scholarly journals Cross-talk between cAMP and Ca2+ signalling in cardiac pacemaker cells involves IP3-evoked Ca2+ release and stimulation of adenylyl cyclase 1

2022 ◽  
Author(s):  
Samuel J Bose ◽  
Matthew Read ◽  
Rebecca A Capel ◽  
Emily Akerman ◽  
Thamali Ayagama ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Calcium Release ◽  
Cardiac Pacemaker ◽  
Calcium Transient ◽  
Right Atrial ◽  
Pacemaker Activity ◽  
Intact Mouse ◽  
Atrial Tissue ◽  
Adrenoceptor Agonist ◽  
Beating Rate

Atrial arrhythmias, such as atrial fibrillation (AF), are a major mortality risk and a leading cause of stroke. The IP3 signalling pathway has been proposed as an atrial specific target for AF therapy, and atrial IP3 signalling has been linked to the activation of calcium sensitive adenylyl cyclases AC1 and AC8. Here we investigated the involvement of AC1 in the response of intact mouse atrial tissue and isolated guinea pig atrial and sinoatrial node (SAN) cells to the α-adrenoceptor agonist phenylephrine (PE) using the selective AC1 inhibitor ST034307. The maximum rate change of spontaneously beating mouse right atrial tissue exposed to PE was reduced from 14.46 % to 8.17% (P = 0.005) in the presence of 1 μM ST034307, whereas the increase in tension generated in paced left atrial tissue in the presence of PE was not inhibited by ST034307 (Control = 14.20 %, ST034307 = 16.32 %; P > 0.05). Experiments were performed using isolated guinea pig atrial and SAN cells loaded with Fluo-5F-AM to record changes in calcium transient amplitude (CaT) generated by 10μM PE in the presence and absence of 1μM ST034307. ST034307 significantly reduced the beating rate of SAN cells (0.34-fold decrease; P = 0.004), but did not result in an inhibition of CaT amplitude increase in response to PE in atrial cells. The results presented here demonstrate the involvement of AC1 in the downstream response of atrial pacemaker activity to α-adrenoreceptor stimulation and IP3R calcium release.

PDE4B and PDE4D differentially regulate cardiac pacemaker activity

EP Europace ◽  
2021 ◽  
Vol 23 (Supplement_3) ◽  
Author(s):  
WPV Pereira De Vasconcelos ◽  
AMG Gomez ◽  
RF Fischmeister ◽  
GV Vandecasteele ◽  
DM Mika
Keyword(s):  
Ventricular Myocytes ◽  
Cardiac Pacemaker ◽  
Hydrolytic Activity ◽  
Pde4 Inhibitor ◽  
Pacemaker Activity ◽  
National Budget ◽  
Beating Rate ◽  
Public Grant

