β2AR Activation Research Articles

Pharmacogenomics of β-Adrenergic Receptor Physiology and Response to β-Blockade

Myocardial β-adrenergic receptors (βARs) are important in altering heart rate, inotropic state, and myocardial relaxation (lusitropy). The β1AR and β2AR stimulation increases cyclic adenosine monophosphate concentration with the net result of myocyte contraction, whereas β3AR stimulation results in decreased inotropy. Downregulation of β1ARs in heart failure, as well as an increased β3AR activity and density, lead to decreased cyclic adenosine monophosphate production and reduced inotropy. The βAR antagonists are commonly used in patients with coronary artery disease and heart failure; however, perioperative use of βAR antagonists is controversial. Individual patient's response to beta-blocker therapy is an area of intensive research, and apart from pharmacokinetics, pharmacodynamics, and ethnic differences, genetic alterations have become more important in the last 20 years. The most common genetic variants in humans are single nucleotide polymorphisms (SNPs). There are 2 clinically relevant SNPs for the β1AR (Ser49Gly, Arg389Gly), 3 for the β2AR (Arg16Gly, Gln27Glu, Thr164Ile), and 1 for the β3AR (Trp64Arg). Although results are somewhat controversial, generally large datasets have the potential to show a relationship between βAR SNPs and outcomes such as development and progression of heart failure, coronary artery disease, vascular reactivity, hypertension, asthma, obesity, and diabetes. Although βAR SNPs may not directly cause disease, they appear to be risk factors for, and modifiers of, disease and the response to stress and drugs. In the perioperative setting, this has specifically been demonstrated for the Arg389Gly β1AR polymorphism with which patients with the Gly variant had a higher incidence of adverse perioperative events. Knowing that genetic variants play an important role, perioperative medicine will likely change from simple therapeutic intervention to a more personalized way of adrenergic receptor modulation.

Activation of β‐adrenergic receptors facilitates heterosynaptic translation‐dependent long‐term potentiation

Noradrenaline critically modulates the ability of synapses to undergo long-term plasticity on time scales extending well beyond fast synaptic transmission. Noradrenergic signalling through β-adrenergic receptors (β-ARs) enhances memory consolidation and can boost the longevity of long-term potentiation (LTP). Previous research has shown that stimulation of one synaptic pathway with a protocol that induces persistent, translation-dependent LTP can enable the induction of LTP by subthreshold stimulation at a second, independent synaptic pathway. This heterosynaptic facilitation depends on the regulation and synthesis of proteins. Recordings taken from area CA1 in mouse hippocampal slices showed that induction of β-AR-dependent LTP at one synaptic pathway (S1) can facilitate LTP at a second, independent pathway (S2) when low-frequency, subthreshold stimulation is applied after a 30 min delay. β-AR-dependent heterosynaptic facilitation requires protein synthesis as inhibition of mammalian target of rapamycin (mTOR), extracellular signal-regulated kinase (ERK), or translation, prevented homo- and heterosynaptic LTP. Shifting application of a translational repressor, emetine, to coincide with S2 stimulation did not block LTP. Heterosynaptic LTP was prevented in the presence of the cell-permeable cAMP-dependent protein kinase inhibitor, PKI. Conversely, the time window for inter-pathway transfer of heterosynaptic LTP was extended through inhibition of GluR2 endocytosis. Our data show that activation of β-ARs boosts the heterosynaptic expression of translation-dependent LTP. These results suggest that engagement of the noradrenergic system may extend the associative capacity of hippocampal synapses through facilitation of intersynaptic crosstalk.

