FIGURE 3.

Effects of inward current blockade on APs measured with constant and I_K1 current injection. (A) Typical APs of one atrial myocyte in absence (baseline) and presence of lidocaine to block the fast Na⁺ current. Inset: first derivatives of the AP upstrokes, reflecting the amplitude of the fast Na⁺ current. (B) Average AP parameters measured in five cells in presence of lidocaine. AP parameters are normalized to the AP parameters measured under baseline conditions in the same cell. (C) Typical APs of one atrial myocyte in absence (baseline) and presence of nifedipine to block the L-type Ca²⁺ current. (D) Average AP parameters measured in six cells in presence of nifedipine. AP parameters are normalized to the AP parameters measured under baseline conditions in the same cell. *p < 0.05, drug vs. baseline (paired t-test); ^# p < 0.05, drug effects observed with constant current, Bett current, and Kir2.1 current (ANOVA with follow-up test).