Identification and Functional Role ofβ-adrenergic Receptor Subtypes in Primate and Rodent:In Vivoversus Isolated Myocytes

doi:10.1006/jmcc.1996.0121

Journal of Molecular and Cellular Cardiology

Volume 28, Issue 6, June 1996, Pages 1307-1317

https://doi.org/10.1006/jmcc.1996.0121 Get rights and content

Abstract

We determined the relationship between theβ₁- andβ₂-adrenergic receptor subtypes in isolated myocytes and their physiological responsiveness in chronically instrumented conscious baboons and rats. In conscious baboons, isoproterenol (ISO) (0.02μg/kg) increased left ventricular (LV) dP/dtby 89±6.7% from 2898±370 mmHg/s and only by 13±3.3% from 2491±146 mmHg/s afterβ₁-adrenergic receptor blockade, indicating that the predominant physiological response was mediated byβ₁-adrenergic receptors. Decreases in mean arterial pressure (−11±0.5 mmHgv−16±4.6 mmHg) and coronary vascular resistance (−3.1±0.4v−3.6±0.4 mmHg/ml/min) induced by ISO were not different before and afterβ₁-blockade, indicating thatβ₂-adrenergic receptors were not blocked. In conscious rats, ISO (0.4μg/kg) increased LV dP/dtby 50±4.9% from 13 252±2002 mmHg/s and only by 10±3.9% from 10 793±1364 mmHg/s afterβ₁-adrenergic receptor blockade; whereas decreases in mean arterial pressure induced by ISO were not different before and afterβ₁blockade (−19±2.4 mmHgv−16±2.2 mmHg), i.e. very consistent with the physiological responses in baboons.In vitrostudies of isolated myocytes, using radioligand binding with¹²⁵I-cyanopindolol (¹²⁵I-cyp) and the subtypeβ₁-selective antagonist betaxolol and theβ₂-selective antagonist ICI 118 551 indicated that theβ₁/β₂ratio of rat myocytes was 92/8; whereas baboon myocytes were more equally distributed (59/41). Thus, in both species the preponderance of effects of ISO on ventricular function wasβ₁-adrenergic receptor mediated, which is consistent with theβ₁/β₂ratio in rat myocytes but not in baboon myocytes, where a significant fraction ofβ₂-adrenergic receptors does not appear to exert an effect on conctractilityin vivo.

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Cited by (23)

