Β1-adrenergic Receptor Activation Research Articles

Deconstructing cold-induced brown adipocyte neogenesis in mice.

Cold exposure triggers neogenesis in classic interscapular brown adipose tissue (iBAT) that involves activation of β1-adrenergic receptors, proliferation of PDGFRA+ adipose tissue stromal cells (ASCs), and recruitment of immune cells whose phenotypes are presently unknown. Single-cell RNA-sequencing (scRNA-seq) in mice identified three ASC subpopulations that occupied distinct tissue locations. Of these, interstitial ASC1 were found to be direct precursors of new brown adipocytes (BAs). Surprisingly, knockout of β1-adrenergic receptors in ASCs did not prevent cold-induced neogenesis, whereas pharmacological activation of the β3-adrenergic receptor on BAs was sufficient, suggesting that signals derived from mature BAs indirectly trigger ASC proliferation and differentiation. In this regard, cold exposure induced the delayed appearance of multiple macrophage and dendritic cell populations whose recruitment strongly correlated with the onset and magnitude of neogenesis across diverse experimental conditions. High-resolution immunofluorescence and single-molecule fluorescence in situ hybridization demonstrated that cold-induced neogenesis involves dynamic interactions between ASC1 and recruited immune cells that occur on the micrometer scale in distinct tissue regions. Our results indicate that neogenesis is not a reflexive response of progenitors to β-adrenergic signaling, but rather is a complex adaptive response to elevated metabolic demand within brown adipocytes.

Stachytine Hydrochloride Improves Cardiac Function in Mice with ISO-Induced Heart Failure by Inhibiting the α-1,6-Fucosylation on N-Glycosylation of β1AR.

Background: Cardiovascular diseases have become a major public health problem that seriously threatens human health. The cumulative effects of various cardiovascular events will eventually develop into chronic heart insufficiency and even heart failure, and the β1 adrenergic receptor signal pathway plays an important role in this process. Stachytine hydrochloride is the main active ingredient of Yimucao, which is a traditional Chinese medicine used to treat gynecological diseases. Modern studies have found that stachytine hydrochloride has a good cardioprotective effect, but it is still unclear whether stachytine hydrochloride has an effect on the β1 adrenergic receptor signal pathway. The purpose of this study is to explore the effect of stachytine hydrochloride on the β1 adrenergic receptor signal pathway. Method: In this study, a continuous infusion of isoproterenol (40 mg/kg/day) was administered to mice and ventricular myocytes explored the potential mechanism of stachytine hydrochloride (12 mg/kg/day) on the β1 adrenergic receptor signal pathway in the heart. Evaluate changes in cardiac morphology and function by echocardiography, cardiac hemodynamics, and histological methods, and detect molecular changes by Western blot and immunofluorescence. Treat primary cultured adult mouse or neonatal rat ventricular myocytes with or without isoproterenol (0.1 μMol), PNGase F (10–2 units/ml), and stachytine hydrochloride (10 μMol) at different time points. Detect α-1,6-fucosylation on N-glycosylation, calcium transient, contraction, and relaxation function and related signals. Results: Stachytine hydrochloride reduces cardiac remodeling and modulates hemodynamic parameters during chronic β1 adrenergic receptor activation in vivo. The N-glycosylation of β1 adrenergic receptors decreased after continuous isoproterenol stimulation, while stachytine hydrochloride can increase the N-glycosylation of β1AR in the heart of mice with isoproterenol-induced heart failure. Decreased N-glycosylation of β1 adrenergic receptors will downregulate the cAMP/PKA signal pathway and inhibit myocardial excitation and contraction coupling. Stachytine hydrochloride significantly reduced isoproterenol-induced cardiac N-linked glycoproteins with α-1,6-fucosylation. Conclusion: Our results show that stachytine hydrochloride inhibits the synthesis of α-1,6-fucosylation on the N-terminal sugar chain by reducing α-1,6-fucosyltransferase (FUT8) and α-1,3-mannosyl-glycoprotein 4-β-N-acetylglucosaminyltransferase A (MGAT4a), upregulating the N-glycosylation level on β1 adrenergic receptors, and maintaining cAMP/PKA signal pathway activation.

