Fig. 8
γ2 AMPK is critically required for the intrinsic bradycardic adaptation to endurance exercise. a Results of western blot analysis of α AMPK Thr172 phosphorylation in whole heart tissue from sedentary (S) and exercised (Ex, 10 weeks of voluntary wheel running) WT Cre+ mice (n = 8–10). b–d Average daily distance (b), time (c), and speed (d) of voluntary wheel running during a 10–week training period of WT Cre+ and Homo fl Cre+ mice (n = 17–26). e Spontaneous beating rate of isolated intact SA node/atrial preparations from S and Ex WT Cre+ and Homo fl Cre+ mice (n = 10–22). f Representative action potentials recorded from isolated SA cells. g Mean beating rate of isolated SA cells from S and Ex groups (n = 12–27 cells). h Representative SA cell I f traces during steps to −125 mV. i Mean fully activated I/V curves recorded in SA cells. Linear data fitting yielded statistically significant differences (P < 0.0001) in I f slope conductance of SA cells from exercised WT Cre+ mice only, with conductance values of 481 (S WT Cre+), 447 (S Homo fl Cre+), 272 (Ex WT Cre+) and 447 pS/pF (Ex Homo fl Cre+) (n = 6–14 cells/4–8 mice per group). j Mean voltage-dependence of I f activation of SA cells from both S and Ex groups (n = 6–15). k Schematic depicting the central function of SA cell γ2 AMPK in overall cardiac energy accounting. a–d Student’s t-test was performed; e, g, one-way ANOVA followed by (e) Holm–Sidak’s multiple comparisons test or (g) Fisher’s least significant difference test was performed. *P < 0.05, **P < 0.01, ξ P < 0.0001 for both Ex WT Cre+ vs S Homo fl Cre+ and Ex WT Cre+ vs Ex Homo fl Cre+ comparisons. a–e, g Data are shown as means ± s.e.m.
