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To correlate changes in pacemaker frequency with those of length and tension in mammalian atrial tissues, a strip of the sinoatrial (SA) nodal tissue (about 10 mm in length and 4 mm in width) isolated from the rabbit heart was subjected to constant-length and constantload stretches, and the relation between the resulting pacemaker frequency changes and the segmental length changes of the preparation was examined by means of cinematographic recording of the preparation with carbon markers on its surface. The amount of stretch-induced length changes was larger in the perinodal tissue segments than in the SA nodal segments, indicating that the nodal area is less extensible than the perinodal area. The time course of stretch-induced length changes of one nodal segment (closer to the inferior versa cava) was found to roughly parallel that of pacemaker frequency changes, suggesting that the pacemaker frequency is primarily dependent on the length but not on the tension of the SA nodal area.

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KAMIYAMA, A., and INOUE, F. 1971. Conduction delay from Purkinje fiber to ventricular muscle studied with extracellular microelectrodes. Can. J. Physiol. Pharmacol. 49, 678-684.The relationship between electrical activity recorded intracellularly and extracellularly was studied in canine right ventricle. When the tip of a microelectrode was placed against a Purkinje fiber the electrical activity obtained had two components. The first component was a sharp diphasic wave which was defined as an action current while the second component was a rounded and flat diphasic wave which was defined as a field potential. Transmembrane action potentials recorded at the same site indicated that the first component was an active membrane current of the Purkinje fiber while the second component was identified as the field effect potential generated by ventricular fibers lying directly under the layer of Purkinje fibers. In areas where the Purkinje fibers were absent only the second component was present. The time delay of approximately 5 ms between the two components represents the conduction delay of the impulse from the Purkinje fiber to the ventricular fiber. KAMIYAMA,A,, et INOUE, F. 1971. Conduction delay from Purkinje fiber to ventricular muscle studied with extracellular microelectrodes. Can. I. Physiol. Pharmacol. 49, 678-684. Sur des fragments de tissus ventriculaire droit, nous avons ttudit les relations entre I'activitC tlectrique intra et extracellulaire. Lorsque la pointe de la microtlectrode est positionnte au dessus d'une cellule de Purkinje, I'activitk tlectrique enregistrte prtsente deux composantes. La premihre, dCfinie comme un courant d'action, est constitute d'une onde rapide et diphasique.La seconde consiste en une onde diphasique lente et rtsulte d'un champ de potentiel. Par comparaison avec I'activitt Clectrique intracellulaire, il apparai"t que la premihre composante rtsulte d'un courant membranaire des cellules de Purkinje tandis que la second risulte d'un champ de potentiel crtC par les fibres ventriculaires sous-jacentes. Au niveau des regions dtpourvues de cellules de Purkinje, seule la seconde composante est enregistrte. La latence entre les deux composantes est de l'ordre de 5m sec reprtsentant le temps de conduction de I'influx entre les cellules de Purkinje et les cellules ventriculaires.

No abstract