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A Systematic Review of Inverse Agonism at Adrenoceptor Subtypes. Cells 2020; 9:cells9091923. [PMID: 32825009 PMCID: PMC7564766 DOI: 10.3390/cells9091923] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 08/16/2020] [Accepted: 08/18/2020] [Indexed: 12/18/2022] Open
Abstract
As many, if not most, ligands at G protein-coupled receptor antagonists are inverse agonists, we systematically reviewed inverse agonism at the nine adrenoceptor subtypes. Except for β3-adrenoceptors, inverse agonism has been reported for each of the adrenoceptor subtypes, most often for β2-adrenoceptors, including endogenously expressed receptors in human tissues. As with other receptors, the detection and degree of inverse agonism depend on the cells and tissues under investigation, i.e., they are greatest when the model has a high intrinsic tone/constitutive activity for the response being studied. Accordingly, they may differ between parts of a tissue, for instance, atria vs. ventricles of the heart, and within a cell type, between cellular responses. The basal tone of endogenously expressed receptors is often low, leading to less consistent detection and a lesser extent of observed inverse agonism. Extent inverse agonism depends on specific molecular properties of a compound, but inverse agonism appears to be more common in certain chemical classes. While inverse agonism is a fascinating facet in attempts to mechanistically understand observed drug effects, we are skeptical whether an a priori definition of the extent of inverse agonism in the target product profile of a developmental candidate is a meaningful option in drug discovery and development.
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Rozier K, Bondarenko VE. Distinct physiological effects of β1- and β2-adrenoceptors in mouse ventricular myocytes: insights from a compartmentalized mathematical model. Am J Physiol Cell Physiol 2017; 312:C595-C623. [DOI: 10.1152/ajpcell.00273.2016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Revised: 01/03/2017] [Accepted: 01/18/2017] [Indexed: 01/08/2023]
Abstract
The β1- and β2-adrenergic signaling systems play different roles in the functioning of cardiac cells. Experimental data show that the activation of the β1-adrenergic signaling system produces significant inotropic, lusitropic, and chronotropic effects in the heart, whereas the effects of the β2-adrenergic signaling system is less apparent. In this paper, a comprehensive compartmentalized experimentally based mathematical model of the combined β1- and β2-adrenergic signaling systems in mouse ventricular myocytes is developed to simulate the experimental findings and make testable predictions of the behavior of the cardiac cells under different physiological conditions. Simulations describe the dynamics of major signaling molecules in different subcellular compartments; kinetics and magnitudes of phosphorylation of ion channels, transporters, and Ca2+ handling proteins; modifications of action potential shape and duration; and [Ca2+]i and [Na+]i dynamics upon stimulation of β1- and β2-adrenergic receptors (β1- and β2-ARs). The model reveals physiological conditions when β2-ARs do not produce significant physiological effects and when their effects can be measured experimentally. Simulations demonstrated that stimulation of β2-ARs with isoproterenol caused a marked increase in the magnitude of the L-type Ca2+ current, [Ca2+]i transient, and phosphorylation of phospholamban only upon additional application of pertussis toxin or inhibition of phosphodiesterases of type 3 and 4. The model also made testable predictions of the changes in magnitudes of [Ca2+]i and [Na+]i fluxes, the rate of decay of [Na+]i concentration upon both combined and separate stimulation of β1- and β2-ARs, and the contribution of phosphorylation of PKA targets to the changes in the action potential and [Ca2+]i transient.
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Affiliation(s)
- Kelvin Rozier
- Department of Mathematics and Statistics, Georgia State University, Atlanta, Georgia; and
| | - Vladimir E. Bondarenko
- Department of Mathematics and Statistics, Georgia State University, Atlanta, Georgia; and
- Neuroscience Institute, Georgia State University, Atlanta, Georgia
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Grajales L, Lach LE, Janisch P, Geenen DL, García J. Temporal expression of calcium channel subunits in satellite cells and bone marrow mesenchymal cells. Stem Cell Rev Rep 2016; 11:408-22. [PMID: 25277766 DOI: 10.1007/s12015-014-9566-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Bone marrow-derived mesenchymal stem cells (MSC) can be differentiated into myocytes, as well as adipocytes, chondrocytes, and osteocytes in culture. Calcium channels mediate excitation-contraction coupling and are essential for the function of muscle. However, little is known about the expression of calcium channel subunits and calcium handling in stem cells. We examined whether the expression of calcium channel subunits in MSC is similar to that of skeletal muscle satellite cells and if their levels of expression are modified after treatment with bone morphogenetic protein-4 (BMP4). We found that during myogenic differentiation, MSC first express the α2δ1 subunit and the cardiac channel subunit Cav1.2. In contrast to the α2δ1 subunit levels, the Cav1.2 subunit decreases rapidly with time. The skeletal channel subunit Cav1.1 is detected at day 3 but its expression increases considerably, resembling more closely the expression of the subunits in satellite cells. Treatment of MSC with BMP4 caused a significant increase in expression of Cav1.2, a delay in expression of Cav1.1, and a reduction in the duration of calcium transients when extracellular calcium was removed. Calcium currents and transients followed a pattern related to the expression of the cardiac (Cav1.2) or skeletal (Cav1.1) α1subunits. These results indicate that differentiation of untreated MSC resembles differentiation of skeletal muscle and that BMP4 reduces skeletal muscle calcium channel expression and promotes the expression of cardiac calcium channels during myogenic differentiation.
