P2Y1 receptor antagonist MRS2500 blocked ADP-mediated endothelium-dependent relaxations; in contrast, they were ineffective against ADP-mediated endothelium-independent relaxation in porcine coronary arteries (which does not involve P2Y1 receptors). Calcium responses evoked by ADP activation of endogenous P2Y1 receptors in HEK293 cells were inhibited in the presence of PaCoA, which failed to alter responses to UTP (acting at endogenous P2Y(2/4) receptors). CONCLUSIONS AND IMPLICATIONS: Acyl derivatives of CoA can act as endogenous selective antagonists of P2Y1 receptors in blood vessels, and this inhibitory effect critically depends on the palmitate and 3'-ribose phosphate substituents on CoA.

Spinal administration of the monoacylglycerol lipase inhibitor JZL184 produces robust inhibitory effects on nociceptive processing and the development of central sensitization in the rat.

BACKGROUND AND PURPOSE: The cannabinoid receptor-mediated analgesic effects of 2-arachidonoylglycerol (2-AG) are limited by monoacylglycerol lipase (MAGL). 4-nitrophenyl 4-[bis (1,3-benzodioxol-5-yl) (hydroxy) methyl] piperidine-1-carboxylate (JZL184) is a potent inhibitor of MAGL in the mouse, though potency is reportedly reduced in the rat. Here we have assessed the effects of spinal inhibition of MAGL with JZL184 on nociceptive processing in rats. EXPERIMENTAL APPROACH: In vivo spinal electrophysiological assays in anaesthetized rats were used to determine the effects of spinal administration of JZL184 on spinal nociceptive processing in the presence and absence of hindpaw inflammation. Contributions of CB(1) receptors to these effects was assessed with AM251. Inhibition of 2-oleoylglycerol hydrolytic activity and alterations of 2-AG in the spinal cord after JZL 184 were also assessed. KEY RESULTS: Spinal JZL184 dose-dependently inhibited mechanically evoked responses of wide dynamic range (WDR) neurones in naïve anaesthetized rats, in part via the CB(1) receptor. A single spinal administration of JZL184 abolished inflammation-induced expansion of the receptive fields of spinal WDR neurones. However, neither spinal nor systemic JZL184 altered levels of 2-AG, or 2-oleoylglycerol hydrolytic activity in the spinal cord, although JZL184 displayed robust inhibition of MAGL when incubated with spinal cord tissue in vitro. CONCLUSIONS AND IMPLICATIONS: JZL184 exerted robust anti-nociceptive effects at the level of the spinal cord in vivo and inhibited rat spinal cord MAGL activity in vitro. The discordance between in vivo and in vitro assays suggests that localized sites of action of JZL184 produce these profound functional inhibitory effects. LINKED ARTICLES: This article is part of a themed section on Cannabinoids. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.167.issue-8.

So what do we call GPR18 now?

The further characterization of the orphan GPCR GPR18 conducted by McHugh et al. in this issue of the British Journal of Pharmacology has generated a pharmacological profile that raises some interesting questions about the nomenclature of this receptor and may also prompt some questions about the pharmacological definition of the classical cannabinoid receptors, CB(1) and CB(2) . LINKED ARTICLES This article is a commentary on McHugh et al., pp. 2414-2424 of this issue and is part of a themed section on Cannabinoids in Biology and Medicine. To view McHugh et al. visit http://dx.doi.org/10.1111/j.1476-5381.2011.01497.x. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

International Union of Basic and Clinical Pharmacology. LXXIX. Cannabinoid receptors and their ligands: beyond CB1 and CB2.

There are at least two types of cannabinoid receptors (CB(1) and CB(2)). Ligands activating these G protein-coupled receptors (GPCRs) include the phytocannabinoid Δ(9)-tetrahydrocannabinol, numerous synthetic compounds, and endogenous compounds known as endocannabinoids. Cannabinoid receptor antagonists have also been developed. Some of these ligands activate or block one type of cannabinoid receptor more potently than the other type. This review summarizes current data indicating the extent to which cannabinoid receptor ligands undergo orthosteric or allosteric interactions with non-CB(1), non-CB(2) established GPCRs, deorphanized receptors such as GPR55, ligand-gated ion channels, transient receptor potential (TRP) channels, and other ion channels or peroxisome proliferator-activated nuclear receptors. From these data, it is clear that some ligands that interact similarly with CB(1) and/or CB(2) receptors are likely to display significantly different pharmacological profiles. The review also lists some criteria that any novel "CB(3)" cannabinoid receptor or channel should fulfil and concludes that these criteria are not currently met by any non-CB(1), non-CB(2) pharmacological receptor or channel. However, it does identify certain pharmacological targets that should be investigated further as potential CB(3) receptors or channels. These include TRP vanilloid 1, which possibly functions as an ionotropic cannabinoid receptor under physiological and/or pathological conditions, and some deorphanized GPCRs. Also discussed are 1) the ability of CB(1) receptors to form heteromeric complexes with certain other GPCRs, 2) phylogenetic relationships that exist between CB(1)/CB(2) receptors and other GPCRs, 3) evidence for the existence of several as-yet-uncharacterized non-CB(1), non-CB(2) cannabinoid receptors; and 4) current cannabinoid receptor nomenclature.