In This Issue

In This Issue

Three Generations of β-blockers: History, Class Differences and Clinical Applicability.

Beta-adrenergic receptors are expressed in cardiomyocytes and activated by either noradrenaline released from sympathetic synapses or circulating catecholamines. Their corresponding receptors have three subtypes, namely, β1, β2 and β3, which are members of the G protein-coupled receptors (GPCRs) family. Activation of β1-adrenergic receptors causes various physiological reactions including cardiac contraction and renin secretion from juxtaglomerular cells of the kidney. Antagonists of β-adrenergic receptors, known as β-blockers, have been used effectively for over four decades and have beneficial effects in the treatment of cardiovascular diseases. There are three generations of β-blockers according to their pharmacological properties. Firstgeneration β-blockers are non-selective, blocking both β1- and β2-receptors; second-generation β- blockers are more cardioselective in that they are more selective for β1-receptors; and thirdgeneration β-blockers are highly selective drugs for β1-receptors. The latter also display vasodilator actions by blocking α1-adrenoreceptors and activating β3-adrenergic receptors. In addition, thirdgeneration β-blockers exhibit angiogenic, antioxidant, anti-proliferative, anti-hypertrophic and antiapoptotic activities among other effects that are still under investigation. The objective of this review is to describe the evolution observed during the development of the three distinctive generations, thereby highlighting the advantages of third-generation β- blockers over the other two drug classes.

Noradrenaline Modulates the Membrane Potential and Holding Current of Medial Prefrontal Cortex Pyramidal Neurons via β1-Adrenergic Receptors and HCN Channels.

The medial prefrontal cortex (mPFC) receives dense noradrenergic projections from the locus coeruleus. Adrenergic innervation of mPFC pyramidal neurons plays an essential role in both physiology (control of memory formation, attention, working memory, and cognitive behavior) and pathophysiology (attention deficit hyperactivity disorder, posttraumatic stress disorder, cognitive deterioration after traumatic brain injury, behavioral changes related to addiction, Alzheimer’s disease and depression). The aim of this study was to elucidate the mechanism responsible for adrenergic receptor-mediated control of the resting membrane potential in layer V mPFC pyramidal neurons. The membrane potential or holding current of synaptically isolated layer V mPFC pyramidal neurons was recorded in perforated-patch and classical whole-cell configurations in slices from young rats. Application of noradrenaline (NA), a neurotransmitter with affinity for all types of adrenergic receptors, evoked depolarization or inward current in the tested neurons irrespective of whether the recordings were performed in the perforated-patch or classical whole-cell configuration. The effect of noradrenaline depended on β1- and not α1- or α2-adrenergic receptor stimulation. Activation of β1-adrenergic receptors led to an increase in inward Na+ current through hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which carry a mixed Na+/K+ current. The protein kinase A- and C-, glycogen synthase kinase-3β- and tyrosine kinase-linked signaling pathways were not involved in the signal transduction between β1-adrenergic receptors and HCN channels. The transduction system operated in a membrane-delimited fashion and involved the βγ subunit of G-protein. Thus, noradrenaline controls the resting membrane potential and holding current in mPFC pyramidal neurons through β1-adrenergic receptors, which in turn activate HCN channels via a signaling pathway involving the βγ subunit.

Abstract 464: Two Different Microdomains of β 1 -adrenoreceptor Signaling Revealed by Live Cell Imaging