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Affiliation(s)
- Liliana Grajales
- Department of Physiology and Biophysics, University of Illinois at Chicago, 835 South Wolcott Ave, Chicago, IL, 60612, USA
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Kashihara T, Hirose M, Shimojo H, Nakada T, Gomi S, Hongo M, Yamada M. β(2)-Adrenergic and M(2)-muscarinic receptors decrease basal t-tubular L-type Ca2+ channel activity and suppress ventricular contractility in heart failure. Eur J Pharmacol 2013; 724:122-31. [PMID: 24389135 DOI: 10.1016/j.ejphar.2013.12.037] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Revised: 11/29/2013] [Accepted: 12/15/2013] [Indexed: 01/01/2023]
Abstract
L-type Ca(2+) channels (LTCC) play a crucial role in cardiac excitation-contraction coupling. We previously found that in failing ventricular myocytes of mice chronically treated with isoproterenol, basal t-tubular (TT) LTCC activity was halved by activation of protein phosphatase (PP)2A whereas basal surface sarcolemmal (SS) LTCC activity was doubled by inhibition of PP1. Interestingly, chronic treatment of these mice with pertussis toxin almost completely normalized TT and SS LTCC densities and cardiac contractility. In the present study, we therefore sought to identify the Gi/o protein-coupled receptors in cardiac myocytes (i.e. β2-adrenergic, M2-muscarinic and A1-adenosine receptors) that are responsible for these abnormalities in heart failure by chronically administrating mice a selective antagonist of each receptor (ICI118,551, atropine and 8-cyclopentyl-1,3-dipropilxanthine (DPCPX), respectively) with isoproterenol. Compared with mice treated with isoproterenol alone, mice treated with isoproterenol plus ICI118,551 or atropine, but not DPCPX showed significantly lower lung weight/tibial length, higher fractional shortening, lower left ventricular end-diastolic pressure and higher dP/dtmax and dP/dtmin. In addition, ventricular myocytes of mice treated with isoproterenol plus ICI118,551 or atropine, but not DPCPX exhibited significantly higher TT and lower SS LTCC current densities than those of mice treated with isoproterenol alone due to normalization of the PP activities. These results indicate that β2-adrenergic, M2-muscarinic, but not A1-adenosine receptors contribute to reduced ventricular contractility at least partially by decreasing basal TT LTCC activity in heart failure. Therefore, antagonists of β2-adrenergic and/or M2-muscarinic receptors can be good adjuncts to β1-adrenergic receptor antagonists in the treatment of heart failure.
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Affiliation(s)
- Toshihide Kashihara
- Department of Molecular Pharmacology, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan
| | - Masamichi Hirose
- Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Iwate Medical University, Morioka, Iwate, Japan
| | - Hisashi Shimojo
- Department of Pathology, Shinshu University School of Medicine, Matsumoto, Nagano, Japan
| | - Tsutomu Nakada
- Department of Molecular Pharmacology, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan
| | - Simmon Gomi
- Department of Molecular Pharmacology, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan; Department of Cardiovascular Medicine, Shinshu University School of Medicine, Matsumoto, Nagano, Japan
| | - Minoru Hongo
- Department of Cardiovascular Medicine, Shinshu University School of Health Science, Matsumoto, Nagano, Japan
| | - Mitsuhiko Yamada
- Department of Molecular Pharmacology, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan.
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Kenakin T. New concepts in pharmacological efficacy at 7TM receptors: IUPHAR review 2. Br J Pharmacol 2013; 168:554-75. [PMID: 22994528 PMCID: PMC3579279 DOI: 10.1111/j.1476-5381.2012.02223.x] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Revised: 08/03/2012] [Accepted: 09/12/2012] [Indexed: 01/14/2023] Open
Abstract
The present-day concept of drug efficacy has changed completely from its original description as the property of agonists that causes tissue activation. The ability to visualize the multiple behaviours of seven transmembrane receptors has shown that drugs can have many efficacies and also that the transduction of drug stimulus to various cellular stimulus-response cascades can be biased towards some but not all pathways. This latter effect leads to agonist 'functional selectivity', which can be favourable for the improvement of agonist therapeutics. However, in addition, biased agonist potency becomes cell type dependent with the loss of the monotonic behaviour of stimulus-response mechanisms, leading to potential problems in agonist quantification. This has an extremely important effect on the discovery process for new agonists since it now cannot be assumed that a given screening or lead optimization assay will correctly predict therapeutic behaviour. This review discusses these ideas and how new approaches to quantifying agonist effect may be used to circumvent the cell type dependence of agonism. This article, written by a corresponding member of the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR), reviews our current understanding of the interaction of ligands with seven transmembrane receptors. Further information on these pharmacological concepts is being incorporated into the IUPHAR/BPS database GuideToPharmacology.org.
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Affiliation(s)
- Terry Kenakin
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, NC, USA.
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Jiang X, Xu C, Wang Y, Gao L, Yan C, Li D, Sun H. β2-adrenoceptor transfection enhances contractile reserve of isolated rat ventricular myocytes exposed to chronic isoprenaline stimulation by improving β1-adrenoceptor responsiveness. J Recept Signal Transduct Res 2012; 32:36-41. [PMID: 22216755 DOI: 10.3109/10799893.2011.610107] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
CONTEXT Heart failure (HF) is a progressive deterioration in heart function associated with overactivity of the sympathetic nervous system. Elevated sympathetic nervous system activity down regulates the β-adrenergic signal system, suppressing β-adrenoceptors (β-ARs)-mediated contractile support in the failing heart. OBJECTIVE We investigated the effects of β(2)-AR gene transfer on shortening amplitude of isolated ventricular myocytes under chronic exposure to isoprenaline (ISO), and further determine the contributions of β(1)-AR and β(2)-AR to the contraction. MATERIALS AND METHODS Cardiomyocytes were isolated from adult rat hearts and then transfected with β(2)-AR gene using an adenovirus vector. Four hours after the infection, cardiomyocytes were treated with ISO for another 24 hours to imitate high levels of circulating catecholamines in HF. Western blotting was performed to measure myocardial protein expression of β(2)-AR. Video-based edge-detection system was used to evaluate basal and ISO-stimulated shortening amplitudes of cardiomyocytes. RESULTS β(2)-AR gene transfer increased β(2)-AR protein content. Chronic ISO stimulation produced a negative inotropic response, whereas acute ISO stimulation showed a positive inotropic response. β(2)-AR gene transfer had no significant effects on shortening amplitude of cardiomyocytes under normal conditions, but enhanced the blunted contraction of cardiomyocytes under pathological conditions induced by chronic ISO stimulation, and the effect was inhibited by β(1)-AR antagonist, CGP 20712A, instead of β(2)-AR antagonist, ICI 118,551. DISCUSSION AND CONCLUSIONS We conclude that β(2)-AR gene transfer in isolated ventricular myocytes under chronic ISO stimulation improves cellular contraction, and the beneficial effects might be mediated by improving β(1)-adrenoceptor responsiveness.