β-arrestin2 mediates β-2 adrenergic receptor signaling inducing prostate cancer cell progression

The expression of the β-2 adrenergic receptor (β2AR), one of the stress-inducible receptors, has been reported to be closely correlated with malignant tumors. Prostate cancer is the most common non-cutaneous cancer among males, accompanied with increased castration levels and β2AR activation in patients. However, the role of β2AR activation in prostate cancer cells and its underlying mechanisms are not fully understood. Here, we found that β2AR activation promoted cell proliferation and cell migration through increasing cellular adenylyl cyclase (cAMP) levels and ERK1/2 activation in LNCaP and PC3 prostate cancer cells. Moreover, the scaffold protein β-arrestin2 was found to be involved in the β2AR-mediated activation of ERK1/2 and cell proliferation using stable overexpressing β-arrestin2 LNCaP (LNCaP-βArr2) cells. Furthermore, enhanced β-arrestin2/c-Src complex formation by β2AR activation was observed in LNCaP-βArr2 cells. In addition, the c-Src inhibitor could block this enhanced complex formation and suppressed cell proliferation. This study demonstrates that βArr2 is involved in prostate carcinogenesis induced by stress and provides potential therapeutic targets for cancer.

β-Adrenergic Inhibition of Contractility in L6 Skeletal Muscle Cells

The β-adrenoceptors (β-ARs) control many cellular processes. Here, we show that β-ARs inhibit calcium depletion-induced cell contractility and subsequent cell detachment of L6 skeletal muscle cells. The mechanism underlying the cell detachment inhibition was studied by using a quantitative cell detachment assay. We demonstrate that cell detachment induced by depletion of extracellular calcium is due to myosin- and ROCK-dependent contractility. The β-AR inhibition of L6 skeletal muscle cell detachment was shown to be mediated by the β2-AR and increased cAMP but was surprisingly not dependent on the classical downstream effectors PKA or Epac, nor was it dependent on PKG, PI3K or PKC. However, inhibition of potassium channels blocks the β2-AR mediated effects. Furthermore, activation of potassium channels fully mimicked the results of β2-AR activation. In conclusion, we present a novel finding that β2-AR signaling inhibits contractility and thus cell detachment in L6 skeletal muscle cells by a cAMP and potassium channel dependent mechanism.

Caveolae compartmentalise β2-adrenoceptor signals by curtailing cAMP production and maintaining phosphatase activity in the sarcoplasmic reticulum of the adult ventricular myocyte

Inotropy and lusitropy in the ventricular myocyte can be efficiently induced by activation of β1-, but not β2-, adrenoceptors (ARs). Compartmentation of β2-AR-derived cAMP-dependent signalling underlies this functional discrepancy. Here we investigate the mechanism by which caveolae (specialised sarcolemmal invaginations rich in cholesterol and caveolin-3) contribute to compartmentation in the adult rat ventricular myocyte. Selective activation of β2-ARs (with zinterol/CGP20712A) produced little contractile response in control cells but pronounced inotropic and lusitropic responses in cells treated with the cholesterol-depleting agent methyl-β-cyclodextrin (MBCD). This was not linked to modulation of L-type Ca2+ current, but instead to a discrete PKA-mediated phosphorylation of phospholamban at Ser16. Application of a cell-permeable inhibitor of caveolin-3 scaffolding interactions mimicked the effect of MBCD on phosphorylated phospholamban (pPLB) during β2-AR stimulation, consistent with MBCD acting via caveolae. Biosensor experiments revealed β2-AR mobilisation of cAMP in PKA II signalling domains of intact cells only after MBCD treatment, providing a real-time demonstration of cAMP freed from caveolar constraint. Other proteins have roles in compartmentation, so the effects of phosphodiesterase (PDE), protein phosphatase (PP) and phosphoinositide-3-kinase (PI3K) inhibitors on pPLB and contraction were compared in control and MBCD treated cells. PP inhibition alone was conspicuous in showing robust de-compartmentation of β2-AR-derived signalling in control cells and a comparatively diminutive effect after cholesterol depletion. Collating all evidence, we promote the novel concept that caveolae limit β2-AR-cAMP signalling by providing a platform that not only attenuates production of cAMP but also prevents inhibitory modulation of PPs at the sarcoplasmic reticulum. This article is part of a Special Issue entitled “Local Signaling in Myocytes”.