Remodelling of potassium currents underlies arrhythmic action potential prolongation under beta-adrenergic stimulation in hypertrophic cardiomyopathy
2022, Journal of Molecular and Cellular Cardiology
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β-ARS models are largely based on data from other species, reparametrized to human cardiomyocytes. Therefore, differences on distinct ion channel conformations [52], different molecular processes involved in β-ARS [29,53], or distinct densities and locations of β-ARS receptors [54], require further investigations. Data availability regarding myosin binding protein-C and titin phosphorylation [55] would enable implementing these targets in the β-ARS model, qualifying it for quantitative investigations of β-ARS response in active tension.
Hypertrophic cardiomyopathy (HCM) patients often present an enhanced arrhythmogenicity that can lead to lethal arrhythmias, especially during exercise. Recent studies have indicated an abnormal response of HCM cardiomyocytes to β-adrenergic receptor stimulation (β-ARS), with prolongation of their action potential rather than shortening. The mechanisms underlying this aberrant response to sympathetic stimulation and its possible proarrhythmic role remain unknown. The aims of this study are to investigate the key ionic mechanisms underlying the HCM abnormal response to β-ARS and the resultant repolarisation abnormalities using human-based experimental and computational methodologies. We integrated and calibrated the latest models of human ventricular electrophysiology and β-ARS using experimental measurements of human adult cardiomyocytes from control and HCM patients. Our major findings include: (1) the developed in silico models of β-ARS capture the behaviour observed in the experimental data, including the aberrant response of HCM cardiomyocytes to β-ARS; (2) the reduced increase of potassium currents under β-ARS was identified as the main mechanism of action potential prolongation in HCM, rather than a more sustained inward calcium current; (3) action potential duration differences between healthy and HCM cardiomyocytes were increased upon β-ARS, while endocardial to epicardial differences in HCM cardiomyocytes were reduced; (4) models presenting repolarisation abnormalities were characterised by downregulation of the rapid delayed rectifier potassium current and the sodium‑potassium pump, while inward currents were upregulated. In conclusion, our results identify causal relationships between the HCM phenotype and its arrhythmogenic response to β-ARS through the downregulation of potassium currents.
Use of beta-blockers for the treatment of cardiac arrest due to ventricular fibrillation/pulseless ventricular tachycardia: A systematic review
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There are several differences in β-receptors between species, as well as cardiac function and response to CPR procedures.50 There are marked differences, for example, among the proportion of β1 and β2-receptors,51,52 which could account for diverging results in some of the studies cited, namely in the reports from Strohmenger et al.30 and Hilwig et al.11 It is noteworthy that, even though these studies failed to show a benefit on the use of beta-blockers during CPR, both of them indicate that it is a safe strategy and seem not to change the outcome of CPR.11,30 Even so, many evidences have been accumulating over the years, with elucidation of many mechanisms behind the benefits of β-blockade during CPR.
Advanced Life Support guidelines recommend the use of epinephrine during Cardiopulmonary Resuscitation (CPR), as to increase coronary blood flow and perfusion pressure through its alpha-adrenergic peripheral vasoconstriction, allowing minimal rises in coronary perfusion pressure to make defibrillation possible. Contrasting to these alpha-adrenergic effects, epinephrine's beta-stimulation may have deleterious effects through an increase in myocardial oxygen consumption and a reduction of subendocardial perfusion, leading to postresuscitation cardiac dysfunction.
The present paper consists of a systematic review of the literature regarding the use of beta-blockade in cardiac arrest due to ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT).
Studies were identified through MEDLINE electronic databases research and were included those regarding the use of beta-blockade during CPR.
Beta-blockade has been extensively studied in animal models of CPR. These studies not only suggest that beta-blockade could reduce myocardial oxygen requirements and the number of shocks necessary for defibrillation, but also improve postresuscitation myocardial function, diminish arrhythmia recurrences and prolong survival. A few case reports described successful beta-blockade use in patients, along with two prospective human studies, suggesting that it could be safe and effectively used during cardiac arrest in humans.
Even though the existing literature points toward a beneficial effect of beta-blockade in patients presenting with cardiac arrest due to VF/pulseless VT, high quality human trials are still lacking to answer this question definitely.
The increase in rat ventricular automaticity induced by salbutamol is mediated through β<inf>1</inf>- but not β<inf>2</inf>-adrenoceptors: Role of phosphodiesterases
2011, Life Sciences
Citation Excerpt :
Differences in functions and density of β-AR among species have been reported. For example, β2-AR density is higher in primate than in rodent myocardium (Cui et al., 1996). Also, direct β2-AR activation enhances contractility in human myocardium (Schäfers et al., 1994), but in rodents β2-AR stimulation only increase cardiac inotropy after inhibition of PDEs (Gonzalez-Muñoz et al., 2009) or Gi protein (Xiao et al., 1995).
While β₂-adrenoceptor (AR) agonists are useful bronchodilators, they also produce cardiac arrhythmias. These agents are not fully selective and also activate β₁-AR, but the involvement of β₁-AR and β₂-AR in the observed pro-arrhythmic effect has not been established. We studied the effect of β₁-AR and β₂-AR activation on ventricular automaticity and the role of phosphodiesterases (PDE) in regulating this effect.
Experiments were performed in the spontaneously beating isolated right ventricle of the rat heart. We also measured cAMP production in this tissue.