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Affiliation(s)
- XinWei Jiang
- Department of Physiology, Xuzhou Medical College, Xuzhou, China
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Jensen BC, O'Connell TD, Simpson PC. Alpha-1-adrenergic receptors: targets for agonist drugs to treat heart failure. J Mol Cell Cardiol 2010; 51:518-28. [PMID: 21118696 DOI: 10.1016/j.yjmcc.2010.11.014] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2010] [Accepted: 11/12/2010] [Indexed: 12/19/2022]
Abstract
Evidence from cell, animal, and human studies demonstrates that α1-adrenergic receptors mediate adaptive and protective effects in the heart. These effects may be particularly important in chronic heart failure, when catecholamine levels are elevated and β-adrenergic receptors are down-regulated and dysfunctional. This review summarizes these data and proposes that selectively activating α1-adrenergic receptors in the heart might represent a novel and effective way to treat heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."
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Affiliation(s)
- Brian C Jensen
- Cardiology Division, VA Medical Center, San Francisco, CA, USA.
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Xu L, Lai D, Cheng J, Lim HJ, Keskanokwong T, Backs J, Olson EN, Wang Y. Alterations of L-type calcium current and cardiac function in CaMKII{delta} knockout mice. Circ Res 2010; 107:398-407. [PMID: 20538682 DOI: 10.1161/circresaha.110.222562] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Recent studies have highlighted important roles of CaMKII in regulating Ca(2+) handling and excitation-contraction coupling. However, the cardiac effect of chronic CaMKII inhibition has not been well understood. OBJECTIVE We have tested the alterations of L-type calcium current (I(Ca)) and cardiac function in CaMKIIdelta knockout (KO) mouse left ventricle (LV). METHODS AND RESULTS We used the patch-clamp method to record I(Ca) in ventricular myocytes and found that in KO LV, basal I(Ca) was significantly increased without changing the transmural gradient of I(Ca) distribution. Substitution of Ba(2+) for Ca(2+) showed similar increase in I(Ba). There was no change in the voltage dependence of I(Ca) activation and inactivation. I(Ca) recovery from inactivation, however, was significantly slowed. In KO LV, the Ca(2+)-dependent I(Ca) facilitation (CDF) and I(Ca) response to isoproterenol (ISO) were significantly reduced. However, ISO response was reversed by beta2-adrenergic receptor (AR) inhibition. Western blots showed a decrease in beta1-AR and an increase in Ca(v)1.2, beta2-AR, and Galphai3 protein levels. Ca(2+) transient and sarcomere shortening in KO myocytes were unchanged at 1-Hz but reduced at 3-Hz stimulation. Echocardiography in conscious mice revealed an increased basal contractility in KO mice. However, cardiac reserve to work load and beta-adrenergic stimulation was reduced. Surprisingly, KO mice showed a reduced heart rate in response to work load or beta-adrenergic stimulation. CONCLUSIONS Our results implicate physiological CaMKII activity in maintaining normal I(Ca), Ca(2+) handling, excitation-contraction coupling, and the in vivo heart function in response to cardiac stress.
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Affiliation(s)
- Lin Xu
- Department of Pediatrics and Children's Healthcare of Atlanta, Emory University, GA, USA
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Kenakin T. Collateral efficacy in drug discovery: taking advantage of the good (allosteric) nature of 7TM receptors. Trends Pharmacol Sci 2007; 28:407-15. [PMID: 17629960 DOI: 10.1016/j.tips.2007.06.009] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2006] [Revised: 05/25/2007] [Accepted: 06/29/2007] [Indexed: 10/23/2022]
Abstract
Seven-transmembrane receptors are prototypic allosteric proteins with the ability to adopt numerous conformations, many of which interact with cellular partners to initiate cellular biochemical processes. Defining efficacy as the ability of ligands to stabilize some of these conformations (which, in turn, possess physiological activity) presents a wider definition of efficacy beyond simple integrated cellular response; numerous or 'pluridimensional' efficacies are required to describe ligands. Specifically, some agonists might only partially activate the library of potential signaling systems in a cell or some antagonists might actively induce receptor internalization without activation. This article reviews data to demonstrate that there is no longer support for a linear view of efficacy whereby a single receptor activation state triggers all possible receptor interactions with a cell. Instead, a view of collateral efficacy, in which ligands can produce portions of the possible behaviors of receptors, is presented. Concepts related to the molecular mechanism for this effect (discussed in the literature as 'stimulus trafficking', 'biased agonism' or 'functional selectivity') and discussion of the possible therapeutic implications of this mechanism are presented.
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Affiliation(s)
- Terry Kenakin
- Department of Biochemical Reagents and Assay Development, GlaxoSmithKline Research and Development, 5 Moore Drive, Research Triangle Park, NC 27709, USA.
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11
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Kenakin T. Collateral efficacy as a pharmacological problem applied to new drug discovery. Expert Opin Drug Discov 2006; 1:635-52. [DOI: 10.1517/17460441.1.7.635] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Grandy SA, Denovan-Wright EM, Ferrier GR, Howlett SE. Overexpression of human beta2-adrenergic receptors increases gain of excitation-contraction coupling in mouse ventricular myocytes. Am J Physiol Heart Circ Physiol 2004; 287:H1029-38. [PMID: 15155261 DOI: 10.1152/ajpheart.00814.2003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study investigated cardiac excitation-contraction coupling at 37 degrees C in transgenic mice with cardiac-specific overexpression of human beta2-adrenergic receptors (TG4 mice). In field-stimulated myocytes, contraction was significantly greater in TG4 compared with wild-type (WT) ventricular myocytes. In contrast, when duration of depolarization was controlled with rectangular voltage clamp steps, contraction amplitudes initiated by test steps were the same in WT and TG4 myocytes. When cells were voltage clamped with action potentials simulating TG4 and WT action potential configurations, contractions were greater with long TG4 action potentials and smaller with shorter WT action potentials, which suggests an important role for action potential configuration. Interestingly, peak amplitude of L-type Ca2+ current (I(Ca-L)) initiated by rectangular test steps was reduced, although the voltage dependencies of contractions and currents were not altered. To explore the basis for the altered relation between contraction and I(Ca-L), Ca2+ concentrations were measured in myocytes loaded with fura 2. Diastolic concentrations of free Ca2+ and amplitudes of Ca2+ transients were similar in voltage-clamped myocytes from WT and TG4 mice. However, sarcoplasmic reticulum (SR) Ca2+ content assessed with the rapid application of caffeine was elevated in TG4 cells. Increased SR Ca2+ was accompanied by increased frequency and amplitudes of spontaneous Ca2+ sparks measured at 37 degrees C with fluo 3. These observations suggest that the gain of Ca(2+)-induced Ca2+ release is increased in TG4 myocytes. Increased gain counteracts the effects of decreased amplitude of I(Ca-L) in voltage-clamped myocytes and likely contributes to increased contraction amplitudes in field-stimulated TG4 myocytes.