Regulation of contractility and metabolic signaling by the β2-adrenergic receptor in rat ventricular muscle

AimsCardiac function is modulated by the sympathetic nervous system through β-adrenergic receptor (β-AR) activity and this represents the main regulatory mechanism for cardiac performance. To date, however, the metabolic and molecular responses to β2-agonists are not well characterized. Therefore, we studied the inotropic effect and signaling response to selective β2-AR activation by tulobuterol. Main methodsStrips of rat right ventricle were electrically stimulated (1Hz) in standard Tyrode solution (95% O2, 5% CO2) in the presence of the β1-antagonist CGP-20712A (1μM). A cumulative dose–response curve for tulobuterol (0.1–10μM), in the presence or absence of the phosphodiesterase (PDE) inhibitor IBMX (30μM), or 10min incubation (1μM) with the β2-agonist tulobuterol was performed. Key findingsβ2-AR stimulation induced a positive inotropic effect (maximal effect=33±3.3%) and a decrease in the time required for half relaxation (from 45±0.6 to 31±1.8ms, −30%, p<0.001) after the inhibition of PDEs. After 10min of β2-AR stimulation, p-AMPKαT172 (54%), p-PKBT308 (38%), p-AS160T642 (46%) and p-CREBS133 (63%) increased, without any change in p-PKAT197. SignificanceThese results suggest that the regulation of ventricular contractility is not the primary function of the β2-AR. Rather, β2-AR could function to activate PKB and AMPK signaling, thereby modulating muscle mass and energetic metabolism of rat ventricular muscle.

β2-Adrenergic Receptor Genotype and Other Variables that Contribute to Labor Pain and Progress

β2-Adrenergic receptor (β2AR) activity influences labor. Its genotype affects the incidence of preterm delivery. We determined the effect of β2AR genotype on term labor progress and maternal pain. We prospectively enrolled 150 nulliparous parturients in the third trimester and obtained sensory thresholds, demographic information, and DNA. Cervical dilation, pain scores, and labor management data were extracted with associated times. The association of genetic and demographic factors with labor was tested using mixed effects models. Parturients who express Gln at the 27 position of the β2AR had slower labor (P < 0.03). They progressed from 1-10 cm dilation in approximately 21 h compared with 14 h among other patients. Asian ethnicity, previously associated with slower labor, is highly associated with this polymorphism (P < 0.0001). Heavier and black patients had slower latent labor (P < 0.01, 0.01). Neuraxial analgesia was associated with slower labor progress (P < 0.0001). It could take up to 36 h for parturients who were black and/or more than median weight (165 lb) to transition from 1 cm cervical dilation to active labor. However, after this active phase began, labor rates among these patients were similar to that of other parturients. We detected a strong association between β2AR genotype and slower labor. Asian ethnicity may be a proxy for β2AR genotype. Black women and those of higher than average weight have slower latent labor. These results confirm many of the associations found when this mathematical model was applied to a large retrospective cohort, further validating this approach to description and analysis of labor progress.

Activation of beta3 adrenoreceptors decreases the amplitude of the electrical field stimulation induced contractions in rat detrusor smooth muscle isolated strips

It is believed that during bladder filling phase, β-adrenoceptors (β-AR) facilitate relaxation of the detrusor smooth muscle (DSM). Our previous studies showed that BRL37344, a specific β3-AR agonist, caused a concentration-dependant decrease in the myogenic contractions of rat isolated DSM strips. Here, using tissue baths equipped with electrodes for electrical field stimulation (EFS), we investigated the role of β3-AR in rat DSM neurogenic contractions. Neurogenic contractions were generated by EFS pulses (20 V amplitude, 0.75 ms width, and 3 s duration) with increasing frequencies (0.5–50 Hz). BRL37344 (100 μM) significantly decreased the amplitude of the EFS-induced contractions of rat DSM (n=12, N=6). We further used specific inhibitors to separate the cholinergic and purinergic components of the EFS-induced contractions of rat DSM. The BRL37344 inhibitory effect was also observed in the presence of 1 μM atropine (n=15, N=8) as well as in the presence of 10 μM suramin and 10 μM α,β-methylene-ATP (n=13, N=5). BRL37344 (100 μM) inhibitory effect was blocked by SR59230A (10 μM), a specific β3-AR antagonist (n=8, N=3). SR59230A per se did not have any effect on the neurogenic contractions (n=8, N=3). In conclusion, activation of β3-AR decreases DSM neurogenic contractions, thus making β3-AR a new pharmacological target for the treatment of overactive bladder.