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Agence Nationale de la Recherche (ANR) Background Heart rate (HR) is generated by spontaneous electrical activity in the sinoatrial node (SAN) and is modulated by the autonomic nervous system. During sympathetic stimulation, the activation of β-adrenergic receptors (βAR) increases cAMP levels, leading to positive chronotropic effect. Among the 6 cardiac cAMP-PDE families, PDE4 is critical for controlling excitation-contraction coupling (ECC) during β-stimulation in atrial and ventricular myocytes. PDE4 may also be important for automaticity. 3 genes encode for PDE4 in the heart (pde4a, 4b, 4d). We propose to investigate their respective contribution to the regulation of pacemaker activity.  Methods Total PDE activity in mouse SAN was determined as the cAMP-hydrolytic activity measured in the absence of PDE inhibitor and the fraction corresponding to PDE4 activity was assessed by including the PDE4 inhibitor Ro-20-1724. The in vitro pacemaker activity was assessed by measuring spontaneous Ca2+ transients in Fluo4-loaded-SAN tissue from wild-type (WT) and PDE4KO mice. Images were obtained using confocal microscopy. Telemetry EKG was recorded in conscious mice in control (CTRL) conditions, after pharmacological denervation with atropine (1 mg/kg) and propranolol (2 mg/kg) and after β-stimulation with isoproterenol (ISO, 1.5 mg/kg). HR variability was evaluated by calculating the SDNN (standard deviation of RR intervals) parameter. Results Ro-20-1724 (10 µM) increased beating rate of intact SAN and increased PKA-phosphorylation of key ECC actors (ryanodine receptor, phospholamban and contractile proteins). PDE4 activity was found to account for 60% of total cAMP-PDE activity in SAN. PDE4A, 4B and 4D isoforms were found to be expressed in mouse SAN. In PDE4BKO SAN, the effect of ISO on SAN beating rate was higher than in WT. Ablation of PDE4D induced decreased beating rate in CTRL and ISO conditions and increased Ca2+ spark frequency compared to WT SAN. In vivo, PDE4BKO and PDE4DKO mice displayed increased resting HR during day and night. HR variability was decreased in PDE4BKO, but not in PDE4DKO mice during the day, and decreased in both genotypes at night compared to WT mice. After atropine + propranolol denervation, the rhythmic phenotype was only maintained in PDE4BKO but not in PDE4DKO mice. The response to β-AR stimulation with ISO was higher in PDE4BKO than in PDE4DKO. In addition, under ISO we observed an increased number of premature beats and atrioventricular blocks in PDE4DKO, but not in PDE4BKO mice. Conclusion PDE4B and PDE4D differentially regulate cardiac pacemaker activity. While PDE4B clearly controls intrinsic SAN automaticity, PDE4D might be important for ANS-mediated regulation of HR and conduction.

Intracellular calcium handling heterogeneities in intact guinea pig hearts

2004 ◽  
Vol 286 (2) ◽  
pp. H648-H656 ◽  
Author(s):  
Rodolphe P. Katra ◽  
Etienne Pruvot ◽  
Kenneth R. Laurita
Keyword(s):  
Guinea Pig ◽  
Intracellular Calcium ◽  
Calcium Release ◽  
Optical Mapping ◽  
Contractile Function ◽  
Calcium Transient ◽  
Calcium Transients ◽  
Calcium Handling ◽  
Excitation Light ◽  
Intact Heart

Regional heterogeneities of ventricular repolarizing currents and their role in arrhythmogenesis have received much attention; however, relatively little is known regarding heterogeneities of intracellular calcium handling. Because repolarization properties and contractile function are heterogeneous from base to apex of the intact heart, we hypothesize that calcium handling is also heterogeneous from base to apex. To test this hypothesis, we developed a novel ratiometric optical mapping system capable of measuring calcium fluorescence of indo-1 at two separate wavelengths from 256 sites simultaneously. With the use of intact Langendorff-perfused guinea pig hearts, ratiometric calcium transients were recorded under normal conditions and during administration of known inotropic agents. Ratiometric calcium transients were insensitive to changes in excitation light intensity and fluorescence over time. Under control conditions, calcium transient amplitude near the apex was significantly larger (60%, P < 0.01) compared with the base. In contrast, calcium transient duration was significantly longer (7.5%, P < 0.03) near the base compared with the apex. During isoproterenol (0.05 μM) and verapamil (2.5 μM) administration, ratiometric calcium transients accurately reflected changes in contractile function, and, the direction of base-to-apex heterogeneities remained unchanged compared with control. Ratiometric optical mapping techniques can be used to accurately quantify heterogeneities of calcium handling in the intact heart. Significant heterogeneities of calcium release and sequestration exist from base to apex of the intact heart. These heterogeneities are consistent with base-to-apex heterogeneities of contraction observed in the intact heart and may play a role in arrhythmogenesis under abnormal conditions.