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Affiliation(s)
- Scott A Grandy
- Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7
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Chakir K, Xiang Y, Yang D, Zhang SJ, Cheng H, Kobilka BK, Xiao RP. The third intracellular loop and the carboxyl terminus of beta2-adrenergic receptor confer spontaneous activity of the receptor. Mol Pharmacol 2003; 64:1048-58. [PMID: 14573753 DOI: 10.1124/mol.64.5.1048] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
It is well established that the beta2-adrenergic receptor (beta2-AR) exhibits a robust ligand-independent activity, whereas this property is considerably weaker in the closely related beta1-AR subtype. To identify the potential domain(s) of beta2-AR responsible for the spontaneous receptor activation, we created three chimeras in which the third intracellular loop (beta1/beta2-Li3) or the carboxyl terminus (beta1/beta2-CT) or both domains (beta1/beta2-Li3CT) of beta1-AR are replaced by the corresponding parts of the beta2-AR. Using adenoviral gene transfer, we individually expressed these beta1/beta2-AR chimeras in mouse cardiomyocytes lacking both native beta1-AR and beta2-AR (beta1/beta2 double knockout), and examined their possible spontaneous activities. Overexpression of these beta1/beta2-AR chimeras markedly elevated basal cAMP accumulation and myocyte contractility in the absence of agonist stimulation compared with those infected by a control adenovirus expressing beta-galactosidase or an adenovirus expressing wild type beta1-AR. These effects were fully reversed by a beta2-AR inverse agonist, (+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol (ICI 118,551; 5 x 10-7 M), regardless of inhibition of Gi with pertussis toxin, but not by a panel of beta1-AR antagonists, including [2-(3-carbamoyl-4-hydroxyphenoxy)-ethylamino]-3-[4-(1-methyl-4-trifluormethyl-2-imidazolyl)-phenoxy]-2-propanolmethanesulfonate (CGP20712A), betaxolol, bisoprolol, and metoprolol. Furthermore, we have shown that the C-terminal postsynaptic density 95/disc-large/ZO-1 (PDZ) motif of beta1-AR is not responsible for the lack of beta1-AR spontaneous activation, although it has been known that the beta1-AR PDZ motif prevents the receptor from undergoing agonist-induced trafficking and Gi coupling in cardiomyocytes. Taken together, the present results indicate that both the third intracellular loop and the C terminus are involved in beta2-AR spontaneous activation and that either domain seems to be sufficient to confer the receptor spontaneous activity.
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MESH Headings
- Adrenergic beta-Antagonists/pharmacology
- Animals
- Cells, Cultured
- Cyclic AMP/metabolism
- Imidazoles/pharmacology
- Isoproterenol/pharmacology
- Mice
- Myocardial Contraction/drug effects
- Myocardium/metabolism
- Propanolamines/pharmacology
- Protein Conformation
- Protein Structure, Tertiary
- Receptors, Adrenergic, beta-1/genetics
- Receptors, Adrenergic, beta-1/metabolism
- Receptors, Adrenergic, beta-2/chemistry
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/metabolism
- Recombinant Fusion Proteins
- Signal Transduction/physiology
- Subcellular Fractions
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Affiliation(s)
- Khalid Chakir
- Laboratory of Cardiovascular Science, Gerontology Research Center, NIA, NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224, USA
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Xiao RP, Zhang SJ, Chakir K, Avdonin P, Zhu W, Bond RA, Balke CW, Lakatta EG, Cheng H. Enhanced G(i) signaling selectively negates beta2-adrenergic receptor (AR)--but not beta1-AR-mediated positive inotropic effect in myocytes from failing rat hearts. Circulation 2003; 108:1633-9. [PMID: 12975249 DOI: 10.1161/01.cir.0000087595.17277.73] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
BACKGROUND Myocardial contractile response to beta1- and beta2-adrenergic receptor (AR) stimulation is severely impaired in chronic heart failure, in which G(i) signaling and the ratio of beta2/beta1 are often increased. Because beta2-AR but not beta1-AR couples to G(s) and G(i) with the G(i) coupling negating the G(s)-mediated contractile response, we determined whether the heart failure-associated augmentation of G(i) signaling contributes differentially to the defects of these beta-AR subtypes and, if so, whether inhibition of G(i) or selective activation of beta2-AR/G(s) by ligands restores beta2-AR contractile response in the failing heart. METHODS AND RESULTS Cardiomyocytes were isolated from 18- to 24-month-old failing spontaneously hypertensive (SHR) or age-matched Wistar-Kyoto (WKY) rat hearts. In SHR cardiomyocytes, either beta-AR subtype-mediated inotropic effect was markedly diminished, whereas G(i) proteins and the beta2/beta1 ratio were increased. Disruption of G(i) signaling by pertussis toxin (PTX) enabled beta2- but not beta1-AR to induce a full positive inotropic response in SHR myocytes. Furthermore, screening of a panel of beta2-AR ligands revealed that the contractile response mediated by most beta2-AR agonists, including zinterol, salbutamol, and procaterol, was potentiated by PTX, indicating concurrent G(s) and G(i) activation. In contrast, fenoterol, another beta2-AR agonist, induced a full positive inotropic effect in SHR myocytes even in the absence of PTX. CONCLUSIONS We conclude that enhanced G(i) signaling is selectively involved in the dysfunction of beta2- but not beta1-AR in failing SHR hearts and that disruption of G(i) signaling by PTX or selective activation of beta2-AR/G(s) signaling by fenoterol restores the blunted beta2-AR contractile response in the failing heart.
