Figure 9.1i Reduced Calcium. The red trace shows a Ca²⁺-based AP in normal saline. The blue trace shows an AP from this cell after 15 min in low Ca²⁺ saline. AP amplitude decreases due to the decreased Nernst potential for Ca²⁺. The AP is broader because less Ca²⁺ enters the cell to activate Ca²⁺-activated K⁺ channels involved in repolarization.