FIG. 17.
Interaction between cell-to-cell coupling and discontinuous propagation. Panel (a): Effect of partial cell-to-cell uncoupling on source-sink mismatch at a site of a tissue discontinuity. Aj: Picture of an engineered culture of neonatal rat ventricular myocytes with a narrow strand (width 50 μm) and transition to a bulk. Ajj: Propagation from the strand into the bulk produces propagation block at the transition. Excited cells (positive membrane potential) are depicted in red, tissue at resting potential level in blue. Propagation from the street to the bulk is blocked, because of source-to-load mismatch. Ajjj: Partial uncoupling with palmitoleic acid restores propagation. Ajv: Total uncoupling produces propagation block. Reproduced with permission from S. Rohr et al., Science 275, 5301 (1997). Copyright 1997 American Association for the Advancement of Science.89 Panel (b): Sketch explaining the biophysical mechanism: The simplified electrical equivalent circuit shows excitable elements (cells) in green, intercellular resistors representing gap junctions in the x-direction in black, and intercellular resistors representing gap junctions in the y-direction in red. Panel (c): Numerical presentation of the dependence of the critical strand width hc, producing propagation block, on cell-to-cell coupling (expressed as intercellular resistance). Hatched area corresponds to propagation block. An increase in coupling resistance, Ry, facilitates propagation, whereas changing Rx has no effect on block formation. This phenomenon is explained by the fact that the only an increase in Ry- resistors reduce the dispersion of current at the geometrical transition. Reproduced with permission from V. G. Fast et al., Cardiovasc. Res. 30, 3 (1995). Copyright 1995 Oxford University Press.79