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MESH Headings
- Adrenergic beta-1 Receptor Antagonists
- Adrenergic beta-2 Receptor Agonists
- Adrenergic beta-Agonists/pharmacology
- Animals
- Cardiac Output, Low/etiology
- Cardiac Output, Low/metabolism
- Cardiac Output, Low/physiopathology
- Cardiotonic Agents/pharmacology
- Cells, Cultured
- Chronic Disease
- Fenoterol/pharmacology
- GTP-Binding Protein alpha Subunits, Gi-Go/antagonists & inhibitors
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- Heterotrimeric GTP-Binding Proteins/analysis
- Ligands
- Myocardial Contraction/drug effects
- Myocardium/chemistry
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/physiology
- Pertussis Toxin/pharmacology
- Rats
- Rats, Inbred SHR
- Rats, Inbred WKY
- Receptors, Adrenergic, beta-1/analysis
- Receptors, Adrenergic, beta-1/metabolism
- Receptors, Adrenergic, beta-2/analysis
- Receptors, Adrenergic, beta-2/metabolism
- Signal Transduction/drug effects
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Affiliation(s)
- Rui-Ping Xiao
- the Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Md 21224, USA.
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Jurevicius J, Skeberdis VA, Fischmeister R. Role of cyclic nucleotide phosphodiesterase isoforms in cAMP compartmentation following beta2-adrenergic stimulation of ICa,L in frog ventricular myocytes. J Physiol 2003; 551:239-52. [PMID: 12815180 PMCID: PMC2343164 DOI: 10.1113/jphysiol.2003.045211] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2003] [Accepted: 06/02/2003] [Indexed: 02/02/2023] Open
Abstract
The role of cyclic nucleotide phosphodiesterase (PDE) isoforms in the beta2-adrenergic stimulation of the L-type Ca2+ current (ICa,L) was investigated in frog ventricular myocytes using double patch-clamp and double-barrelled microperfusion techniques. Isoprenaline (ISO, 1 nM to 10 microM) was applied on one half of the cell, either alone or in the presence of PDE inhibitors, and the local and distant responses of ICa,L were used to determine the gradient of local vs. distant cAMP concentration (alpha). IBMX (100 microM), a non-selective PDE inhibitor, reduced alpha from 40 to 4.4 indicating a 9-fold reduction in intracellular cAMP compartmentation when all PDE activity was blocked. While PDE1 and PDE2 inhibition had no effect, PDE3 inhibition by milrinone (3 microM) or PDE4 inhibition by Ro 20-1724 (3 microM) reduced alpha by 6- and 4-fold, respectively. A simultaneous application of milrinone and Ro 20-1724 produced a similar effect to IBMX, showing that PDE3 and PDE4 were the major PDEs accounting for cAMP compartmentation. Okadaic acid (3 microM), a non-selective phosphatase inhibitor, or H89 (1 microM), an inhibitor of cAMP-dependent protein kinase (PKA), had no effect on the distant response of ICa,L to ISO indicating that PDE activation by PKA played a minor role in cAMP compartmentation. Our results demonstrate that PDE activity determines the degree of cAMP compartmentation in frog ventricular cells upon beta2-adrenergic stimulation. PDE3 and PDE4 subtypes play a major role in this process, and contribute equally to ensure a functional coupling of beta2-adrenergic receptors with nearby Ca2+ channels via local elevations of cAMP.
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Affiliation(s)
- Jonas Jurevicius
- Laboratoire de Cardiologie Cellulaire et Moléculaire, INSERM U-446, Université Paris-Sud, Faculté de Pharmacie, F-92296 Châtenay-Malabry, France
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16
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Affiliation(s)
- Terry Kenakin
- Systems Research, GlaxoSmithKline Research and Development, 5 Moore Drive, Research Triangle Park, NC 27709, USA.
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17
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Kenakin T. Predicting therapeutic value in the lead optimization phase of drug discovery. Nat Rev Drug Discov 2003; 2:429-38. [PMID: 12776218 DOI: 10.1038/nrd1110] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Recombinant and natural cellular assays for human G-protein-coupled receptors are used to optimize initial lead molecules obtained from screening. Although the activity of these molecules can be assessed on human genotype receptors, there is increasing evidence that cells impose a phenotypic selectivity to molecules in various cellular backgrounds. This opens the possibility of dissimulations between activity seen in lead optimization assays and the intended therapeutic value in humans. This review discusses the mechanisms by which cells can impose phenotypic selectivity on molecules and approaches to reduce this practical problem for drug discovery.
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Affiliation(s)
- Terry Kenakin
- Systems Research, GlaxoSmithKline Research and Development, 5 Moore Drive, Research Triangle Park, North Carolina 27709, USA.
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18
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Opposite action of beta1- and beta2-adrenergic receptors on Ca(V)1 L-channel current in rat adrenal chromaffin cells. J Neurosci 2003. [PMID: 12514203 DOI: 10.1523/jneurosci.23-01-00073.2003] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Voltage-gated Ca(2+) channels of chromaffin cells are modulated by locally released neurotransmitters through autoreceptor-activated G-proteins. Clear evidence exists in favor of a Ca(2+) channel gating inhibition mediated by purinergic, opioidergic, and alpha-adrenergic autoreceptors. Few and contradictory data suggest also a role of beta-adrenergic autoreceptors (beta-ARs), the action of which, however, remains obscure. Here, using patch-perforated recordings, we show that rat chromaffin cells respond to the beta-AR agonist isoprenaline (ISO) by either upmodulating or downmodulating the amplitude of Ca(2+) currents through two distinct modulatory pathways. ISO (1 microm) could cause either fast inhibition (approximately 25%) or slow potentiation (approximately 25%), or a combination of the two actions. Both effects were completely prevented by propranolol. Slow potentiation was more evident in cells pretreated with pertussis toxin (PTX) or when beta(1)-ARs were selectively stimulated with ISO + ICI118,551. Potentiation was absent when the beta(2)-AR-selective agonist zinterol (1 microm), the protein kinase A (PKA) inhibitor H89, or nifedipine was applied, suggesting that potentiation is associated with a PKA-mediated phosphorylation of L-channels (approximately 40% L-current increase) through beta(1)-ARs. The ISO-induced inhibition was fast and reversible, preserved in cell treated with H89, and mimicked by zinterol. The action of zinterol was mostly on L-channels (38% inhibition). Zinterol action preserved the channel activation kinetics, the voltage-dependence of the I-V characteristic, and was removed by PTX, suggesting that beta(2)AR-mediated channel inhibition was mainly voltage independent and coupled to G(i)/G(o)-proteins. Sequential application of zinterol and ISO mimicked the dual action (inhibition/potentiation) of ISO alone. The two kinetically and pharmacologically distinct beta-ARs signaling uncover alternative pathways, which may serve the autocrine control of Ca(2+)-dependent exocytosis and other related functions of rat chromaffin cells.