A Homogeneous Single-Label Time-Resolved Fluorescence cAMP Assay

G-protein-coupled receptors (GPCRs) are an important class of pharmaceutical drug targets. Functional high-throughput GPCR assays are needed to test an increasing number of synthesized novel drug compounds and their function in signal transduction processes. Measurement of changes in the cyclic adenosine monophosphate (cAMP) concentration is a widely used method to verify GPCR activation in the adenylyl cyclase pathway. Here, a single-label time-resolved fluorescence and high-throughput screening (HTS)-feasible method was developed to measure changes in cAMP levels in HEK293(i) cells overexpressing either β(2)-adrenergic or δ-opioid receptors. In the quenching resonance energy transfer (QRET) technique, soluble quenchers reduce the signal of unbound europium(III)-labeled cAMP in solution, whereas the antibody-bound fraction is fluorescent. The feasibility of this homogeneous competitive assay was proven by agonist-mediated stimulation of receptors coupled to either the stimulatory G(s) or inhibitory G(i) proteins. The reproducibility of the assays was excellent, and Z' values exceeded 0.7. The dynamic range, signal-to-background ratio, and detection limit were compared with a commercial time-resolved fluorescence resonance energy transfer (TR-FRET) assay. In both homogeneous assays, similar assay parameters were obtained when adenylyl cyclase was stimulated directly by forskolin or via agonist-mediated activation of the G(s)-coupled β(2)AR. The advantage of using the single-label approach relates to the cost-effectiveness of the QRET system compared with the two-label TR-FRET assay as there is no need for labeling of two binding partners leading to reduced requirements for assay optimization.

Inhibition of Protein Phosphatase 2A Activity by PI3Kγ Regulates β-Adrenergic Receptor Function

Phosphoinositide 3-kinase γ (PI3Kγ) is activated by Gprotein-coupled receptors (GPCRs). We show here that PI3Kγ inhibits protein phosphatase 2A (PP2A) at the β-adrenergic receptor (βAR, a GPCR) complex altering G protein coupling. PI3Kγ inhibition results in significant increase of βAR-associated phosphatase activity leading to receptor dephosphorylation and resensitization preserving cardiac function. Mechanistically, PI3Kγ inhibits PP2A activity at the βAR complex by phosphorylating an intracellular inhibitor of PP2A (I2PP2A) on serine residues 9 and 93, resulting in enhanced binding to PP2A. Indeed, enhanced phosphorylation of β2ARs is observed with a phosphomimetic I2PP2A mutant that was completely reversed with a mutant mimicking dephosphorylated state. siRNA depletion of endogenous I2PP2A augments PP2A activity despite active PI3K resulting in β2AR dephosphorylation and sustained signaling. Our study provides the underpinnings of a PI3Kγ-mediated regulation of PP2A activity that has significant consequences on receptor function with broad implications in cellular signaling.