Background: 3’,5’-cyclic adenosine monophosphate (cAMP) is an ubiquitous second messenger and a crucial regulator of cardiac function and disease. In cardiomyocytes, it is produced predominantly after activation of β 1 -adrenergic receptors (β 1 -ARs) by catecholamines and acts intracellularly in discrete functionally relevant microdomains formed, for example, around calcium-handling proteins. Previously, we reported that β 1 -ARs are distributed across various cardiomyocyte membrane areas, including transverse (T)-tubules and cell crests. However, it is unknown whether these two β 1 -AR pools contribute differentially to the regulation of cardiac contractility and gene expression. Methods and Results: To directly visualize receptor-microdomain communication in cardiomyocytes, we established a combination of scanning ion conductance microscopy (SICM) with transgenically expressed targeted Förster resonance energy transfer (FRET)-based biosensors. Using this approach, we measured local cAMP responses in distinct microdomains of mouse ventricular cardiomyocytes (such as plasma membrane, cytosol and nucleus) after localized stimulation of β 1 -AR on different membrane structures of healthy and diseased cardiomyocytes. Using a plasma membrane targeted cAMP biosensor, we found that β 1 -AR stimulation at the crest induced stronger cAMP signals compared to β 1 -AR stimulated in the T-tubuli where cAMP was highly confined by PDE3. This difference was abolished in a pressure overload hypertrophy model due to submembrane redistribution of PDEs. Interestingly, crest β 1 -AR signals could propagate deeper inside the cell, inducing higher nuclear cAMP responses than recorded from receptors stimulated in the T-tubules. Conclusions: in the present study, we have demonstrated that β 1 -ARs located in T-tubuli and cell crests form two differentially regulated cAMP microdomains, each having its typical PDE repertoire and generating distinct second messenger signals. More detailed understanding of these two microdomains at different subsarcolemmal locations may contribute to new therapeutic strategies including more specific β-blockers.

Phosphorylation of cardiac myosin binding protein C releases myosin heads from the surface of cardiac thick filaments

Cardiac myosin binding protein C (cMyBP-C) has a key regulatory role in cardiac contraction, but the mechanism by which changes in phosphorylation of cMyBP-C accelerate cross-bridge kinetics remains unknown. In this study, we isolated thick filaments from the hearts of mice in which the three serine residues (Ser273, Ser282, and Ser302) that are phosphorylated by protein kinase A in the m-domain of cMyBP-C were replaced by either alanine or aspartic acid, mimicking the fully nonphosphorylated and the fully phosphorylated state of cMyBP-C, respectively. We found that thick filaments from the cMyBP-C phospho-deficient hearts had highly ordered cross-bridge arrays, whereas the filaments from the cMyBP-C phospho-mimetic hearts showed a strong tendency toward disorder. Our results support the hypothesis that dephosphorylation of cMyBP-C promotes or stabilizes the relaxed/superrelaxed quasi-helical ordering of the myosin heads on the filament surface, whereas phosphorylation weakens this stabilization and binding of the heads to the backbone. Such structural changes would modulate the probability of myosin binding to actin and could help explain the acceleration of cross-bridge interactions with actin when cMyBP-C is phosphorylated because of, for example, activation of β1-adrenergic receptors in myocardium.

β1-Adrenergic receptor deficiency in ghrelin-expressing cells causes hypoglycemia in susceptible individuals.

Ghrelin is an orexigenic gastric peptide hormone secreted when caloric intake is limited. Ghrelin also regulates blood glucose, as emphasized by the hypoglycemia that is induced by caloric restriction in mouse models of deficient ghrelin signaling. Here, we hypothesized that activation of β1-adrenergic receptors (β1ARs) localized to ghrelin cells is required for caloric restriction-associated ghrelin release and the ensuing protective glucoregulatory response. In mice lacking the β1AR specifically in ghrelin-expressing cells, ghrelin secretion was markedly blunted, resulting in profound hypoglycemia and prevalent mortality upon severe caloric restriction. Replacement of ghrelin blocked the effects of caloric restriction in β1AR-deficient mice. We also determined that treating calorically restricted juvenile WT mice with beta blockers led to reduced plasma ghrelin and hypoglycemia, the latter of which is similar to the life-threatening, fasting-induced hypoglycemia observed in infants treated with beta blockers. These findings highlight the critical functions of ghrelin in preventing hypoglycemia and promoting survival during severe caloric restriction and the requirement for ghrelin cell-expressed β1ARs in these processes. Moreover, these results indicate a potential role for ghrelin in mediating beta blocker-associated hypoglycemia in susceptible individuals, such as young children.

