Figure 2. Repolarizing K⁺ current amplitudes and densities were increased in LV myocytes isolated from swim-trained Akt1^−/− animals.

(A) Representative whole-cell K⁺ currents, recorded from myocytes isolated from the LV apex of swim-trained and untrained C57Bl/6 Akt1^−/− mice, are illustrated. Currents were evoked in response to (4.5 s) voltage steps to test potentials between −120 and +40 mV from a holding potential (HP) of −70 mV. (B) The mean ± SEM amplitudes of the peak outward K⁺ currents were significantly (^#P<0.01,^*P<0.001) higher in LV apex myocytes from swim-trained, compared with untrained Akt1^−/− animals. (C) Mean ± SEM whole-cell membrane capacitances (C_m) were similar in LV myocytes isolated from swim-trained and untrained Akt1^−/− animals, consistent with the absence of hypertrophic growth in response to exercise training. (D) