Regulation of alpha 1-, beta 1-, and beta 2-adrenergic receptors in rat heart by norepinephrine

1996 ◽  
Vol 271 (5) ◽  
pp. H1762-H1768 ◽  
Author(s):  
M. Zhao ◽  
H. K. Hagler ◽  
K. H. Muntz
Keyword(s):  
Adrenergic Receptors ◽  
Ventricular Myocytes ◽  
Plasma Catecholamine ◽  
Elevated Plasma ◽  
Atrial Myocytes ◽  
Rat Hearts ◽  
Chronic Infusion ◽  
Beta 2 ◽  
Set Up ◽  
Tissue Compartments

Previous studies suggest that the desensitization and downregulation of beta 1-adrenergic receptors (beta 1-AR) in the failing heart are the result of the elevated plasma catecholamine levels associated with this disease. To examine norepinephrine (NE)-induced regulation of cardiac adrenergic receptors, rats were infused with l-NE (200 micrograms.kg-1.h-1 for 7 days) or vehicle (0.001 N HCl) by implantation of osmotic minipumps. The technique of coverslip autoradiography was used to quantify alpha 1-adrenergic receptors (alpha 1-AR), beta 1-AR, and beta 2-AR in different tissue compartments of rat hearts. For measurement of beta-AR binding, sections were incubated with 70 pM [125I]iodocyanopindolol (ICYP) alone or in the presence of 5 microM dl-propranolol or 5 x 10(-7) M CGP-20712A (a beta 1-antagonist) and then set up for autoradiography. [3H]prazosin (1 nM) with or without phentolamine was used to study alpha-AR binding. Chronic infusion of NE induced a greater downregulation of beta 2-AR compared with beta 1-AR in all regions studied, including atrial and ventricular myocytes, coronary arterioles, and connective tissue. An 18% loss of beta 1-AR was seen only in atrial myocytes; beta 1-AR density actually increased 28% in ventricular myocytes following NE infusion. There was a 15% decrease in alpha 1-AR in ventricular myocytes, whereas no change in alpha 1-AR density was seen in myocardial arterioles. Our study demonstrates that beta 2-AR are more susceptible to NE-induced downregulation than beta 1-AR. Thus other mechanisms may be involved in the selective downregulation of beta 1-AR in certain forms of heart failure.

P3830Carvedilol treatment diminishes spontaneous calcium release and electrical activity in human atrial myocytes

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
V Jimenez-Sabado ◽  
T Lu ◽  
S Casabella ◽  
C Tarifa ◽  
A Herraiz-Martinez ◽  
...  
Keyword(s):  
Electrical Activity ◽  
Adrenergic Receptors ◽  
Calcium Release ◽  
Calcium Waves ◽  
Atrial Myocytes ◽  
Patch Clamp Technique ◽  
Human Atrial Myocytes ◽  
Site Density ◽  
Inward Currents ◽  
Beta 2

Abstract Background Atrial fibrillation (AF) has been associated with an increase in spontaneous calcium release induced electrical activity, which could potentially be reversed by carvedilol, a nonselective beta-blocker that also inhibits the cardiac ryanodine receptor (RyR2). Interestingly the enantiomer R-carvedilol inhibits the RyR2 but not beta-adrenergic receptors, allowing it to effectively prevent calcium release-induced spontaneous electrical activity without inducing bradycardia and hypotension. Purpose The purpose of this study was to determine how carvedilol treatment affects calcium release-induced transient inward currents (ITI) in human atrial myocytes from patients with AF; and to test the effects of R-carvedilol on spontaneous calcium release in order to assess its therapeutical utility. Methods Human atrial myocytes were isolated from patients undergoing cardiac surgery and subjected to patch-clamp technique (n=60) or confocal calcium imaging (n=6). Beta-2 adrenergic receptors were activated with the selective agonist fenoterol (3μM) and 1μM R-carvedilol was used to inhibit spontaneous calcium release events. Results Recordings of calcium release-induced transient inward currents (ITI) revealed that carvedilol treatment reduced the ITI frequency in patients with AF from 2.2±0.4 events/min in untreated patients to 0.59±0.35 events/min (p<0.01), which was even lower than the incidence in patients without AF (1.0±0.1 events/min; p<0.01). To assess the effects of R-carvedilol, myocytes were first simulated with fenoterol. This increased the calcium spark frequency from 23±15 to 960±336 events/s/1000μm2 in 16 cells from 6 patients (p<0.05). This was due to an increase in the spark site density (from 0.50±0.24 to 12.1±2.4 sites/1000μm2, p<0.001) rather than in the firing rate (0.068±0.14 vs. 0.035±0.012 sparks/s in control, p=0.14). Fenoterol also increased the spark duration from 50.9±5.4 to 77.3±4.1ms (p<0.001) without affecting the amplitude. Importantly, fenoterol also induced global calcium release events such as calcium waves and transients (2.8±1.1 vs. 0 events/min in control, p<0.05). When R-carvedilol was added, the effects of fenoterol were abolished, reducing the incidence of calcium sparks to 69±51 events/s/1000μm2 (p<0.05), the spark site density to 1.68±1.04 sites/1000μm2 (p<0.01), the spark duration to 63.4±4.3ms (p<0.05), and calcium waves and transients were reduced to 0.21±0.14 events/min (p<0.05). Conclusions Carvedilol treatment reduces the ITI frequency in patients with AF to levels below that observed at baseline in patients without AF. Furthermore, the non-beta-blocking R-carvedilol enantiomer abolishes spontaneous calcium release events induced by beta-2 adrenergic stimulation in human atrial myocytes, proposing a therapeutical utility for this compound in patients with AF linked to excessive spontaneous calcium release. Acknowledgement/Funding SAF2017-88019; Marato2015-20-30; SGR2017-1769; CIBERCV