Synthetic catecholamine triggers β1-adrenergic receptor activation and stimulates cardiotoxicity via oxidative stress mediated apoptotic cell death in rats: Abrogating action of thymol

Nowadays, there are considerable interests in the studies which are more connected with the impact of natural antioxidants against the free radical mediated damage in biological systems. Cardiotoxicity is one of the lethal manifestations of cardiovascular diseases (CVDs) which have been associated with the incidence of apoptotic cell death due to oxidative stress. We evaluated the impact of thymol, a dietary monoterpene phenol on isoproterenol (ISO), a synthetic catecholamine and a β1-adrenergic receptor agonist in rats. Thymol (7.5 mg/kg body weight) was pre and co-treated into male albino Wistar rats daily for a period of 7 days. Induction of cardiotoxicity was done by the subcutaneous administration of ISO (100 mg/kg body weight) into rats on 6th and 7th day. Cardiotoxicity in rats was confirmed by the increased levels/activity of serum troponin-T and creatine kinase in the serum alongwith decreased activity of creatine kinase in the heart. ISO induced cardiotoxic rats also showed a significant increase in the concentrations of lipid peroxidation products and a significant decrease in the activities/levels of antioxidants in the myocardium whereas Reverse Transcription Polymerase Chain Reaction study revealed an increased expression of caspase-8, caspase-9 and Fas genes along with a decreased expression of Bcl-xL gene in the myocardium. Thymol pre and co-treated ISO induced cardiotoxic rats showed considerable protective effects on all the biochemical parameters studied. Histopathological and in vitro findings are found in line with our biochemical findings. Thus, the present study revealed that thymol counters ISO induced cardiotoxicity by inhibiting oxidative stress and apoptotic cell death in rats by virtue of its potent antioxidant property.

An aerator for brain slice experiments in individual cell culture plate wells.

Ex vivo acute living brain slices are a broadly employed and powerful experimental preparation. Most new technology regarding this tissue has involved the chamber used when performing electrophysiological experiments. Alternatively we instead focus on the creation of a simple, versatile aerator designed to allow maintenance and manipulation of acute brain slices and potentially other tissue in a multi-well cell culture plate. Here we present an easily manufactured aerator designed to fit into a 24-well cell culture plate. It features a nylon mesh and a single microhole to enable gas delivery without compromising tissue stability. The aerator is designed to be individually controlled, allowing both high throughput and single well experiments. The aerator was validated by testing material leach, dissolved oxygen delivery, brain slice viability and neuronal electrophysiology. Example experiments are also presented, including a test of whether β1-adrenergic receptor activation regulates gene expression in ex vivo dorsal striatum using qPCR. Key differences include enhanced control over gas delivery to individual wells containing brain slices, decreased necessary volume, a sample restraint to reduce movement artifacts, the potential to be sterilized, the avoidance of materials that absorb water and small biological molecules, minimal production costs, and increased experimental throughput. This new aerator is of high utility and will be useful for experiments involving brain slices and other potentially tissue samples in 24-well cell culture plates.

β1-adrenergic receptor activation enhances memory in Alzheimer's disease model.

ObjectiveDeficits in social recognition and learning of social cues are major symptoms of neurodegenerative disorders such as Alzheimer's disease (AD). Here, we studied the role of β1-noradrenergic signaling in cognitive function to determine whether it could be used as a potential therapeutic target for AD.MethodsUsing pharmacological, biochemical, and behavioral tools, we assessed social recognition and the β1-adrenergic receptor (ADR) and its downstream protein kinase A (PKA)/phospho-cAMP response element-binding protein (pCREB) signaling cascade in the medial amygdala (MeA) in Thy1-hAPPLond/Swe+(APP) mouse model of AD.ResultsOur results demonstrated that APP mice display a significant social recognition deficit which is dependent on the β1-adrenergic system. Moreover, betaxolol, a selective β1-ADR antagonist, impaired social but not object/odor learning in C57Bl/6 mice. Our results identifies activation of the PKA/pCREB downstream of β1-ADR in MeA as responsible signaling cascade for learning of social cues in MeA. Finally, we found that xamoterol, a selective β1-ADR partial agonist, rescued the social recognition deficit of APP mice by increasing nuclear pCREB.InterpretationOur data indicate that activation of β1-ADR in MeA is essential for learning of social cues, and that an impairment of this cascade in AD may contribute to pathogenesis and cognitive deficits. Therefore, selective activation of β1-ADR may be used as a therapeutic approach to rescue memory deficits in AD. Further safety and translational studies will be needed to ensure the safety of this approach.

