Figure 6.

Role of gap junctions in propagating of the cardiac action potential. (A) The cardiac tissue is eletrically homogenous if the adjacent cells are coupled by gap junction channels. The anisotropic nature of gap junction channel distribution favors longitudinal over transversal conduction. (B) Conditions that decrease or abolish coupling between the cells may cause a unidirectional conduction block and as the electrical impulse propagates around the block it can re-excite those tissue regions due to differences in refractoriness. Insert shows cell-cell connections via gap junction channels. The main causes of uncoupling of the cells (showed in red) are elevated intracellular Ca²⁺ concentration, reduction in H⁺ concentration, or lower levels of ATP. Cx, connexon; ATP, adenosine triphosphate.