Vasorelaxation to N-oleoylethanolamine in rat isolated arteries: mechanisms of action and modulation via cyclooxygenase activity.

BACKGROUND AND PURPOSE: The endocannabinoid-like molecule N-oleoylethanolamine (OEA) is found in the small intestine and regulates food intake and promotes weight loss. The principal aim of the present study was to evaluate the vascular effects of OEA. EXPERIMENTAL APPROACH: Perfused isolated mesenteric arterial beds were pre-contracted with methoxamine or high potassium buffers and concentration-response curves to OEA were constructed. Combinations of inhibitors to block nitric oxide production, sensory nerve activity, cyclooxygenase activity, potassium channels, chloride channels and gap junctions, and a cannabinoid CB(1) receptor antagonist, were used during these experiments. The effects of OEA on caffeine-induced contractions in calcium-free buffer were also assessed. Isolated thoracic aortic rings were used as a comparison. KEY RESULTS: OEA caused concentration-dependent vasorelaxation in rat isolated mesenteric arterial beds and thoracic aortic rings, with a greater maximal response in mesenteric vessels. This relaxation was sensitive to inhibition of sensory nerve activity and endothelial removal in both preparations. The cyclooxygenase inhibitor indomethacin reversed the effects of capsaicin pre-treatment in perfused mesenteric arterial beds and indomethacin alone enhanced vasorelaxation to OEA. The OEA-induced vasorelaxation was inhibited by a CB(1) receptor antagonist only in aortic rings. In mesenteric arteries, OEA suppressed caffeine-induced contractions in calcium-free buffer. CONCLUSIONS AND IMPLICATIONS: The vasorelaxant effects of OEA are partly dependent on sensory nerve activity and a functional endothelium in the vasculature. In addition, vasorelaxation to OEA is enhanced following cyclooxygenase inhibition. OEA may also interfere with the release of intracellular calcium in arterial preparations.

Serial batch leaching procedure for characterization of coal fly ash.

Although many leaching methods have been used for various purposes by research groups, industries, and regulators, there is still a need for a simple but comprehensive approach to leaching coal utilization by-products and other granular materials in order to estimate potential release of heavy metals when these materials are exposed to natural fluids. A serial batch characterization method has been developed at the National Energy Technology Laboratory that can be completed in 2-3 days to serve as a screening tool. The procedure provides an estimate of cumulative metals release under varying pH conditions, and leaching the sample at increasing liquid/solid ratios can indicate the rate at which this process will occur. This method was applied to eight fly ashes, adapted to the acidic or alkaline nature of the ash. The leachates were analyzed for 30 elements. The test was run in quadruplicate, and the relative standard deviation (RSD) was used as a measure of method reproducibility. RSD values are between 0.02 and 0.70, with the majority of the RSD values less than 0.3. The serial batch leaching procedure was developed as a simple, relatively quick, yet comprehensive method of estimating the risk of heavy metal release from fly ash when it is exposed to natural fluids, such as acid rain or groundwater. Tests on a random selection of coal fly ashes have shown it to be a reasonably precise method for estimating the availability and long-term release of cations from fly ash.

Effect of inhibition of extracellular signal-regulated kinase on relaxations to beta-adrenoceptor agonists in porcine isolated blood vessels.