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19
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Georget M, Mateo P, Vandecasteele G, Jurevicius J, Lipskaia L, Defer N, Hanoune J, Hoerter J, Fischmeister R. Augmentation of cardiac contractility with no change in L-type Ca2+ current in transgenic mice with a cardiac-directed expression of the human adenylyl cyclase type 8 (AC8). FASEB J 2002; 16:1636-8. [PMID: 12206999 DOI: 10.1096/fj.02-0292fje] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The beta-adrenergic cascade is severely impaired in heart failure (HF), in part because of a reduction in the activity of the two dominant cardiac adenylyl cyclase (AC) isoforms, AC5 and AC6. Hence, cardiac-directed AC overexpression is a conceivable therapeutic strategy in HF. In this study, we explored the consequences at the cellular and organ level of a cardiac-directed expression of the human AC8 in the transgenic mouse line AC8TG. Unlike AC5 and AC6, which are inhibited by intracellular Ca2+, AC8 is stimulated by Ca2+-calmodulin. Langendorff perfused hearts from AC8TG mice had a twofold higher left ventricular systolic pressure, a 40% faster heart rate, a 37% faster relaxation, and a 30% higher sensitivity to external Ca2+ than nontransgenic control mice (NTG). Cell shortening measured in isolated ventricular myocytes developed 22% faster and relaxed 43% faster in AC8TG than in NTG mice. Likewise, Ca2+ transients measured in fluo-3 AM-loaded myocytes were 30% higher and relaxed 24% faster in AC8TG compared with NTG mice. In spite of the large increase in Ca2+ transients and contraction, expression of AC8 had no effect on the whole-cell L-type Ca2+ current (ICa, L) amplitude. Moreover, ICa, L was unchanged even when AC8 was activated by raising intracellular Ca2+. Thus, cardiac expression of AC8 leads to an increase in cAMP that activates specifically Ca2+ uptake into the sarcoplasmic reticulum but not Ca2+ influx at the sarcolemma, suggesting a strong compartmentation of the cAMP signal.
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Affiliation(s)
- Marie Georget
- Laboratoire de Cardiologie Cellulaire et Moléculaire, INSERM U-446, Université Paris-Sud, Faculté de Pharmacie, F-92296 Châtenay-Malabry, France
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20
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Abstract
Efficacy has been defined in receptor pharmacology as a proportionality factor denoting the amount of physiological response a given ligand imparts to a biological system for a given amount of receptor occupancy. While first defined in terms of response, the concept can be expanded to a wide variety of G protein-coupled receptor (GPCR) behaviors, which includes pleiotropic interaction with multiple G proteins, internalization, oligomerization, desensitization, and interaction with membrane auxilliary proteins. Thus, there can be numerous types of efficacy, and different ligands can have a range of efficacies for different receptor behaviors. This review discusses the use of the efficacy concept in GPCR models based on the thermodynamic linkage theory and also in terms of the protein ensemble theory, in which macroaffinity of ligands for an ensemble of receptor microstates produces a new ligand-bound ensemble. The pharmacological characteristics of the ligand emerge from the intersection of the ligand-bound ensemble with the various ensembles defining pharmacological receptor behaviors. Receptor behaviors discussed are activation of G proteins; ability to be phosphorylated, desensitized, and internalized; formation of dimers and oligomers; and the interaction with auxiliary membrane and cytosolic proteins. The concepts of ligand-specific receptor conformation and conditional efficacy are also discussed in the context of ligand control of physiological response.
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Affiliation(s)
- Terry Kenakin
- GlaxoSmithKline Research and Development, Research Triangle Park, North Carolina 27709, USA.
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21
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Heubach JF, Graf EM, Molenaar P, Jäger A, Schröder F, Herzig S, Harding SE, Ravens U. Murine ventricular L-type Ca(2+) current is enhanced by zinterol via beta(1)-adrenoceptors, and is reduced in TG4 mice overexpressing the human beta(2)-adrenoceptor. Br J Pharmacol 2001; 133:73-82. [PMID: 11325796 PMCID: PMC1572761 DOI: 10.1038/sj.bjp.0704045] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The functional coupling of beta(2)-adrenoceptors (beta(2)-ARs) to murine L-type Ca(2+) current (I(Ca(L))) was investigated with two different approaches. The beta(2)-AR signalling cascade was activated either with the beta(2)-AR selective agonist zinterol (myocytes from wild-type mice), or by spontaneously active, unoccupied beta(2)-ARs (myocytes from TG4 mice with 435 fold overexpression of human beta(2)-ARs). Ca(2+) and Ba(2+) currents were recorded in the whole-cell and cell-attached configuration of the patch-clamp technique, respectively. 2. Zinterol (10 microM) significantly increased I(Ca(L)) amplitude of wild-type myocytes by 19+/-5%, and this effect was markedly enhanced after inactivation of Gi-proteins with pertussis-toxin (PTX; 76+/-13% increase). However, the effect of zinterol was entirely mediated by the beta(1)-AR subtype, since it was blocked by the beta(1)-AR selective antagonist CGP 20712A (300 nM). The beta(2)-AR selective antagonist ICI 118,551 (50 nM) did not affect the response of I(Ca(L)) to zinterol. 3. In myocytes with beta(2)-AR overexpression I(Ca(L)) was not stimulated by the activated signalling cascade. On the contrary, I(Ca(L)) was lower in TG4 myocytes and a significant reduction of single-channel activity was identified as a reason for the lower whole-cell I(Ca(L)). The beta(2)-AR inverse agonist ICI 118,551 did not further decrease I(Ca(L)). PTX-treatment increased current amplitude to values found in control myocytes. 4. In conclusion, there is no evidence for beta(2)-AR mediated increases of I(Ca(L)) in wild-type mouse ventricular myocytes. Inactivation of Gi-proteins does not unmask beta(2)-AR responses to zinterol, but augments beta(1)-AR mediated increases of I(Ca(L)). In the mouse model of beta(2)-AR overexpression I(Ca(L)) is reduced due to tonic activation of Gi-proteins.