Circulation Editors’ Picks

<i>Circulation</i> Editors’ Picks

A Compartmentalized Model of the Beta1-Adrenergic Signaling System in Mouse Ventricular Myocytes

The β1-adrenergic signaling system plays an important role in heart function. Activation of this system increases heart rhythm, heart contraction. It also increases blood flow throughout the body. However, in disease, stimulation of β1-adrenergic receptors can increase an occurrence of arrhythmias. Therefore, comprehensive experimental study and modeling of the β1-adrenergic signaling system in the heart is of significant importance. We developed an experimentally-based mathematical model of β1-adrenergic regulation of the action potential and Ca2+ dynamics in mouse ventricular myocytes. The model includes several modules that describe biochemical reactions, electrical activity, and protein phosphorylation during activation of β1-adrenergic receptors. The model cell consists of three major compartments: caveolae, extracaveolae, and cytosol. Concentrations of β1-adrenergic receptors, as well as other signaling molecules, vary across the different domains. In the model, β1-adrenergic receptors are stimulated by the catecholamine isoproterenol. This leads to the activation of the Gs-protein signaling pathway, which ultimately increases cyclic AMP concentration and activity of protein kinase A to different degrees in different domains. The catalytic subunit of protein kinase A phosphorylates ion channels and Ca2+ handling proteins, leading to an increase or decrease in their function. Dephosphorylation is performed by the protein phosphatases 1 and 2A. Our model reproduces time-dependent behavior of a number of biochemical reactions and voltage-clamp data on ionic currents in mouse ventricular myocytes. The model also predicts action potential prolongation as well as an increase in intracellular Ca2+ transients dependent upon stimulation of β1-adrenergic receptors. The accuracy of the model was tested against experimental findings.

β1-Adrenergic receptors increase UCP1 in human MADS brown adipocytes and rescue cold-acclimated β3-adrenergic receptor-knockout mice via nonshivering thermogenesis

With the finding that brown adipose tissue is present and negatively correlated to obesity in adult man, finding the mechanism(s) of how to activate brown adipose tissue in humans could be important in combating obesity, type 2 diabetes, and their complications. In mice, the main regulator of nonshivering thermogenesis in brown adipose tissue is norepinephrine acting predominantly via β(3)-adrenergic receptors. However, vast majorities of β(3)-adrenergic agonists have so far not been able to stimulate human β(3)-adrenergic receptors or brown adipose tissue activity, and it was postulated that human brown adipose tissue could be regulated instead by β(1)-adrenergic receptors. Therefore, we have investigated the signaling pathways, specifically pathways to nonshivering thermogenesis, in mice lacking β(3)-adrenergic receptors. Wild-type and β(3)-knockout mice were either exposed to acute cold (up to 12 h) or acclimated for 7 wk to cold, and parameters related to metabolism and brown adipose tissue function were investigated. β(3)-knockout mice were able to survive both acute and prolonged cold exposure due to activation of β(1)-adrenergic receptors. Thus, in the absence of β(3)-adrenergic receptors, β(1)-adrenergic receptors are effectively able to signal via cAMP to elicit cAMP-mediated responses and to recruit and activate brown adipose tissue. In addition, we found that in human multipotent adipose-derived stem cells differentiated into functional brown adipocytes, activation of either β(1)-adrenergic receptors or β(3)-adrenergic receptors was able to increase UCP1 mRNA and protein levels. Thus, in humans, β(1)-adrenergic receptors could play an important role in regulating nonshivering thermogenesis.

β-Adrenergic Receptors Enhance Excitatory Transmission in the Bed Nucleus of the Stria Terminalis Through a Corticotrophin-Releasing Factor Receptor–Dependent and Cocaine-Regulated Mechanism

Evidence suggests that the noradrenergic and corticotrophin-releasing factor (CRF) systems play critical roles in relapse and stress-related behaviors. In particular, behavioral studies point to a serial signaling process initiated by β-adrenergic receptors that requires CRF receptor (CRFR)-dependent signaling in the bed nucleus of the stria terminalis (BNST) to produce stress-induced relapse to cocaine seeking. We used whole cell patch clamp recordings from acutely prepared mouse brain slices to examine the actions of β-adrenergic receptors and CRFR1 on excitatory transmission in BNST. We examined the effects of agonists of these receptors in slices prepared from naive, sham, and cocaine-conditioned mice. β(1)-adrenergic receptor activation within the BNST produces an enhancement of excitatory synaptic transmission that requires CRFR1-dependent signaling. We show that chronic cocaine administration transiently disrupts β(1)-adrenergic- and CRFR1-dependent enhancement of glutamatergic transmission, that this disruption wanes with time, and that it can be reintroduced with a cocaine challenge. In total, these studies identify a circuit mechanism within the BNST that may play an important role in CRF- and norepinephrine-regulated behaviors.