Transient β2-Adrenoceptor Activation Confers Pregnancy Loss by Disrupting Embryo Spacing at Implantation

Pregnancy loss is a serious social and medical issue, with one important cause associated with aberrant embryo implantation during early pregnancy. However, whether and how the process of embryo implantation is affected by environmental factors such as stress-induced sympathetic activation remained elusive. Here we report an unexpected, transient effect of β2-adrenoreceptor (β2-AR) activation (day 4 postcoitus) in disrupting embryo spacing at implantation, leading to substantially increased midterm pregnancy loss. The abnormal embryo spacing could be prevented by pretreatment of β2-AR antagonist or genetic ablation of β-AR. Similar β2-AR activation at day 5 postcoitus, when implantation sites have been established, did not affect embryo spacing or pregnancy outcome, indicating that the adverse effect of β2-AR activation is limited to the preimplantation period before embryo attachment. In vitro and in vivo studies demonstrated that the transient β2-AR activation abolished normal preimplantation uterine contractility without adversely affecting blastocyst quality. The contractility inhibition is mediated by activation of the cAMP-PKA pathway and accompanied by specific down-regulation of lpa3, a gene previously found to be critical for uterine contraction and embryo spacing. These results indicated that normal uterine contraction-mediated correct intrauterine embryo distribution is crucial for successful ongoing pregnancy. Abnormal β2-AR activation at early pregnancy provided a molecular clue in explaining how maternal stress at early stages could adversely affect the pregnancy outcome.

Effects of Cholesterol Depletion on Compartmentalized cAMP Responses in Adult Cardiac Myocytes

The role of cholesterol-dependent lipid rafts in producing compartmentalized responses of β1-adrenergic receptors (β1ARs) and E-type prostaglandin receptors (EPRs) was investigated in adult rat ventricular myocytes. β1ARs were found in lipid raft and non-lipid raft containing membrane fractions, while EPRs were only found in non-lipid raft fractions. Furthermore, β1AR activation enhanced the L-type Ca2+ current (ICa-L), intracellular Ca2+ [Ca2+]i transient, and myocyte shortening, while EPR activation had no effect. Cholesterol depletion by treatment with methyl-β-cyclodextrin (MβCD) did not eliminate compartmentalized behavior but significantly enhanced the sensitivity of functional responses produced by β1ARs. In MβCD-treated cells, 1 nM isoproterenol increased ICa-L by 49 +/- 8.3% (n = 5) as compared to 15 +/- 5% (n = 13) in control cells. These responses were blocked by the specific β1AR antagonist, 100 nM CGP20712A. Similarly, β1AR activation led to an increase in cell shortening and [Ca2+]i transient from 63 +/- 13% and 18 +/- 4.1% in control cells (n = 17) to 188 +/- 19.5% and 35 +/- 4.3% in MβCD-treated cells (n = 22) respectively. Cholesterol depletion failed to elicit any effect on EPR activation. Changes in cAMP activity were also measured in intact cells using two different FRET-based biosensors: a type II PKA-based probe to monitor cAMP in subcellular compartment that include caveolar lipid raft microdomains and a freely diffusible Epac2-based probe. β1AR and EPR activation elicited responses detected by both FRET probes. However, cholesterol depletion only affected β1AR responses detected by the PKA probe. These results indicate that caveolar lipid rafts alone are not sufficient to explain the differences between β1AR and EPR responses. They also suggest that β1AR regulation of myocyte contraction involves the local production of cAMP by a subpopulation of receptors associated with lipid rafts.

β-Adrenergic receptors (β-AR) regulate VEGF and IL-6 production by divergent pathways in high β-AR-expressing breast cancer cell lines

