Figure 9.2i Effect of Barium. The red trace shows a Ca²⁺-based AP in normal saline. The blue trace shows an AP from this cell after 15 min in saline with Ba²⁺ substituted for Ca²⁺. Although Ba²⁺ depolarizes the cell by entering through the Ca²⁺ channels, it does not activate the Ca²⁺-activated K⁺ channels involved in repolarization.