Electrical Events in Specialized Muscle Fibers of a Mammalian Right Atrium

Miyauchi, Atsuyoshi

doi:10.1536/ihj.3.357

Cited by 8 publications

(2 citation statements)

References 2 publications

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“…A 388 HOGAN, DAVIS number of investigators have described several different configurations of action potentials (12)(13)(14)(15)(16)(17)(18). Paes de Carvalho et al (12), for example, found that the rabbit atrium contains several distinct types of fibers.…”

Section: Ciratlm'on Esearch Vol XXIII September 1968mentioning

confidence: 99%

Evidence for Specialized Fibers in the Canine Right Atrium

Hogan

Davis

1968

Circulation Research

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Right atria from excised beating dog hearts were immersed in Tyrode solution with the endocardial surface of the anterior wall exposed. Glass microelectrodes were used to impale fibers in different anatomical areas of this preparation. Fibers with action potentials similar in contour to those of ventricular Purkinje fibers were found along the caval border of the crista terminalis in the area of the posterior internodal tract. The action potential of these fibers (plateau fibers) had a resting potential of -85 to -95 mv, a sharp spiked overshoot, a long plateau phase, and inherent diastolic depolarization. The maximum velocity of the action potential upstroke of plateau fibers was consistently greater than that of simultaneously recorded fibers which lacked a plateau phase (regular fibers). Epinephrine or isoproterenol produced an increase in both rate and magnitude of diastolic depolarization of plateau fibers and on occasion converted them to true pacemakers. Acetylcholine accelerated repolarization of plateau fibers with disappearance of the plateau. Increases in extracellular concentration of potassium ions from 2.7 to 10.8 mM rendered regular atrial fibers inexcitable, but plateau fibers continued to show action potentials. Plateau atrial fibers possess several characteristics exhibited by specialized conducting and impulse generating fibers. The possibility that these fibers constitute the posterior internodal tract and function in preferential conduction of excitation to the A-V node was discussed. ADDITIONAL KEY WORDShigh extracellular potassium concentration posterior internodal tract epinephrine diastolic depolarization acetylcholine latent pacemaker activity isoproterenol• While it is generally accepted that fibers of the sJnoatrial (S-A) node serve as the pacemakers in the normal mammalian heart, the manner in which excitation spreads from this node through the atria and to the atrioventricular (A-V) node is not completely settled. Lewis et al. (1) concluded from studies using surface electrodes that excitation spreads radially from the S-A node through a syncytium composed of homogeneous tissue. The concept of radial spread of the impulse was challenged by Eyster and Meek (2-5) who presented evidence for spread of excitation from the S-A node to the From the Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706.This investigation was supported in part by grants from the Wisconsin Heart Association and U. S. Public Health Service Grants 5-T1-HE53705-08 and 2-T1-HE5540-06.Accepted for publication June 27, 1968.CiratlM 'on esearch, Vol. XXIII, September 1968 A-V node along a preferential pathway. Also evidence for rapid spread of the impulse from the right to the left atrium was given by Bachmann (6) who described a special bundle of tissue linking the atria ventrally. Both anatomical and electrophysiological evidence has accumulated to support the contentions of Eyster and Meek for a preferential internodal pathway. In a recent review, Robb and Petri (7...

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Section: Ciratlm'on Esearch Vol XXIII September 1968mentioning

confidence: 99%

Evidence for Specialized Fibers in the Canine Right Atrium

Hogan

Davis

1968

Circulation Research

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“…Thus, Hoffman and Cranefield 1 and Paes de Carvalho-have described propagation from the sinus node to the atrioventricular node, but these reports include little information about passage of excitation from the sinus node to surrounding atrial muscle. One group of investigators including Horibe 8 and Miyauchi 4 has studied this problem in detail. Nevertheless, many important features of excitation in this region are not well known and this study was done to provide additional information on this problem.…”

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confidence: 99%

Spread of Excitation from the Sinus Node

Sano

Yamagishi

1965

Circulation Research

167

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Microelectrodes were employed to determine the mode of propagation of excitation from the sinus node in the rabbit heart. The excitation starts from the sinus node radially, at first, but then proceeds to the crista terminalis, often obliquely. This is because some special tissue having a slow conduction velocity lies behind the sinus node, and also because there is a zone of relatively faster conduction at the basal wall of the superior vena cava. Once the excitation wave enters the crista terminalis, it travels rapidly in two opposite directions through two branches of the ring-like structure which is formed by the crista terminalis and its extension. The excitation wave traveling through the branch encircling the inferior vena cava reached the atrioventricular node earlier in most instances. In the caval region inside the ring-like structure there is a zone of relatively faster conduction. The conduction to the atrioventricular node through this route is latent in the normal state, because conduction through the ring-like structure takes place beforehand. In the caval region near the sinus node, the conduction velocity of the excitation wave from the spontaneously beating sinus node was greater than that from the electrically driven atrium. The spontaneous action potential showed also a steeper rise than that produced by electrical stimulation. The mechanism responsible for this is discussed.

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Are there internodal tracts? Yes

Liebman

1985

International Journal of Cardiology

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Electrical Events in Specialized Muscle Fibers of a Mammalian Right Atrium

Cited by 8 publications

References 2 publications

Evidence for Specialized Fibers in the Canine Right Atrium

Evidence for Specialized Fibers in the Canine Right Atrium

Spread of Excitation from the Sinus Node

Are there internodal tracts? Yes

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