P2558PDE4 regulates cardiac pacemaker function

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
D Mika ◽  
A M Gomez ◽  
R Fischmeister ◽  
G Vandecasteele
Keyword(s):  
Cardiac Pacemaker ◽  
Hydrolytic Activity ◽  
Pde4 Inhibitor ◽  
Pacemaker Activity ◽  
Ventricular Cells ◽  
Pacemaker Function ◽  
S 100 ◽  
Beating Rate ◽  
Respective Contribution

Abstract Background Numerous epidemiological and clinical studies have revealed a positive correlation between heart rate (HR) and cardiovascular morbimortality. The autonomic nervous system is the major extracardiac determinant of HR. During sympathetic stimulation, the activation of β-adrenergic receptors (βAR) induces an increase in cAMP levels, leading to positive chronotropic effect. Among the 5 cardiac cAMP-PDE families, PDE4 is critical for controlling excitation-contraction coupling (ECC) during βAR stimulation in atrial and ventricular cells. PDE4 may also be important for automaticity. 3 genes encode for PDE4s: pde4a, pde4b, pde4d. Their respective contribution to the regulation of pacemaker activity remains ill-defined. Purpose Define the role of PDE4 isoforms in the regulation of cardiac pacemaker activity Methods Total PDE activity was determined in mouse sinoatrial node (SAN) tissue as the cAMP-hydrolytic activity measured in the absence of PDE inhibitor and the fraction corresponding to PDE4 activity was assessed by including the PDE4 inhibitor Ro-20-1724. The in vitro pacemaker activity was assessed by measuring spontaneous Ca2+ transients in Fluo4-loaded-SAN tissue. Images were obtained using confocal microscopy. Results Ro-20-1724 increased beating rate of intact SAN and increased PKA-phosphorylation of key ECC actors (ryanodine receptor, phospholamban and contractile proteins). PDE4 activity was found to account for 60% of the total cAMP-PDE activity in SAN (n=3 independent experiments). PDE4A, PDE4B and PDE4D isoforms were found to be expressed in mouse SAN (n=5 independent experiments). In PDE4D-, but not in PDE4B-deficient mice, Ca2+ homeostasis was altered in control conditions (ctrl) and after βAR stimulation with isoprenaline (iso). Indeed, ablation of PDE4D induced decreased beating rate (ctrl: 1.00±0.08 s–1 vs 1.57±0.05 s–1; iso: 1.71±0.17 s–1 vs 2.39±0.08 s–1, p<0.0001) and increased Ca2+ spark frequency (ctrl: 15.9±5.2 sparks/s/100 μm vs 1.9±0.4 sparks/s/100 μm; iso: 22.9±7.1 sparks/s/100 μm vs 0.6±0.2 sparks/s/100 μm, p<0.0001) (Figure). Calcium Homeostasis in SAN cells Conclusion PDE4 controls pacemaker function in mice and PDE4D ablation strongly perturbs normal SAN activity. Acknowledgement/Funding ANR, Fondation Lefoulon Delalande, CORDDIM

scholarly journals Disease-associated HCN4 V759I variant is not sufficient to impair cardiac pacemaking

2020 ◽  
Vol 472 (12) ◽  
pp. 1733-1742
Author(s):  
Nadine Erlenhardt ◽  
Olaf Kletke ◽  
Franziska Wohlfarth ◽  
Marlene A. Komadowski ◽  
Lukas Clasen ◽  
...  
Keyword(s):  
Family History ◽  
Sick Sinus Syndrome ◽  
Cardiac Pacemaker ◽  
Cell Surface Expression ◽  
Pacemaker Activity ◽  
Hcn Channel ◽  
Functional Interpretation ◽  
Rat Cardiomyocytes ◽  
Cardiac Pacemaking ◽  
History Of