Beta 2-adrenergic receptors enhance contractility by stimulating HCO3(-)-dependent intracellular alkalinization

1997 ◽  
Vol 273 (2) ◽  
pp. H1044-H1047 ◽  
Author(s):  
T. Jiang ◽  
S. F. Steinberg
Keyword(s):  
Intracellular Ph ◽  
Adrenergic Receptors ◽  
Ventricular Myocytes ◽  
Electrical Field Stimulation ◽  
Inotropic Response ◽  
Signaling Mechanism ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Beta 2 ◽  
Intracellular Alkalinization

Previous studies established that beta 2-adrenergic receptors enhance the amplitude, without abbreviating the kinetics, of the twitch in adult rat ventricular myocytes. The present study was designed to identify the dominant signaling mechanism mediating this response. Myocytes from adult rat ventricles were loaded with the pH-sensitive fluorophore 2',7'-bis(carboxyethyl)-5(6')-carboxyfluorescein, and simultaneous measurements of intracellular pH and contraction were performed during electrical field stimulation under basal conditions and after stimulation with isoproterenol or the selective beta 2-receptor agonist zinterol. Inhibition of protein kinase A with H-7 completely inhibited the isoproterenol-dependent, but not the zinterol-dependent, positive inotropic response. The effect of zinterol to increase twitch amplitude was associated with an alkalinization of 0.07 +/- 0.02 pH unit, which was not prevented by inhibition of the Na+/H+ exchanger with hexamethylene-amiloride. Rather, removal of bicarbonate from the extracellular buffer prevented the beta 2-receptor-dependent alkalinization as well as the positive inotropic response. These results indicate that beta 2-adrenergic receptors induce a positive inotropic response in adult rat ventricular myocytes via a adenosine 3',5'-cyclic monophosphate-independent mechanism that involves intracellular alkalinization due to activation of a bicarbonate-dependent intracellular pH regulatory mechanism.

Treatment with beta-blockers normalizes RyR2 phosphorylation and calcium spark activity in atrial myocytes from patients with atrial fibrillation

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
V Jimenez-Sabado ◽  
S Casabella ◽  
P Izquierdo ◽  
C Tarifa ◽  
A Llach ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Calcium Imaging ◽  
Adrenergic Receptors ◽  
Beta Blockers ◽  
Funding Source ◽  
Atrial Myocytes ◽  
Calcium Sparks ◽  
Beta Adrenergic ◽  
Calcium Spark ◽  
Confocal Calcium Imaging

Abstract Background Atrial fibrillation has been associated with an increase in ryanodine receptor (RyR2) phosphorylation and local calcium release (calcium sparks). Carvedilol, a nonselective beta-adrenergic receptor blocker also inhibits the cardiac ryanodine receptor (RyR2), but it has been suggested that the enantiomer R-carvedilol only inhibits RyR2 activity and hence has the potential to inhibit calcium sparks without affecting RyR2 phosphorylation. Purpose This study aimed to determine the ability of the enantiomers R- and S-carvedilol to reverse RyR2 phosphorylation at s2808 and calcium sparks induced by the β2-adrenergic agonist fenoterol, in order to determine the relationship between RyR2 phosphorylation at s2808 and calcium spark frequency, and to assess the efficacy of R- and S-carvedilol. Methods Human right atrial myocytes were isolated and subjected to immunofluorescent labelling of total and s2808 phosphorylated RyR2, or loaded with fluo-4 and subjected to confocal calcium imaging. Beta-adrenergic receptors were first activated with 3μM fenoterol and then inhibited by different concentrations of carvedilol R- or S-enantiomers. Results Incubation of myocytes with fenoterol increased the s2808/RyR2 ratio from 0.32±0.03 to 0.66±0.05 (n=18, p&lt;0.001). Incubation with 0.1, 0.3, 1 or 3μM R-carvedilol in the presence of fenoterol changed the s2808/RyR2 ratio to 0.64±0.05, 0.44±0.04, 0.34±0.07 and 0.28±0.05 (p&lt;0.01) respectively. For comparison 3μM S-carvedilol reduced the s2808/RyR2 ratio to 0.23±0.06 in myocytes from 5 patients (p&lt;0.01). Confocal calcium imaging revealed that fenoterol increased the spark density from 0.28±0.04 to 1.24±0.25 events/s/1000μm2 (n=9, p&lt;0.01) and addition of 0.1, 0.3, or 1μM R-carvedilol changed the frequency to 1.32±0.52, 0.38±0.05, and 0.15±0.05 events/s/1000μm2 (p&lt;0.01) respectively. Analysis of atrial myocytes from patients without atrial fibrillation revealed that the s2808/RyR2 ratio was similar in 25 patients treated with beta-blockers (0.39±0.04) and 57 that did not receive beta-blockers (0.44±0.03, p=0.33) while the s2808/RyR2 ratio was significantly smaller in 16 patients with atrial fibrillation receiving beta-blockers (0.43±0.08) than in 5 patients that did not (0.80±0.19, p&lt;0.05). Conclusions R-carvedilol reverses the effects of beta-adrenergic stimulation on s2808 phosphorylation and calcium sparks in human atrial myocytes, and treatment with beta-blockers reduces excessive RyR2 phosphorylation at s2808 in patients with atrial fibrillation to levels observed in those without the arrhythmia, pointing to beta-adrenergic receptors as a target for controlling RyR2 phophorylation and activity in atrial fibrillation. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Spanish Ministry of Science and Innovation & Spanish Ministry of Health and Consume

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