FIG. 9.

Electrical propagation at the cellular level. Panels (a)–(c): Propagation in a chain of a single cells [neonatal rat ventricular myocytes, panel (a) with dark dots showing locations of three light-sensitive diodes (6 μm in width)]. Two diodes are projected on the cytoplasm of a single cell; the third diode is placed in the adjacent cell, separated from the other diodes by a single cell junction. Panel (b) shows the change in fluorescence of a voltage-sensitive dye representing the action potential upstrokes. Panel (c): Cytoplasmic and cell-to-cell conduction times illustrating that a single cell-to-cell junction introduces a propagation delay of about 60 μs. Panels (d)–(f): Propagation in an anisotropic cellular network [panel (d)] with dark dots showing locations of light-sensitive diodes (6 μm in width). Panel (e): Fluorescence changes illustrating action potential upstrokes from the three diodes. Panel (f): In contrast to panel (c), there are no detectable propagation delays introduced by cell-to-cell junctions. Comparison of panels (c) and (f) indicates that lateral apposition of cells cancels delays produced by single cell-to-cell junctions (so-called “lateral averaging”). Reproduced with permission from V. G. Fast et al., Cir. Res. 73, 5 (1993). Copyright 1993 Wolters Kluwer Health, Inc.⁶⁷