AbstractThe hyperpolarization-activated cation current If is a key determinant for cardiac pacemaker activity. It is conducted by subunits of the hyperpolarization-activated cyclic nucleotide–gated (HCN) channel family, of which HCN4 is predominant in mammalian heart. Both loss-of-function and gain-of-function mutations of the HCN4 gene are associated with sinus node dysfunction in humans; however, their functional impact is not fully understood yet. Here, we sought to characterize a HCN4 V759I variant detected in a patient with a family history of sick sinus syndrome. The genomic analysis yielded a mono-allelic HCN4 V759I variant in a 49-year-old woman presenting with a family history of sick sinus syndrome. This HCN4 variant was previously classified as putatively pathogenic because genetically linked to sudden infant death syndrome and malignant epilepsy. However, detailed electrophysiological and cell biological characterization of HCN4 V759I in Xenopus laevis oocytes and embryonic rat cardiomyocytes, respectively, did not reveal any obvious abnormality. Voltage dependence and kinetics of mutant channel activation, modulation of cAMP-gating by the neuronal HCN channel auxiliary subunit PEX5R, and cell surface expression were indistinguishable from wild-type HCN4. In good agreement, the clinically likewise affected mother of the patient does not exhibit the reported HCN4 variance. HCN4 V759I resembles an innocuous genetic HCN channel variant, which is not sufficient to disturb cardiac pacemaking. Once more, our work emphasizes the importance of careful functional interpretation of genetic findings not only in the context of hereditary cardiac arrhythmias.

scholarly journals The effect of temperature on spontaneous action potential discharge of the isolated sinus venosus from winter and summer plaice (Pleuronectes platessa)

1995 ◽  
Vol 198 (1) ◽  
pp. 137-140 ◽  
Author(s):  
A A Harper ◽  
I P Newton ◽  
P W Watt
Keyword(s):  
Action Potential ◽  
Discharge Rate ◽  
Cardiac Pacemaker ◽  
Intrinsic Rate ◽  
Effect Of Temperature ◽  
Pacemaker Activity ◽  
Duration Of Action ◽  
Diastolic Depolarization ◽  
Significant Difference

The spontaneous cardiac pacemaker activity and conformation were recorded in vitro, using intracellular recording methods, from heart tissue of summer- and winter-caught plaice. The effects of changing temperature on the pacemaker rate, duration of action potential and diastolic depolarization were investigated by altering the temperature of the superfusing medium. The resting intrinsic rate of discharge was significantly greater in pacemaker cells from winter plaice (P=0.05), but there was no significant difference between winter and summer fish in the apparent Arrhenius activation energies for this process. However, there was a significant difference in the estimated intercept, indicating a thermal shift in the processes underlying the spontaneous pacemaker rhythm. There was no significant difference in the diastolic depolarization duration recorded from winter and summer fish over the temperature range 4&shy;22 &deg;C. The major effect of previous environmental temperature was on the duration of the action potential (P&lt;0.02), indicating that the observed changes in pacemaker discharge rate were not influenced by the processes that determine the duration of the pacemaker diastolic depolarisation but were modulated by the channel events that give rise to the action potential.

Cellular and subcellular mechanisms of cardiac pacemaker oscillations

1979 ◽  
Vol 81 (1) ◽  
pp. 205-215
Author(s):  
R. W. Tsien ◽  
R. S. Kass ◽  
R. Weingart
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Surface Membrane ◽  
Cardiac Pacemaker ◽  
Oscillatory Activity ◽  
Purkinje Fibre ◽  
Pacemaker Activity ◽  
Heart Cells ◽  
Control Loop ◽  
Internal Oscillation

Rhythmic oscillations in the membrane potential of heart cells are important in normal cardiac pacemaker activity as well as cardiac arrhythmias. Two fundamentally different mechanisms of oscillatory activity can be distinguished at the cellular and subcellular level. The first mechanism, referred to as a surface membrane oscillator, can be represented by a control loop in which membrane potential changes evoke delayed conductance changes and vice versa. Since the surface membrane potential is a key variable within the control loop, the oscillation can be interrupted at any time by holding the membrane potential constant with a voltage clamp. This mode of oscillation seems to describe spontaneous pacemaker activity in the primary cardiac pacemaker (sinoatrial node) as well as other regions (Purkinje fibre, atrial or ventricular muscle). In all tissues studied so far, the pacemaker depolarization is dominated by the slow shutting-off of an outward current, largely carried by potassium ions. The second mechanism can be called an internal oscillator since it depends upon a subcellular rhythm generator which is largely independent from the surface membrane. Under voltage clamp, the existence of the internal oscillation is revealed by the presence of oscillations in membrane conductance or contractile force which occur even though the membrane potential is held fixed. The two oscillatory mechanisms are not mutually exclusive; the subcellular mechanism can be preferentially enhanced in any given cardiac cell by conditions which elevate intracellular calcium. Such conditions include digitalis intoxication, high Cao, low Nao, low or high Ko, cooling, or rapid stimulation. Several lines of evidence suggest that the subcellular mechanism involves oscillatory variations in myoplasmic calcium, probably due to cycles of Ca uptake and release by the sarcoplasmic reticulum. The detailed nature of the Cai oscillator and its interaction with the surface membrane await further investigation.