The β₂-AR agonist salbutamol (1-100 μM) produced a concentration-dependent increase in ventricular automaticity that was not affected by 50 nM of the β₂-AR antagonist ICI 118551. This effect was enhanced by the non-selective PDE inhibitor theophylline (100 μM) and by the selective PDE4 inhibitors rolipram (1 μM) and Ro 201724 (2 μM), but not modified by the selective PDE3 inhibitors cilostamide (0.3 μM) or milrinone (0.2 μM). The effects of salbutamol alone and in the presence of either theophylline or rolipram were virtually abolished by 0.1 μM β₁-AR antagonist CGP20712A. Salbutamol (10 μM) increased the cAMP concentration, and this effect was abolished by CGP 20712A (0.1 μM) but enhanced by theophylline (100 μM) or rolipram (1 μM). Cilostamide (0.3 μM) failed to modify the effect of salbutamol on cAMP concentration.
These results indicate that the increase of ventricular automaticity elicited by salbutamol was exclusively mediated through β₁-AR and enhanced by non-selective PDE inhibition with theophylline or selective PDE4 inhibition. However, PDE3 did not appear to regulate this effect.
The potential beneficial effects of beta adrenergic blockade in the treatment of ventricular fibrillation
2009, European Journal of Pharmacology
Cardiac arrest remains a major medical emergency in Western societies, with ventricular fibrillation being the initial rhythm in a significant proportion of cases. Adrenaline is generally accepted to improve the resuscitation outcome, since it improves coronary and cerebral blood flow during cardiopulmonary resuscitation, but several detrimental effects have been associated with its use, most of which are thought to be mediated by its beta adrenergic properties. Several animal studies suggest that beta adrenergic blockade during resuscitation, is associated with increased rates of resuscitation and improved post-resuscitation myocardial function. This article reviews the presence and function of β-adrenoceptor subtypes in the intact and diseased human myocardium, as well as the differences observed in β₁- and β₂ adrenoceptor subtypes in different species.
Late-stage alterations in myofibrillar contractile function in a transgenic mouse model of dilated cardiomyopathy (Tgαq*44)
2008, Journal of Molecular and Cellular Cardiology
Citation Excerpt :
Surprisingly, the observed increased Ca2+sensitivity of force production suggested a deficit of PKA-mediated intracellular phosphorylation rather than PKC activation during the development of DCM in this model. Differences in the expression and phosphorylation levels of contractile proteins and β-receptor coupling of rodent and human hearts [25–27] limit direct extrapolation of our model experiments to humans. Nevertheless, the decreased PKA-mediated contractile protein phosphorylation is in accordance with a number of independent investigations on DCM in humans, and thereby points to a possible role of decreased PKA activation in the pathogenesis of DCM.
Mechanical and biochemical alterations were investigated in permeabilized cardiomyocytes along with the progression of dilated cardiomyopathy (DCM) in a transgenic mouse line overexpressing the activated Gαq protein (Tgαq*44). The isometric force, its Ca²⁺ sensitivity (pCa₅₀) and the turnover rate of the actin–myosin cycle (k_tr) were determined at sarcomere lengths (SLs) of 1.9 μm and 2.3 μm before (at 4 and 10 months of age) and after hemodynamic decompensation (at 14 and 18 months of age) in Tgαq*44 cardiomyocytes and in age-matched control cardiomyocytes. The SL-dependence of pCa₅₀ was not different in Tgαq*44 and control hearts. In contrast, a significant increase in pCa₅₀ was observed in the Tgαq*44 cardiomyocytes (ΔpCa₅₀: 0.10–0.15 vs. the controls) after 10 months of age that could be diminished by exposures to the catalytic subunit of protein kinase A (PKA). Accordingly, a decline in endogenous PKA activity and decreased troponin I phosphorylation were detected after 10 months in the Tgαq*44 hearts. Finally, the maximal Ca²⁺-activated force (F_o) and k_tr were lower and the passive force (F_passive) was higher at 18 months in the Tgαq*44 cardiomyocytes compared to the control. These mechanical alterations were paralleled by a robust increase in β-myosin heavy chain expression in the Tgαq*44 hearts. In conclusion, our data suggested that an initial decrease of PKA signaling and subsequent changes in myofilament protein expression may contribute to the development of dilated cardiomyopathy in Tgαq*44 hearts.
Loss of β-adrenoceptor response in myocytes overexpressing the Na <sup>+</sup>/Ca<sup>2+</sup>-exchanger
2004, Journal of Molecular and Cellular Cardiology
Increased Na⁺/Ca²⁺-exchanger (NCX) and altered β-adrenoceptor (βAR) responses are observed in failing human heart. To determine the possible interaction between these changes, we investigated the effect of NCX overexpression on responses to isoproterenol in adult rat ventricular myocytes. Responses to isoproterenol were largely mediated through the β₁AR in control myocytes. Adenovirally-mediated overexpression of NCX, at levels, which did not alter basal contraction of myocytes, markedly depressed the isoproterenol concentration–response curve. Responses to isoproterenol could be restored to normal by β₂AR blockade, suggesting a β₂AR-mediated inhibition of β₁AR signalling. Pertussis toxin normalised isoproterenol responses in NCX cells, indicating that β₂AR effects were mediated by Gi. Negative-inotropic effects of high concentrations of ICI 118,551, previously shown to be due to β₂AR–Gi coupling, were increased in NCX cells. We conclude that NCX upregulation can markedly alter the consequences of βAR stimulation and that this may contribute to the alterations in βAR response seen in failing human heart.

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^☆: Please address all correspondence to: Dorothy E. Vatner, New England Regional Primate Research Center, One Pine Hill Drive, Southborough, MA 01772-9102, USA.

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Regular PaperIdentification and Functional Role ofβ-adrenergic Receptor Subtypes in Primate and Rodent:In Vivoversus Isolated Myocytes☆

Abstract

Regular Paper
Identification and Functional Role ofβ-adrenergic Receptor Subtypes in Primate and Rodent:In Vivoversus Isolated Myocytes☆