Sharp Repolarization of Stimulated Cell (A5). Sharp repolarization of only the last cell (5th) of the 5-cell chain when a repolarizing IS2 pulse was applied in cardiac muscle (A-B) and in smooth muscle (C-D). Panels A and C illustrate the records obtained when the applied IS2 pulse was just not quite strong enough to produce a permanent repolarization of cell #5. In panels B and D, the IS2 intensity was slightly increased to produce an all-or-none repolarization. The membrane potential of adjacent cell #4 (A4) was only slightly changed when cell A5 underwent a very large change. The velocity of antegrade propagation (θa) was about 54 cm/sec in CM and 8.9 cm/sec in SM under that conditions.