Abstract 11423: Mitochondrial Calcium Flux Modulates Pacemaker Activity in Mouse Stem Cell Derived Cardiomyocytes

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
An Xie ◽  
Anyu Zhou ◽  
Hong Liu ◽  
Guangbin Shi ◽  
Kenneth R Boheler ◽  
...  
Keyword(s):  
Ryanodine Receptor ◽  
Mrna Level ◽  
Embryonic Stem ◽  
Calcium Flux ◽  
Pacemaker Activity ◽  
Receptor Subtypes ◽  
Ip3 Receptors ◽  
Cell Current ◽  
Beating Rate

INTRODUCTION: Ca2+ release from sarcoplasmic reticulum (SR) is known to contribute to the pacemaker activity in embryonic stem cells (ESC) derived cardiomyocytes (CMs). Mitochondria are known to participate in Ca2+ cycling. Nevertheless, the role of mitochondria in pacemaker activity is unclear. We studied the role of mitochondrial Ca2+ flux in spontaneously activity of ESC derived CMs. METHODS: CMs were derived from Wt and ryanodine receptor type 2 knockout (RYR2-/-) mouse ESC. Action potentials (APs) were recorded by perforated whole-cell current-clamp. Cytoplasmic and mitochondrial Ca2+ transients were determined by Fluo-4 and Rhod-2 respectively. Mitochondrial Ca2+ uniporter (MCU) siRNA was used. The mRNA level was evaluated by qPCR. RESULTS: As predicted, SR Ca2+ handling inhibitors, 10 μM ryanodine and 2 μM 2-APB, reduced spontaneous beating rate to 56% and 73% respectively in Wt CMs. Inhibition of mitochondrial Ca2+ flux by 10 μM Ru360 showed a similar inhibition effect on the pacemaker activity as 2 μM 2-APB in Wt CMs. To isolate the mitochondrial component, we used RYR2-/- CMs. In these cells, MCU inhibition by pharmacological or molecular biological means reduced beating rate. The MCU mRNA decreased by 96% after MCU siRNA silence 72 hrs (p<0.01). AP and mitochondrial Ca2+ transient synchronous recording revealed that the reduction of spontaneous beating rate accompanied with the depressed mitochondrial Ca2+ uptaking and releasing. In RyR2-/- CMs, 2 μM 2-APB could significantly lower the spontaneous beating rate. While 2 μM 2-APB was applied to MCU silenced RyR2-/- CMs, the beating rate couldn’t be slowed down further. This indicated IP3 receptors reduced spontaneous beating rate via MCU. Thapsigargin could substantially slow down beating rate like 2-APB. Caffeine depletion experiments showed other ryanodine receptor subtypes didn’t contribute Ca2+ release in RyR2-/- CMs. A L-type Ca2+ channel block, 10 μM nifedipine, couldn’t reduce beating frequency. This indicated spontaneous beating rate is Ca2+ influx independent in RyR2-/- CMs. CONCLUSIONS: Mitochondrial Ca2+ handling plays an important role in decreasing spontaneous beating rate. IP3R reduced spontaneous beating rate through MCU.

Sign in / Sign up

Export Citation Format

Share Document