The Possibility of Propagation between Myocardial Cells not Connected by Low-Resistance Pathways
The vertebrate myocardium is an assembly of short individual cells, separated at their ends by the intercalated disks (ID). The fluid in the ID gap is continuous with the bulk interstitial fluid, and the gap thickness averages about 200 A (Sperelakis and Rubio, 1971). Regions in which the two membranes come into closer proximity (about 20 A), the gap junctions, are found abundantly in mammalian hearts, but such specialized contacts are rare and much smaller in area in lower vertebrates (for references, see Sperelakis, 1979). A step on the rising phase of the action potential, resembling a post-junctional potential, becomes prominent under conditions of impeded propagation (Hoshiko and Sperelakis, 1962). Increase in gap width occurs in conditions that depress propagation (see Sperelakis, 1979), and the cell-to-cell transmission process is labile (Sperelakis and Hoshiko, 1961; Sperelakis, 1969). Contiguous cells become functionally disconnected at the IDs following focal injury (De Mello, 1972) and under other experimental conditions (see review by Sperelakis, 1979).
KeywordsCardiac Muscle Myocardial Cell Heart Cell External Resistance Intercalate Disk
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