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Hucker WJ, Ripplinger CM, Fleming CP, Fedorov VV, Rollins AM, Efimov IR. Bimodal biophotonic imaging of the structure-function relationship in cardiac tissue. JOURNAL OF BIOMEDICAL OPTICS 2008; 13:054012. [PMID: 19021392 PMCID: PMC2719892 DOI: 10.1117/1.2975826] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The development of systems physiology is hampered by the limited ability to relate tissue structure and function in intact organs in vivo or in vitro. Here, we show the application of a bimodal biophotonic imaging approach that employs optical coherence tomography and fluorescent imaging to investigate the structure-function relationship at the tissue level in the heart. Reconstruction of cardiac excitation and structure was limited by the depth penetration of bimodal imaging to approximately 2 mm in atrial tissue, and approximately 1 mm in ventricular myocardium. The subcellular resolution of optical coherence tomography clearly demonstrated that microscopic fiber orientation governs the pattern of wave propagation in functionally characterized rabbit sinoatrial and atrioventricular nodal preparations and revealed structural heterogeneities contributing to ventricular arrhythmias. The combination of this bimodal biophotonic imaging approach with histology and/or immunohistochemistry can span multiple scales of resolution for the investigation of the molecular and structural determinants of intact tissue physiology.
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Affiliation(s)
- William J Hucker
- Washington University, Department of Biomedical Engineering, St. Louis, Missouri 63130, USA
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Fedorov VV, Glukhov AV, Sudharshan S, Egorov Y, Rosenshtraukh LV, Efimov IR. Electrophysiological mechanisms of antiarrhythmic protection during hypothermia in winter hibernating versus nonhibernating mammals. Heart Rhythm 2008; 5:1587-96. [PMID: 18984537 DOI: 10.1016/j.hrthm.2008.08.030] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2008] [Accepted: 08/26/2008] [Indexed: 11/15/2022]
Abstract
BACKGROUND Robust cell-to-cell coupling is critically important in the safety of cardiac conduction and protection against ventricular fibrillation (VF). Hibernating mammals have evolved naturally protective mechanisms against VF induced by hypothermia and reperfusion injury. OBJECTIVE We hypothesized that this protection strategy involves a dynamic maintenance of conduction and repolarization patterns through the improvement of gap junction functions. METHODS We optically mapped the hearts of summer-active (SA) and winter-hibernating (WH) ground squirrels Spermophilus undulatus from Siberia and nonhibernating rabbits during different temperatures (+3 degrees C to +37 degrees C). RESULTS Midhypothermia (+17 degrees C) resulted in nonuniform conduction slowing, increased dispersion of repolarization, shortened wavelength, and consequently enhanced VF induction in SA ground squirrels and rabbits. In contrast, wavelength was increased during hypothermia in WH hearts in which VF was not inducible at any temperature. In SA and rabbit hearts, but not in WH, conduction anisotropy was significantly increased by pacing acceleration, thus promoting VF induction during hypothermia. WH hearts maintained the same rate-independent anisotropic propagation pattern even at 3 degrees C. connexin 43 (Cx43) had more homogenous transmural distribution in WH ventricles as compared to SA. Moreover, Cx43 and N-cadherins (N-cad) densities as well as the percentage of their colocalization were significantly higher in WH compared to SA epicardium. CONCLUSION Rate-independent conduction anisotropy ratio, low dispersion of repolarization, and long wavelength-these are the main electrophysiological mechanisms of antiarrhythmic protection in hibernating mammalian species during hypothermia. This strategy includes the improved gap junction function, which is due to overexpression and enhanced colocalization of Cx43 and N-cad.
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Affiliation(s)
- Vadim V Fedorov
- Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130-4899, USA.
