. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 10 s Figure 9. Effects on myocardial activity of injecting DC current. The recording electrode was inserted near the anterior end of the heart, and the current electrode near the posterior end. In each record, intracel- lular activity of the heart muscle (upper trace) and monitor of the current applied (lower trace) are shown. Depolarizing ( + ) or hyperpolarizing (-) DC current was applied for 10 s. Intensity of the current (nA) was + 10 (A), +20 (B), +30 (C), -40 (D), -50 (E). and -60 (F). cardiac ganglion (Anderson and Co
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 10 s Figure 9. Effects on myocardial activity of injecting DC current. The recording electrode was inserted near the anterior end of the heart, and the current electrode near the posterior end. In each record, intracel- lular activity of the heart muscle (upper trace) and monitor of the current applied (lower trace) are shown. Depolarizing ( + ) or hyperpolarizing (-) DC current was applied for 10 s. Intensity of the current (nA) was + 10 (A), +20 (B), +30 (C), -40 (D), -50 (E). and -60 (F). cardiac ganglion (Anderson and Cooke, 1971). In the myogenic heart of embryos and early juveniles of the isopod Ligia, the muscle activity is not affected by appli- cation of TTX, except for the TTX-sensitive spike on the slow potential (Yamagishi, 1996; Yamagishi and Hirose, 1997). The ineffectiveness of TTX on the Triops heart supports the idea that the rhythmicity of this myocardium is generated endogenously. The electrical activity of the Triops heart consists of only slow potentials, and the amplitude of the slow poten- tial changes gradually during measurement. But no spike potentials ever appeared, even after termination of a hy- perpolarizing DC current injected into the heart muscle ( Fig. 8). The heart muscle of Triops, generating membrane potential oscillation, may lack the ability to generate all-or-none membrane potentials. Characteristics of the heart as a single muscle oscillator No localized regions of the Triops heart consistently generated potentials that preceded those of other regions (Fig. 3A). Moreover, any cut fragment of the heart exhib- ited spontaneous muscle activity (Fig. 3B). These results suggest that the heart of Triops has diffuse myogenicity, and that individual muscle cells are inherently oscillatory. When the central region of the heart was arrested by a mechanical stimulus, the anterior and posterior regions vital staining with methylene blue or by microscopic ob- serva
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