Activation of β-adrenergic receptors (β-AR) drives proangiogenic factor production in several types of cancers. To examine β-AR regulation of breast cancer pathogenesis, β-AR density, signaling capacity, and functional responses to β-AR stimulation were studied in four human breast adenocarcinoma cell lines. β-AR density ranged from very low in MCF7 and MB-361 to very high in MB-231 and in a brain-seeking variant of MB-231, MB-231BR. Consistent with β-AR density, β-AR activation elevated cAMP in MCF7 and MB-361 much less than in MB-231 and MB-231BR. Functionally, β-AR stimulation did not markedly alter vascular endothelial growth factor (VEGF) production by MCF7 or MB-361. In the two high β-AR-expressing cell lines MB-231 and MB-231BR, β-AR-induced cAMP and VEGF production differed considerably, despite similar β-AR density. The β(2)-AR-selective agonist terbutaline and the endogenous neurotransmitter norepinephrine decreased VEGF production by MB-231, but increased VEGF production by MB-231BR. Moreover, β(2)-AR activation increased IL-6 production by both MB-231 and MB-231BR. These functional alterations were driven by elevated cAMP, as direct activation of adenylate cyclase by forskolin elicited similar alterations in VEGF and IL-6 production. The protein kinase A antagonist KT5720 prevented β-AR-induced alterations in MB-231 and MB-231BR VEGF production, but not IL-6 production. Conclusions β-AR expression and signaling is heterogeneous in human breast cancer cell lines. In cells with high β-AR density, β-AR stimulation regulates VEGF production through the classical β-AR-cAMP-PKA pathway, but this pathway can elicit directionally opposite outcomes. Furthermore, in the same cells, β-AR activate a cAMP-dependent, PKA-independent pathway to increase IL-6 production. The complexity of breast cancer cell β-AR expression and functional responses must be taken into account when considering β-AR as a therapeutic target for breast cancer treatment.

The Role of β-adrenergic Receptors in the Cardioprotective Effects of Beta-Preconditioning (βPC)

To determine the mechanism whereby transient stimulation of the β-adrenergic receptor subtypes (β-AR) elicit cardioprotection against subsequent ischaemia. Isolated rat hearts were subjected to 35 min regional ischaemia (RI) and reperfusion and infarct size (IS) determined. Hearts were preconditioned with 5 min isoproterenol (β1/β2-AR agonist), denopamine (β1-AR agonist), formoterol hemifumarate (β2-AR agonist) or BRL37344 (β3-AR agonist) and 5 min reperfusion. The roles of the β-ARs, NO, PKA, and PI3-K were explored by using selective antagonists/blockers. Pertussis toxin was administered i.p., 48 h prior to experimentation. IS of hearts preconditioned with either isoproterenol, denopamine or formoterol (% of area at risk: 23.6 ± 1.26; 24.52 ± 0.89; 20.74 ± 0.85 respectively) were significantly smaller than that of non-preconditioned hearts (41.7 ± 1.65) and associated with improvement in postischaemic mechanical performance. The β3-AR agonist BRL37344 could not reduce IS. The β1- and β2-AR blockers CGP-20712A and ICI-118551 abolished the reduction in IS and improvement in mechanical recovery during reperfusion induced by isoproterenol preconditioning, while the β3-AR blocker SR59230A was without effect. Both Rp-8-CPT-cAMPs and wortmannin significantly increased IS when administered before and during β1/β2-AR preconditioning and reduced mechanical recovery. PTX pretreatment had no significant effect on the reduction in IS induced by β1/β2-AR or β2-AR preconditioning, but reduced mechanical recovery in β2-AR preconditioning. Similarly the NOS inhibitors L-NAME and LNNA had no effect on IS in β1/β2-AR preconditioning, but depressed mechanical recovery. Protection afforded by β-ARs stimulation, depends on activation of both β1-AR and β2-ARs but not β3-AR. With functional recovery as endpoint, results suggest involvement of NO in β1/β2-AR preconditioning and the Gi protein in β2-AR preconditioning. Both PKA and PI3-K activation were essential for β1/β2-AR cardioprotection.

過活動膀胱（Ｏｖｅｒａｃｔｉｖｅ Ｂｌａｄｄｅｒ）治療薬を指向した選択的β３アドレナリン受容体（β３‐ＡＲ）アゴニストの創製

β-Adrenoceptors (β-ARs) are classified into three types; β1-, β2-, and β3-ARs. In humans, the detrusor muscle has recently been reported to be the predominant site of β3-AR mRNA expression. The relaxation induced by adrenergic stimulation of the human detrusor is mediated mainly through β3-AR activation, suggesting that β3-adrenergic receptor agonists may represent as potential drugs for treating overactive bladder (OAB). In this paper, we described that the synthesis and discovery of novel class of biphenyl analogues containing an carboxylic acid moiety and acylsulfonamide, which has been identified highly potent and selective human β3-AR agonists with good oral bioavailability. We also described scalable process for our clinical candidate of FK4664 and AS1714955. Furthermore, in a metabolism study of benzoic acid analogues conducted in human hepatocytes, we identified an acylglucuronide conjugated metabolite (M-2), and the M-2 metabolite of FK4664 was prepared with high selectivity.