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Abramochkin DV, Suris MA, Sukhova GS, Rozenshtraukh LV. Acetylcholine-induced suppression of electric activity of working myocardium of the cod atrium. DOKLADY BIOLOGICAL SCIENCES : PROCEEDINGS OF THE ACADEMY OF SCIENCES OF THE USSR, BIOLOGICAL SCIENCES SECTIONS 2008; 419:73-6. [PMID: 18536265 DOI: 10.1134/s0012496608020014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- D V Abramochkin
- Moscow State University, Leninskie gory, Moscow, 117234, Russia
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Efimov IR, Hucker WJ. To the Editor—Response. Heart Rhythm 2008. [DOI: 10.1016/j.hrthm.2007.12.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Atria are more susceptible to electroporation than ventricles: implications for atrial stunning, shock-induced arrhythmia and defibrillation failure. Heart Rhythm 2008; 5:593-604. [PMID: 18362029 DOI: 10.1016/j.hrthm.2008.01.026] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/27/2007] [Accepted: 01/17/2008] [Indexed: 11/21/2022]
Abstract
BACKGROUND Defibrillation shock is known to induce atrial stunning, which is electrical and mechanical dysfunction. OBJECTIVE We hypothesized that atrial stunning is caused by higher atrial susceptibility to electroporation vs ventricles. We also hypothesize that electroporation may be responsible for early recurrence of atrial fibrillation. METHODS We investigated electroporation induced by 10-ms epicardial high-intensity shocks applied locally in atria and ventricles of Langendorff-perfused rabbit hearts (n = 12) using optical mapping. RESULTS Electroporation was centered at the electrode and was evident from transient diastolic depolarization and reduction of action potential amplitude and maximum upstroke derivative. Electroporation was voltage-dependent and polarity-dependent and was significantly more pronounced in the atria vs ventricles (P <.01), with a summary 50% of Effective Dose (ED50) for main measured parameters of 9.2 +/- 3.6 V/cm and 13.6 +/- 3.2 V/cm in the atria vs 37.4 +/- 1.5 V/cm and 48.4 +/- 2.8 V/cm in the ventricles, for anodal and cathodal stimuli, respectively. In atria (n = 5), shocks of both polarities (27.2 +/- 1.1 V/cm) transiently induced conduction block and reentry around the inexcitable area. Electroporation-induced ectopic activity was a possible trigger for reentry. However, in the thicker ventricles, electroporation and resulting conduction slowing and block were restricted to the surface only, preventing complete block and arrhythmia. The upstroke morphology revealed that the wave front dived below the electroporated region and resurfaced into unaffected epicardial tissue. CONCLUSION We showed that the atria are more vulnerable to electroporation and resulting block and arrhythmia than the ventricles.
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Ripplinger CM, Li W, Hadley J, Chen J, Rothenberg F, Lombardi R, Wickline SA, Marian AJ, Efimov IR. Enhanced transmural fiber rotation and connexin 43 heterogeneity are associated with an increased upper limit of vulnerability in a transgenic rabbit model of human hypertrophic cardiomyopathy. Circ Res 2007; 101:1049-57. [PMID: 17885214 PMCID: PMC2366809 DOI: 10.1161/circresaha.107.161240] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Human hypertrophic cardiomyopathy, characterized by cardiac hypertrophy and myocyte disarray, is the most common cause of sudden cardiac death in the young. Hypertrophic cardiomyopathy is often caused by mutations in sarcomeric genes. We sought to determine arrhythmia propensity and underlying mechanisms contributing to arrhythmia in a transgenic (TG) rabbit model (beta-myosin heavy chain-Q403) of human hypertrophic cardiomyopathy. Langendorff-perfused hearts from TG (n=6) and wild-type (WT) rabbits (n=6) were optically mapped. The upper and lower limits of vulnerability, action potential duration (APD) restitution, and conduction velocity were measured. The transmural fiber angle shift was determined using diffusion tensor MRI. The transmural distribution of connexin 43 was quantified with immunohistochemistry. The upper limit of vulnerability was significantly increased in TG versus WT hearts (13.3+/-2.1 versus 7.4+/-2.3 V/cm; P=3.2e(-5)), whereas the lower limits of vulnerability were similar. APD restitution, conduction velocities, and anisotropy were also similar. Left ventricular transmural fiber rotation was significantly higher in TG versus WT hearts (95.6+/-10.9 degrees versus 79.2+/-7.8 degrees; P=0.039). The connexin 43 density was significantly increased in the mid-myocardium of TG hearts compared with WT (5.46+/-2.44% versus 2.68+/-0.77%; P=0.024), and similar densities were observed in the endo- and epicardium. Because a nearly 2-fold increase in upper limit of vulnerability was observed in the TG hearts without significant changes in APD restitution, conduction velocity, or the anisotropy ratio, we conclude that structural remodeling may underlie the elevated upper limit of vulnerability in human hypertrophic cardiomyopathy.