β1‐Adrenergic receptors activate two distinct signaling pathways in striatal neurons

Monoamine action in the dorsal striatum and nucleus accumbens plays essential roles in striatal physiology. Although research often focuses on dopamine and its receptors, norepinephrine (NE) and adrenergic receptors are also crucial in regulating striatal function. While noradrenergic neurotransmission has been identified in the striatum, little is known regarding the signaling pathways activated by β-adrenergic receptors in this brain region. Using cultured striatal neurons, we characterized a novel signaling pathway by which activation of β1-adrenergic receptors leads to the rapid phosphorylation of cAMP response element binding protein (CREB), a transcription-factor implicated as a molecular switch underlying long-term changes in brain function. NE-mediated CREB phosphorylation requires β1-adrenergic receptor stimulation of a receptor tyrosine kinase, ultimately leading to the activation of a Ras/Raf/MEK/MAPK/MSK signaling pathway. Activation of β1-adrenergic receptors also induces CRE-dependent transcription and increased c-fos expression. In addition, stimulation of β1-adrenergic receptors produces cAMP production, but surprisingly, β1-adrenergic receptor activation of adenylyl cyclase was not functionally linked to rapid CREB phosphorylation. These findings demonstrate that activation of β1-adrenergic receptors on striatal neurons can stimulate two distinct signaling pathways. These adrenergic actions can produce long-term changes in gene expression, as well as rapidly modulate cellular physiology. By elucidating the mechanisms by which NE and β1-adrenergic receptor activation affects striatal physiology, we provide the means to more fully understand the role of monoamines in modulating striatal function, specifically how NE and β1-adrenergic receptors may affect striatal physiology.

Nitric Oxide Can Mediate Beta-Adrenergic- and CaMKII-Dependent Spontaneous Ca2+ Waves in Cardiac Myocytes, Independent of PKA Activation

Increased diastolic SR Ca leak can initiate spontaneous Ca waves (SCaWs). SCaWs activate inward Na/Ca exchanger current causing an arrhythmogenic delayed afterdepolarization. Here we examine SCaWs in ventricular myocytes isolated from rabbit hearts. Myocytes did not exhibit SCaWs at baseline conditions, but 43% did when exposed to isoproterenol (ISO). This ISO-induced increase in activity was reversed by inhibition of CaMKII by KN93, but not with PKA inhibition by H89. At similar [Ca]SRT (121 μM) myocytes treated with ISO plus KN93 had significantly fewer SCaWs versus those treated with ISO or ISO plus H89 (0.2±0.28 vs. 1.1±0.28 & 1.29±0.39 SCaWs cell−1, respectively). We attribute this increase in activity to the previously characterized CaMKII-dependent increase in RyR-dependent leak. We also find that SR Ca leak is increased by the nitric oxide (NO) donor, SNAP; and this NO-dependent effect is also completely reversed by KN-93. We also show the increase in leak to be dependent on nitric oxide synthase 1 (NOS1) activity. At comparable SR Ca load (132 μM) ISO treated myocytes have significantly higher leak vs. control (8.4 vs. 3.8 μM). The ISO-induced leak (at constant SR Ca load) was attenuated by the NOS1 inhibitor, SMLT, but not the NOS3 inhibitor, L-NIO (3.5 vs. 6.8 μM). Moreover, ISO causes an upward trend in myocyte [NO] (sensed by the NO-dependent dye, DAF-2 A), and the NOS inhibitor, L-NAME significantly attenuated the development of SCaWs. Together this data suggests a novel pathway in which β1-adrenergic receptor activation stimulates NO production via NOS1, which in turn activates CaMKII to increase RyR gating, SR Ca leak, SCaWs and delayed afterdepolarizations.