Possible Involvement of β1 Receptors in Various Emetogen-Induced Increases in Salivary Amylase Activity in Rats

We investigated the inhibitory effects of β1- or β2-adrenoceptor (AR) antagonists on salivary amylase secretion produced by various emetic agents, such as cisplatin, apomorphine, and lithium chloride (LiCl), or the non-emetic agent β1/2-AR agonist isoprenaline in rats. We also determined the inhibitory effect of metoclopramide, a dopamine D2–receptor antagonist, on increases in the salivary amylase activity induced by apomorphine or granisetron, a 5-HT3–receptor antagonist, on LiCl-induced increased salivary amylase activity. Isoprenaline (0.01 mg/kg, s.c.) produced an increase in salivary amylase and the increase was inhibited by the β1/2-AR antagonist propranolol (5 mg/kg, s.c.) and β1-AR antagonist atenolol (2 mg/kg, s.c.) but not by the β2-AR antagonist butoxamine (8 mg/kg, s.c.). The increased amylase activity induced by cisplatin (15 mg/kg, i.v.), apomorphine (3 mg/kg, s.c.), or LiCl (120 mg/kg, i.p.) was inhibited significantly by atenolol (2 mg/kg, s.c.) but not by butoxamine (8 mg/kg, s.c.). In addition, increases in amylase activities induced by apomorphine and LiCl were inhibited significantly by metoclopramide (10 mg/kg, i.v.) and granisetron (3 mg/kg, i.v.), respectively. These results suggest that salivary amylase secretion induced by various emetogens is involved in β1-adrenoceptor activity and that salivary amylase activity is useful to detect emetogens with no direct β1-AR activation in rats, a species that does not exhibit vomiting.

β 3 Adrenergic Stimulation of the Cardiac Na + -K + Pump by Reversal of an Inhibitory Oxidative Modification

inhibition of L-type Ca(2+) current contributes to negative inotropy of β(3) adrenergic receptor (β(3) AR) activation, but effects on other determinants of excitation-contraction coupling are not known. Of these, the Na(+)-K(+) pump is of particular interest because of adverse effects attributed to high cardiac myocyte Na(+) levels and upregulation of the β(3) AR in heart failure. we voltage clamped rabbit ventricular myocytes and identified electrogenic Na(+)-K(+) pump current (I(p)) as the shift in holding current induced by ouabain. The synthetic β(3) AR agonists BRL37344 and CL316,243 and the natural agonist norepinephrine increased I(p). Pump stimulation was insensitive to the β(1)/β(2) AR antagonist nadolol and the protein kinase A inhibitor H-89 but sensitive to the β(3) AR antagonist L-748,337. Blockade of nitric oxide synthase abolished pump stimulation and an increase in fluorescence of myocytes loaded with a nitric oxide-sensitive dye. Exposure of myocytes to β(3) AR agonists decreased β(1) Na(+)-K(+) pump subunit glutathionylation, an oxidative modification that causes pump inhibition. The in vivo relevance of this was indicated by an increase in myocardial β(1) pump subunit glutathionylation with elimination of β(3) AR-mediated signaling in β(3) AR(-/-) mice. The in vivo effect of BRL37344 on contractility of the nonfailing and failing heart in sheep was consistent with a beneficial effect of Na(+)-K(+) pump stimulation in heart failure. the β(3) AR mediates decreased β(1) subunit glutathionylation and Na(+)-K(+) pump stimulation in the heart. Upregulation of the receptor in heart failure may be a beneficial mechanism that facilitates the export of excess Na(+).