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MESH Headings
- Action Potentials/physiology
- Animals
- Animals, Genetically Modified
- Arrhythmias, Cardiac/diagnostic imaging
- Arrhythmias, Cardiac/pathology
- Arrhythmias, Cardiac/physiopathology
- Cardiomyopathy, Hypertrophic/diagnostic imaging
- Cardiomyopathy, Hypertrophic/pathology
- Cardiomyopathy, Hypertrophic/physiopathology
- Connexin 43/genetics
- Connexin 43/metabolism
- Diffusion Magnetic Resonance Imaging
- Disease Models, Animal
- Echocardiography
- Female
- Genetic Heterogeneity
- Immunohistochemistry
- Male
- Myocardial Contraction/physiology
- Myocardium/metabolism
- Myocytes, Cardiac/pathology
- Myocytes, Cardiac/physiology
- Rabbits
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Affiliation(s)
- Crystal M Ripplinger
- Department of Biomedical Engineering, Washington University, St Louis, MO 63130, USA
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Baruscotti M, Robinson RB. Electrophysiology and pacemaker function of the developing sinoatrial node. Am J Physiol Heart Circ Physiol 2007; 293:H2613-23. [PMID: 17827259 DOI: 10.1152/ajpheart.00750.2007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The sinoatrial node performs its task as a cardiac impulse generator throughout the life of the organism, but this important function is not a constant. Rather, there are significant developmental changes in the expression and function of ion channels and other cellular elements, which lead to a postnatal slowing of heart rate and may be crucial to the reliable functioning of the node during maturation. In this review, we provide an overview of current knowledge regarding these changes, with the main focus placed on maturation of the ion channel expression profile. Studies on Na(+) and pacemaker currents have shown that their contribution to automaticity is greater in the newborn than in the adult, but this age-dependent decrease is at least partially opposed by an increased contribution of L-type Ca(2+) current. Whereas information regarding age-dependent changes in other transmembrane currents within the sinoatrial node are lacking, there are data on other relevant parameters. These include an increase in the nodal content of fibroblasts and in the area of nonexpression of connexin43, considered a molecular marker of nodal tissue. Although much remains to be done before a comprehensive view of the developmental biology of the node is available, important evidence in support of a molecular interpretation of developmental slowing of the intrinsic sinoatrial rate is beginning to emerge.
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Affiliation(s)
- Mirko Baruscotti
- Laboratory of Molecular Physiology and Neurobiology, Department of Biomolecular Sciences and Biotechnology, University of Milano, Milan, Italy
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Bolter CP, English DJ. The effects of tertiapin-Q on responses of the sinoatrial pacemaker of the guinea-pig heart to vagal nerve stimulation and muscarinic agonists. Exp Physiol 2007; 93:53-63. [PMID: 17720744 DOI: 10.1113/expphysiol.2007.038901] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Using Langendorff preparations of the guinea-pig heart, we have examined the participation of the acetylcholine (ACh)-activated potassium channel, IK,ACh, in the bradycardia produced by electrical stimulation of the vagus (parasympathetic) nerve and muscarinic agonists (ACh and bethanecol, bolus i.a.). Hearts from young animals (160-250 g) were perfused with Krebs-Henseleit solution, and pacemaker frequency was determined from the P wave of an ECG. Tertiapin-Q was used to block IK,ACh. Vagal stimulation (10 s trains at 2, 5 and 10 Hz) produced graded reductions in atrial rate that were substantially attenuated, and to a similar extent, by 300 nm and 1 microm tertiapin-Q (to 0.42 +/- 0.12, mean +/- s.d., of the control values; P < 0.001). Acetylcholine (3 nmol) produced brief graded bradycardias that were also attenuated by tertiapin-Q (0.24 +/- 0.24; P = 0.006). Similar results were obtained when experiments were repeated in 2 mm Cs+ (to block the hyperpolarization-activated pacemaker current). Bethanecol (30, 50 and 70 nmol), a muscarinic agonist with no appreciable nicotinic activity, produced sustained bradycardias that were attenuated by 300 nm tertiapin-Q (0.36 +/- 0.21; P < 0.0001). The responses to vagal stimulation and ACh developed more slowly in tertiapin-Q, indicating that a rapidly acting mechanism had been blocked. Responses to vagal stimulation were faster in 2 mm Cs+. Together, these observations show that ACh released from parasympathetic nerve varicosities exerts a considerable part of its effect on the pacemaker by activating IK,ACh and acts in a manner not readily distinguishable from that of directly applied muscarinic agonists.
