AMPK activation inhibits I _f in female and male mouse pacemaker cells. (A–D) Whole-cell recordings of I_f in 3-mo-old female (A and B) and 3-mo-old male (C and D) mouse SAN cells in control (black) and after 4-h treatment with AMPK activator (AICAR 1 mM) (red). Data are obtained from N = 3 females and N = 3 males. (A and C) Representative current traces (left) and activation curves (right). Best fitting with the Boltzmann equation yielded the following values: (A) V1/2 = −91.0 ± 1.67; s = 8.2 ± 0.5 mV (n = 14) and V1/2 = −89.5 ± 1.69 mV; s = 7.5 ± 0.4 mV (n = 13) (n.s.); (C) V1/2 = −88.9 ± 1.76; s = 9.2 ± 0.5 mV (n = 12) and V1/2 = −88.2 ± 1.65 mV; s = 9.1 ± 0.7 mV (n = 15) (n.s.), for control and AICAR-treated cells, respectively. (B and D) Steady-state I/V relations; bar graphs on the left show the distributions of current densities at −125 mV. Predicted means ± SEM assuming GLMM (Gamma distribution) were (B) −35.4 ± 4.03 (n = 14) and −24.2 ± 2.87 pA/pF (n = 13) (P = 0.0982, n.s.); (D) −44.6 ± 5.49 (n = 12) and −25.2 ± 2.77 pA/pF (n = 15) (P = 0.0030, **) for control and AICAR-treated cells, respectively. The difference in current density in female vs. males did not reach significance (P = 0.05067). Significance P values were adjusted with Tukey’s test assuming four groups. Details of statistical analysis are shown in Table S1.