Evolving Concepts Concerning Cardiac &amp;#946;-Adrenoceptor Function in Heart Failure

This review describes the clinical application of β-adrenergic blocking drugs over time in patients with congestive heart failure. The different pharmacological properties of these drugs in relation to clinical outcomes raises questions as to their optimal desirable profile based on studies showing the undesirable effects of excessive β(2)-AR activation. The rationale for the use of selective β(2)-AR antagonists in heart failure is discussed.

Effect of exercise intensity and AICAR on isoform-specific expressions of murine skeletal muscle PGC-1α mRNA: a role of β2-adrenergic receptor activation

There are three isoforms of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) mRNA, which promotes mitochondrial biogenesis in skeletal muscles. Compared with PGC-1α-a mRNA, PGC-1α-b or PGC-1α-c mRNA is transcribed by a different exon 1 of the PGC-1α gene. In this study, effects of exercise intensity and 5-aminoimidazole-4-carboxamide-1β-d-ribofuranoside (AICAR) on isoform-specific expressions of PGC-1α were investigated. All isoforms were increased in proportion to exercise intensity of treadmill running (10-30 m/min for 30 min). Preinjection of β₂-adrenergic receptor (AR) antagonist (ICI 118551) inhibited the increase in PGC-1α-b and PGC-1α-c mRNAs, but not the increase in PGC-1α-a mRNA, in response to high-intensity exercise. Although high-intensity exercise activated α2-AMP-activated protein kinase (α2-AMPK) in skeletal muscles, inactivation of α2-AMPK activity did not affect high-intensity exercise-induced mRNA expression of all PGC-1α isoforms, suggesting that activation of α2-AMPK is not mandatory for an increase in PGC-1α mRNA by high-intensity exercise. A single injection in mice of AICAR, an AMPK activator, increased mRNAs of all PGC-1α isoforms. AICAR increased blood catecholamine concentrations, and preinjection of β₂-AR antagonist inhibited the increase in PGC-1α-b and PGC-1α-c mRNAs but not the increase in PGC-1α-a mRNA. Direct exposure of epitrochlearis muscle to AICAR increased PGC-1α-a but not the -b isoform. These data indicate that exercise-induced PGC-1α expression was dependent on the intensity of exercise. Exercise or AICAR injection increased PGC-1α-b and PGC-1α-c mRNAs via β₂-AR activation, whereas high-intensity exercise increased PGC-1α-a expression by a multiple mechanism in which α2-AMPK is one of the signaling pathways.

‘Silent’ priming of translation-dependent LTP by β-adrenergic receptors involves phosphorylation and recruitment of AMPA receptors

The capacity for long-term changes in synaptic efficacy can be altered by prior synaptic activity, a process known as "metaplasticity." Activation of receptors for modulatory neurotransmitters can trigger downstream signaling cascades that persist beyond initial receptor activation and may thus have metaplastic effects. Because activation of β-adrenergic receptors (β-ARs) strongly enhances the induction of long-term potentiation (LTP) in the hippocampal CA1 region, we examined whether activation of these receptors also had metaplastic effects on LTP induction. Our results show that activation of β-ARs induces a protein synthesis-dependent form of metaplasticity that primes the future induction of late-phase LTP by a subthreshold stimulus. β-AR activation also induced a long-lasting increase in phosphorylation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) GluA1 subunits at a protein kinase A (PKA) site (S845) and transiently activated extracellular signal-regulated kinase (ERK). Consistent with this, inhibitors of PKA and ERK blocked the metaplastic effects of β-AR activation. β-AR activation also induced a prolonged, translation-dependent increase in cell surface levels of GluA1 subunit-containing AMPA receptors. Our results indicate that β-ARs can modulate hippocampal synaptic plasticity by priming synapses for the future induction of late-phase LTP through up-regulation of translational processes, one consequence of which is the trafficking of AMPARs to the cell surface.