Real-time optical recording of β1-adrenergic receptor activation reveals supersensitivity of the Arg389 variant to carvedilol

Antagonists of beta-adrenergic receptors (beta-ARs) have become a main therapeutic regimen for the treatment of heart failure even though the mechanisms of their beneficial effects are still poorly understood. Here, we used fluorescent resonance energy transfer-based (FRET-based) approaches to directly monitor activation of the beta(1)-AR and downstream signaling. While the commonly used beta-AR antagonists metoprolol, bisoprolol, and carvedilol displayed varying degrees of inverse agonism on the Gly389 variant of the receptor (i.e., actively switching off the beta(1)-AR), surprisingly, only carvedilol showed very specific and marked inverse agonist effects on the more frequent Arg389 variant. These specific effects of carvedilol on the Arg389 variant of the beta(1)-AR were also seen for control of beating frequency in rat cardiac myocytes expressing the 2 receptor variants. This FRET sensor permitted direct observation of activation of the beta(1)-AR in living cells in real time. It revealed that beta(1)-AR variants dramatically differ in their responses to diverse beta blockers, with possible consequences for their clinical use.

Antiadrenergic therapy of chronic heart failure: surprises and new opportunities.

The great British-American scientist-philosopher Alfred North Whitehead divided progress into three stages, the second of which was termed precision, in which the “right ways and wrong ways” of an original idea are elucidated.1 During this period, reinterpretation of the basic idea occurs and is essential to progress. Whitehead’s message is that important ideas are dynamic instruments that are constantly changing as new and usually unexpected information becomes available. This is why tests of particular hypotheses, including those tested in Phase III clinical trials, are often unsupportive, and why therapeutic paradigms constantly change. Within such an ephemeral milieu, the key to ultimate success is to view each unexpected or negative result as an opportunity for constructing and testing even more novel and valuable hypotheses within the framework of the general idea, to ascend to the final stage where progress can be “generalized.”1 Whitehead’s philosophical legacy is impressively in play in the area of antiadrenergic therapy of chronic heart failure (CHF). The unarguable basic idea is that the biologically powerful adrenergic compensatory mechanism plays a critical role in the natural history of CHF. It is the details or nuances within the general paradigm that continue to change, and lately, surprisingly so. As recently reviewed,2 the importance of dysfunctional adrenergic activation in CHF was first elucidated by work performed by Braunwald’s group at the National Institutes of Health in the 1960s. Among other things, this early work provided the first evidence of marked adrenergic activation in CHF. However, on the basis of reduction in myocardial tissue norepinephrine, and the short-term effects of large doses of antiadrenergic agents,3 the overall interpretation was that adrenergic support was deficient in CHF. This view prevailed for 10 to 15 years, and it contributed to the original logic behind developing Type III phosphodiesterase inhibitors …

Targeted disruption of the Nhe1 gene fails to inhibit beta(1)-adrenergic receptor-induced parotid gland hypertrophy.

Chronic beta(1)-adrenergic receptor activation results in hypertrophy and hyperplasia of rodent salivary gland acinar cells. Na(+)/H(+) exchanger isoform 1 (NHE1) regulates cell volume and the induction of cell proliferation in many tissues. To investigate the relationship between NHE1 and the response of parotid glands to beta(1)-adrenergic agonists, we examined by Northern blot analysis NHE1 expression in saline-treated mice and mice 30 min and 2, 6, and 24 h after isoproterenol injection. NHE1 transcripts increased approximately 50% by 2 h, and a more than twofold increase was noted at 24 h. Isoproterenol did not acutely increase Na(+)/H(+) exchanger activity; however, exchanger activity was significantly elevated by 24 h. To test whether NHE1 activity is essential for inducing salivary gland hypertrophy in vivo, mice with targeted disruption of Nhe1 were treated with isoproterenol. Na(+)/H(+) exchanger activity was absent in acinar cells from Nhe1(-/-) mice, nevertheless, the lack of NHE1 failed to inhibit isoproterenol-induced hypertrophy. These data directly demonstrate that acinar cell hypertrophy induced by chronic beta(1)-adrenergic receptor stimulation occurs independently of NHE1 activity.