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Affiliation(s)
- Chris P Bolter
- Department of Physiology, School of Medical Sciences, University of Otago, PO Box 913, Dunedin 9054, New Zealand.
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Hucker WJ, Nikolski VP, Efimov IR. Autonomic control and innervation of the atrioventricular junctional pacemaker. Heart Rhythm 2007; 4:1326-35. [PMID: 17905339 DOI: 10.1016/j.hrthm.2007.06.011] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Accepted: 06/07/2007] [Indexed: 11/21/2022]
Abstract
BACKGROUND The main physiologic function of the AV junction is control of timing between atrial and ventricular excitation. However, under pathologic conditions, the AV junction may become the pacemaker of the heart. Unlike the well-characterized sinoatrial node (SAN), autonomic control of the AV junctional pacemaker has not been studied. OBJECTIVE The purpose of this study was to characterize the autonomic control and innervation of the AV junctional pacemaker. METHODS The response of rabbit AV junctional pacemaker to autonomic stimulation was investigated using optical mapping, autonomic modulation via subthreshold stimulation (n = 12), and quantitative immunohistochemistry (n = 5), and the density of parasympathetic and sympathetic innervation in optically mapped preparations was quantified. RESULTS Subthreshold stimulation applied adjacent to the conduction system in the triangle of Koch autonomically modulates the junctional rate, and parasympathetic and sympathetic components can be separated with atropine and the beta-blocker nadolol. Subthreshold stimulation increased the rate maximally to 2.1 +/- 0.4 times when applied with atropine. Unlike the SAN pacemaker, which shifts significantly in response to autonomic stimulation, the AV junctional pacemaker remains stationary (most often in the inferior nodal extension), moving in only 5% of subthreshold stimulation trials. Staining with tyrosine hydroxylase and choline acetyltransferase revealed heterogeneous innervation within the AV junction. CONCLUSION AV junctional rhythm can be autonomically modulated with subthreshold stimulation to produce junctional rates of 145 +/- 16 bpm (cycle length 412 +/- 29 ms), similar to sinus rates in rabbit. Unlike the SAN, the anatomic location of the AV junctional pacemaker is stable during autonomic modulation.
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Affiliation(s)
- William J Hucker
- Department of Biomedical Engineering, Washington University, One Brookings Drive, St. Louis, MO 63130, USA
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Hucker WJ, Sharma V, Nikolski VP, Efimov IR. Atrioventricular conduction with and without AV nodal delay: two pathways to the bundle of His in the rabbit heart. Am J Physiol Heart Circ Physiol 2007; 293:H1122-30. [PMID: 17496219 DOI: 10.1152/ajpheart.00115.2007] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The electrophysiological properties of atrioventricular (AV) nodal dual pathways have traditionally been investigated with premature stimuli delivered with right atrial pacing. However, little is known about the functional characteristics of AV nodal inputs outside of this context. Superfused rabbit triangle of Koch preparations (n = 8) and Langendorff-perfused hearts (n = 10) were paced throughout the triangle of Koch and mapped electrically and optically for activation pattern, electrogram and optical action potential morphologies, stimulation thresholds, and stimulus-His (S-H) intervals. Optical mapping and changes in His electrogram morphology were used to confirm the activation pathway. Pacing stimuli >or=2 mm above the tricuspid valve caused fast-pathway activation of the AV node and His with a threshold of 2.4 +/- 1.6 mA. An area directly below the coronary sinus had high thresholds (8.6 +/- 1.4 mA) that also resulted in fast-pathway excitation (P < 0.001). S-H intervals (81 +/- 19 ms) for fast-pathway activation remained constant throughout the triangle of Koch, reflecting the AV delay. Stimuli applied <2 mm from the tricuspid valve resulted in slow pathway (SP) excitation or direct His excitation (4.4 +/- 2.2 mA threshold; P < 0.001 compared with fast pathway). For SP/His pacing, S-H intervals showed a strong dependence on the distance from the His electrode and were significantly lower than S-H intervals for fast-pathway activation. SP/His pacing also displayed characteristic changes in His electrogram morphology. In conclusion, optical maps and S-H intervals for SP/His activation suggest that AV conduction via SP bypasses the compact AV node via the lower nodal bundle, which may be utilized to achieve long-term ventricular synchronization.