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MESH Headings
- Adrenergic beta-1 Receptor Agonists
- Adrenergic beta-2 Receptor Agonists
- Adrenergic beta-Agonists/pharmacology
- Adrenergic beta-Antagonists/pharmacology
- Animals
- Barium/metabolism
- Binding Sites
- Calcium/metabolism
- Calcium Channels, L-Type/metabolism
- Electric Conductivity
- Ethanolamines/pharmacology
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- Heart Ventricles/cytology
- Heart Ventricles/drug effects
- Heart Ventricles/metabolism
- Humans
- Imidazoles/pharmacology
- Ion Channel Gating/drug effects
- Isoproterenol/antagonists & inhibitors
- Isoproterenol/pharmacology
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Transgenic
- Myocardium/cytology
- Myocardium/metabolism
- Pertussis Toxin
- Propanolamines/pharmacology
- Protein Binding
- Receptors, Adrenergic, beta-1/metabolism
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/metabolism
- Virulence Factors, Bordetella/pharmacology
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Affiliation(s)
- J F Heubach
- Institut für Pharmakologie und Toxikologie, Medizinische Fakultät Carl Gustav Carus der TU Dresden, D-01307 Dresden, Germany.
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22
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Zhou YY, Yang D, Zhu WZ, Zhang SJ, Wang DJ, Rohrer DK, Devic E, Kobilka BK, Lakatta EG, Cheng H, Xiao RP. Spontaneous activation of beta(2)- but not beta(1)-adrenoceptors expressed in cardiac myocytes from beta(1)beta(2) double knockout mice. Mol Pharmacol 2000; 58:887-94. [PMID: 11040034 DOI: 10.1124/mol.58.5.887] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Although ligand-free, constitutive beta(2)-adrenergic receptor (AR) signaling has been demonstrated in naive cell lines and in transgenic mice overexpressing cardiac beta(2)-AR, it is unclear whether the dominant cardiac beta-AR subtype, beta(1)-AR, shares the ability of spontaneous activation. In the present study, we expressed human beta(1)- or beta(2)-AR via recombinant adenoviral infection in ventricular myocytes isolated from beta(1)beta(2)-AR double knockout mice, creating pure beta(1)-AR and beta(2)-AR systems with variable receptor densities. A contractile response to a nonselective beta-AR agonist, isoproterenol, was absent in double knockout mouse myocytes but was fully restored after adenoviral beta(1)-AR or adenoviral beta(2)-AR infection. Increasing the titer of adenoviral vectors (multiplicity of infection 10-1000) led to a dose-dependent expression of beta(1)- or beta(2)-AR with a maximal density of 1207 +/- 173 (36-fold over the wild-type control value) and 821+/-38 fmol/mg protein (69-fold), respectively. Using confocal immunohistochemistry, we directly visualized the cellular distribution of beta(1)-AR and beta(2)-AR and found that both subtypes were distributed on the cell surface membrane and transverse tubules, resulting in a striated pattern. In the absence of ligand, beta(2)-AR expression resulted in graded increases in baseline cAMP and contractility up to 428% and 233% of control, respectively, at the maximal beta(2)-AR density. These effects were specifically reversed by a beta(2)-AR inverse agonist, ICI 118,551 (10(-7) M). In contrast, overexpression of beta(1)-AR, even at a greater density, failed to enhance either basal cAMP or contractility; the alleged beta(1)-AR inverse agonist, CGP 20712A (10(-6) M), had no significant effect on basal contraction in these cells. Thus, we conclude that acute beta(2)-AR overexpression in cardiac myocytes elicits significant physiological responses due to spontaneous receptor activation; however, this property is beta-AR subtype specific because beta(1)-AR does not exhibit agonist-independent spontaneous activation.
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Affiliation(s)
- Y Y Zhou
- Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
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23
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Zhou YY, Wang SQ, Zhu WZ, Chruscinski A, Kobilka BK, Ziman B, Wang S, Lakatta EG, Cheng H, Xiao RP. Culture and adenoviral infection of adult mouse cardiac myocytes: methods for cellular genetic physiology. Am J Physiol Heart Circ Physiol 2000; 279:H429-36. [PMID: 10899083 DOI: 10.1152/ajpheart.2000.279.1.h429] [Citation(s) in RCA: 220] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Rapid development of transgenic and gene-targeted mice and acute genetic manipulation via gene transfer vector systems have provided powerful tools for cardiovascular research. To facilitate the phenotyping of genetically engineered murine models at the cellular and subcellular levels and to implement acute gene transfer techniques in single mouse cardiomyocytes, we have modified and improved current enzymatic methods to isolate a high yield of high-quality adult mouse myocytes (5.3 +/- 0.5 x 10(5) cells/left ventricle, 83.8 +/- 2.5% rod shaped). We have also developed a technique to culture these isolated myocytes while maintaining their morphological integrity for 2-3 days. The high percentage of viable myocytes after 1 day in culture (72.5 +/- 2.3%) permitted both physiological and biochemical characterization. The major functional aspects of these cells, including excitation-contraction coupling and receptor-mediated signaling, remained intact, but the contraction kinetics were significantly slowed. Furthermore, gene delivery via recombinant adenoviral infection was highly efficient and reproducible. In adult beta(1)/beta(2)-adrenergic receptor (AR) double-knockout mouse myocytes, adenovirus-directed expression of either beta(1)- or beta(2)-AR, which occurred in 100% of cells, rescued the functional response to beta-AR agonist stimulation. These techniques will permit novel experimental settings for cellular genetic physiology.