BACKGROUND AND PURPOSE: Stimulation of vascular beta-adrenoceptors causes vasodilatation through activation of adenylyl cyclase (AC) and plasma membrane potassium channels, and beta-adrenoceptors have been linked to activation of extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase in various cell lines. However, how these findings relate to functional responses in intact tissues is largely unknown. The aim of this study, therefore, was to investigate the role of ERK in beta-adrenoceptor-induced vasodilatation. EXPERIMENTAL APPROACH: Segments of porcine coronary artery were mounted in a Mulvany wire myograph and bathed in Krebs-Henseleit buffer gassed with 95% O(2)/5% CO(2) and maintained at 37 degrees C. Tissues were pre-contracted with the thromboxane mimetic U46619, endothelin-1 or KCl. Cumulative concentration-response curves to beta-adrenoceptor agonists or forskolin were then carried out in the absence or presence of the mitogen-activated protein kinase kinase (MEK) inhibitors PD98059 (10 or 50 microM) or U0126 (10 microM). KEY RESULTS: PD98059 caused a concentration-dependent leftward shift in response to isoprenaline (pEC(50) control, 7.5 +/- 0.1; 50 microM PD98059, 8.1 +/- 0.1: P < 0.05). Inhibition of MEK also enhanced the maximum relaxation seen with salbutamol, but not the responses to the beta(1)-adrenoceptor selective agonist xamoterol or the AC activator forskolin. There was no enhancement of the relaxations to beta-adrenoceptor agonists after inhibition of ERK activation in tissues pre-contracted with KCl or treated with the K(+) channel blocker tetraethylammonium. CONCLUSIONS AND IMPLICATIONS: These data indicate that ERK inhibits beta(2)-adrenoceptor-mediated vasodilatation through a mechanism which may involve inactivation of plasma membrane potassium channels.

Agonist-occupied A3 adenosine receptors exist within heterogeneous complexes in membrane microdomains of individual living cells.

G protein-coupled receptors are known to be organized within different membrane compartments or microdomains of individual cells. Here, we have used a fluorescent A3 adenosine receptor (A3-AR) agonist, ABEA-X-BY630, and the technique of fluorescence correlation spectroscopy (FCS) to investigate the diffusional characteristics of functional agonist-occupied A3-AR complexes in single living cells. In Chinese hamster ovary cells expressing the human A3-AR, the fluorescent A3-AR agonist was able to inhibit forskolin-stimulated [3H]cAMP production (pEC50=8.57), and this was antagonized by the A3-selective antagonist MRS1220 (pK(B)=9.32). The fluorescent ligand also stimulated phosphoinositide hydrolysis (pEC50=7.34). Ligand binding to the A3-AR on the membranes of single cells and subsequent increases in single cell [Ca2+]i were monitored simultaneously in real time using confocal microscopy. FCS measurements in small-membrane microdomains (approximately 0.2 microm2) revealed two agonist-occupied A3-AR components with differing diffusion characteristics (diffusion coefficients=2.65x10(-8) and 1.19x10(-9) cm2/s, respectively). The binding of ligand to these two components was reduced from 5.1 and 14.9 to 2.6 and 3.3 receptors/microm2, respectively, by MRS1220 (100 nM). These data provide direct evidence for at least two populations of agonist-occupied A3-receptor complexes, showing different motilities within the membrane of single living cells.

Cannabinoid activation of PPAR alpha; a novel neuroprotective mechanism.

BACKGROUND AND PURPOSE: Although CB(1) receptor activation evokes neuroprotection in response to cannabinoids, some cannabinoids have been reported to be peroxisome proliferator activated receptor (PPAR) ligands, offering an alternative protective mechanism. We have, therefore, investigated the ability of a range of cannabinoids to activate PPAR alpha and for N-oleoylethanolamine (OEA), an endogenous cannabinoid-like compound (ECL), to evoke neuroprotection. EXPERIMENTAL APPROACH: Assays of PPAR alpha occupancy and gene transactivation potential were conducted in cell-free and transfected HeLa cell preparations, respectively. In vivo estimates of PPAR alpha activation through fat mobilization and gene transcription were conducted in mice. Neuroprotection in vivo was investigated in wild-type and PPAR alpha gene-disrupted mice. KEY RESULTS: The ECLs OEA, anandamide, noladin ether and virodhamine were found to bind to the purified PPAR alpha ligand binding domain and to increase PPAR alpha-driven transcriptional activity. The high affinity synthetic CB(1/2) cannabinoid agonist WIN 55212-2 bound to PPAR alpha equipotently with the PPARalpha agonist fenofibrate, and stimulated PPARalpha-mediated gene transcription. The phytocannabinoid delta 9 tetrahydrocannabinol was without effect. OEA and WIN 55212-2 induced lipolysis in vivo, while OEA pre-treatment reduced infarct volume from middle cerebral artery occlusion in wild-type, but not in PPAR alpha-null mice. OEA treatment also led to increased expression of the NFkappa B-inhibitory protein, Ikappa B, in mouse cerebral cortex, while expression of the NFkappa B-regulated protein COX-2 was inhibited. CONCLUSIONS AND IMPLICATIONS: These data demonstrate the potential for a range of cannabinoid compounds, of diverse structures, to activate PPAR alpha and suggest that at least some of the neuroprotective properties of these agents could be mediated by nuclear receptor activation.