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Affiliation(s)
- William J Hucker
- Biomedical Engineering Department, Washington University, 1 Brookings Drive, St. Louis, MO 63130, USA
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Fedorov VV, Lozinsky IT, Sosunov EA, Anyukhovsky EP, Rosen MR, Balke CW, Efimov IR. Application of blebbistatin as an excitation-contraction uncoupler for electrophysiologic study of rat and rabbit hearts. Heart Rhythm 2007; 4:619-26. [PMID: 17467631 DOI: 10.1016/j.hrthm.2006.12.047] [Citation(s) in RCA: 281] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2006] [Accepted: 12/27/2006] [Indexed: 11/27/2022]
Abstract
BACKGROUND Application of fluorescence imaging of cardiac electrical activity is limited by motion artifacts and/or side effects of currently available pharmacologic excitation-contraction uncoupling agents. OBJECTIVES The purpose of this study was to test whether blebbistatin, a recently discovered inhibitor of myosin II isoforms, can be used as an excitation-contraction uncoupler. METHODS The specificity and potency of blebbistatin were examined by assaying the effects of blebbistatin on the contraction and basic cardiac electrophysiologic parameters of Langendorff-perfused rabbit hearts, isolated rabbit right ventricle and right atrium, and single rat ventricular myocytes using conventional ECG, surface electrograms, microelectrode recordings, and optical imaging with voltage-sensitive and Ca(2+)-sensitive dyes. Action potential morphology, ECG parameters, cardiac conduction, and refractoriness were determined after perfusion with 0.1-10 microM blebbistatin. RESULTS Blebbistatin 5-10 microM completely eliminated contraction in all cardiac preparations but did not have any effect on electrical activity, including ECG parameters, atrial and ventricular effective refractory periods, and atrial and ventricular activation patterns. Blebbistatin 10 microM had no effects on action potential morphology in rabbit cardiac tissue. Blebbistatin inhibited single cellular contraction in a dose-dependent manner with half-maximal inhibitory concentration (IC(50)) = 0.43 microM, without altering the morphologies of intracellular calcium transients. The blebbistatin effect was completely reversible by simultaneous washout and photobleaching by ultraviolet light CONCLUSION Blebbistatin is a promising novel selective excitation-contraction uncoupler that can be used for optical imaging of cardiac tissues.
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Affiliation(s)
- Vadim V Fedorov
- Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130-4899, USA
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Opthof T. Embryological development of pacemaker hierarchy and membrane currents related to the function of the adult sinus node: implications for autonomic modulation of biopacemakers. Med Biol Eng Comput 2007; 45:119-32. [PMID: 17203321 DOI: 10.1007/s11517-006-0138-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2006] [Accepted: 11/22/2006] [Indexed: 10/23/2022]
Abstract
The sinus node is an inhomogeneous structure. In the embryonic heart all myocytes have sinus node type pacemaker channels (I (f)) in their sarcolemma. Shortly before birth, these channels disappear from the ventricular myocytes. The response of the adult sinus node to changes in the interstitium, in particular to (neuro)transmitters, results from the interplay between the responses of all of its constituent cells. The response of the whole sinus node cannot be simply deduced from these cellular responses, because all cells have different responses to specific agonists. A biological pacemaker will be more homogeneous. Therefore it can be anticipated that tuning of cycle length may be problematic. It is discussed that efforts to create a biological pacemaker responsive to vagal stimulation, may be counterproductive, because it may have the potential risk of 'standstill' of the biological pacemaker. A normal sinus node remains spontaneously active at high concentrations of acetylcholine, because it has areas that are unresponsive to acetylcholine. The same is pertinent to other substances with a negative chronotropic effect. Such functional inhomogeneity is lacking in biological pacemakers.
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Affiliation(s)
- Tobias Opthof
- Experimental and Molecular Cardiology Group, Academic Medical Center, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.
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