Intracellular stimulation and recording from single cardiac cells in the rabbit atrium

• Published in: Journal of electrocardiology Vol. 7; no. 2; pp. 119 - 126
• Main Authors: Ushiyama, Junji, Brooks, Chandler McC
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 1974
• Subjects: Animals; Atrial Function; Differential Threshold; Electric Stimulation; Electrophysiology; Heart Atria - cytology; Heart Conduction System - cytology; Heart Conduction System - physiology; Microelectrodes; Rabbits
• ISSN: 0022-0736; 1532-8430
• DOI: 10.1016/S0022-0736(74)80021-X

The mechanism of pacemaker action in an isolated rabbit sinoatrial node preparation was studied by means of intracellular stimulation and recording through a single-barrelled microelectrode. This technique permitted not only stimulation of individual cells of the various types found in and around the pacemaker tissue but also the recording of nonpropagated activity in cells stimulated or in those in the immediate vicinity. It was found that: 1) The myocardial atrial fiber has a threshold of the order of 10 −6 A. when stimulated intracellulary with a 15 msec duration pulse. This threshold was constant throughout diastole, except during its very early phase. The resulting response was of an all-or-none type and propagated over the tissue. 2) Thresholds for latent pacemaker cells were different from cell to cell; within a cell, it also varied slightly with the degree of diastolic depolarization attained. The response initiated by intracellular stimulation was also of an all-or-none type and, in most cases, it was propagated to the atrium. When a response was induced at an early phase in diastole, a conduction failure was sometimes observed. When such a nonpropagated response occurred in a latent pacemaker cell, the duration of diastole was increased. 3) Most pacemaker cells tested did not respond to intracellular stimulation. In a few cells, however, a graded response proportional to stimulus intensity, was obtained. Such response did not propagate to the atrium. These graded responses differed from the local responses which occur in other types of cell. It was concluded that a synchronization of pacemaker cell activity is required for effective pacemaker action.