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MESH Headings
- Adenoviridae
- Animals
- Calcium/metabolism
- Cell Culture Techniques/methods
- Cell Membrane/physiology
- Cells, Cultured
- Female
- Gene Transfer Techniques
- Heart Ventricles
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Inbred DBA
- Mice, Inbred Strains
- Mice, Knockout
- Myocardium/cytology
- Myocardium/metabolism
- Receptors, Adrenergic, beta-1/deficiency
- Receptors, Adrenergic, beta-1/genetics
- Receptors, Adrenergic, beta-1/physiology
- Receptors, Adrenergic, beta-2/deficiency
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/physiology
- Transfection/methods
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Affiliation(s)
- Y Y Zhou
- Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224, USA
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24
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Zhou YY, Song LS, Lakatta EG, Xiao RP, Cheng H. Constitutive beta2-adrenergic signalling enhances sarcoplasmic reticulum Ca2+ cycling to augment contraction in mouse heart. J Physiol 1999; 521 Pt 2:351-61. [PMID: 10581307 PMCID: PMC2269668 DOI: 10.1111/j.1469-7793.1999.00351.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
1. Transgenic overexpression of the beta2-adrenergic receptor (beta2AR) in mouse heart augments baseline cardiac function in a ligand-independent manner, due to the presence of spontaneously active beta2AR (beta2AR*). This study aims to elucidate the mechanism of beta2AR*-mediated modulation of cardiac excitation-contraction (EC) coupling. 2. Confocal imaging was used to analyse Ca2+ sparks and spatially resolve Ca2+ transients in single ventricular myocytes from transgenic (TG4) and non-transgenic (NTG) littermates. Whole-cell voltage- and current-clamp techniques were used to record L-type Ca2+ currents (ICa) and action potentials, respectively. 3. In the absence of any beta2AR ligand, TG4 myocytes had greater contraction amplitudes, larger Ca2+ transients and faster relaxation times than did NTG cells. 4. The action potentials of TG4 and NTG myocytes were similar, except for a prolonged end-stage repolarization in TG4 cells; the ICa density and kinetics were nearly identical. The relationship between peak Ca2+ and contraction, which reflects myofilament Ca2+ sensitivity, was similar. 5. In TG4 cells, the frequency of Ca2+ sparks (spontaneous or evoked at -40 mV) was 2-7 times greater, despite the absence of change in the resting Ca2+, sarcoplasmic reticulum (SR) Ca2+ content, and ICa. Individual sparks were brighter, broader and lasted longer, leading to a 2.3-fold greater signal mass. Thus, changes in both spark frequency and size underlie the greater Ca2+ transient in TG4 cells. 6. The inverse agonist ICI 118,551 (ICI, 5 x 10-7 M), which blocks spontaneous beta2AR activation, reversed the aforementioned beta2AR* effects on cardiac EC coupling without affecting the sarcolemmal ICa. However, ICI failed to detect significant constitutive beta2AR activity in NTG cells. 7. We conclude that beta2AR*-mediated signalling enhances SR release channel activity and Ca2+-induced Ca2+ release in TG4 cardiac myocytes, and that beta2AR* enhances EC coupling by reinforcing SR Ca2+ cycling (release and reuptake), but bypassing the sarcolemmal ICa.
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Affiliation(s)
- Y Y Zhou
- Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
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25
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Abstract
Recent studies have added complexities to the conceptual framework of cardiac beta-adrenergic receptor (beta-AR) signal transduction. Whereas the classical linear G(s)-adenylyl cyclase-cAMP-protein kinase A (PKA) signaling cascade has been corroborated for beta(1)-AR stimulation, the beta(2)-AR signaling pathway bifurcates at the very first postreceptor step, the G protein level. In addition to G(s), beta(2)-AR couples to pertussis toxin-sensitive G(i) proteins, G(i2) and G(i3). The coupling of beta(2)-AR to G(i) proteins mediates, to a large extent, the differential actions of the beta-AR subtypes on cardiac Ca(2+) handling, contractility, cAMP accumulation, and PKA-mediated protein phosphorylation. The extent of G(i) coupling in ventricular myocytes appears to be the basis of the substantial species-to-species diversity in beta(2)-AR-mediated cardiac responses. There is an apparent dissociation of beta(2)-AR-induced augmentations of the intracellular Ca(2+) (Ca(i)) transient and contractility from cAMP production and PKA-dependent cytoplasmic protein phosphorylation. This can be largely explained by G(i)-dependent functional compartmentalization of the beta(2)-AR-directed cAMP/PKA signaling to the sarcolemmal microdomain. This compartmentalization allows the common second messenger, cAMP, to perform selective functions during beta-AR subtype stimulation. Emerging evidence also points to distinctly different roles of these beta-AR subtypes in modulating noncontractile cellular processes. These recent findings not only reveal the diversity and specificity of beta-AR and G protein interactions but also provide new insights for understanding the differential regulation and functionality of beta-AR subtypes in healthy and diseased hearts.
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MESH Headings
- Adrenergic beta-Agonists/pharmacology
- Adrenergic beta-Antagonists/pharmacology
- Animals
- Calcium/physiology
- Cyclic AMP/physiology
- Cyclic AMP-Dependent Protein Kinases/physiology
- Dogs
- GTP-Binding Proteins/physiology
- Heart/drug effects
- Heart/physiology
- Heart Failure/metabolism
- Humans
- Hydrogen-Ion Concentration
- Mice
- Mice, Transgenic
- Muscle Proteins/drug effects
- Muscle Proteins/physiology
- Myocardial Contraction/drug effects
- Myocardial Contraction/physiology
- Myocardium/metabolism
- Phosphorylation/drug effects
- Protein Processing, Post-Translational/drug effects
- Rats
- Receptors, Adrenergic, beta-1/drug effects
- Receptors, Adrenergic, beta-1/physiology
- Receptors, Adrenergic, beta-2/classification
- Receptors, Adrenergic, beta-2/drug effects
- Receptors, Adrenergic, beta-2/physiology
- Signal Transduction/drug effects
- Signal Transduction/physiology
- Species Specificity
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Affiliation(s)
- R P Xiao
- Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, Baltimore, MD 21224, USA.
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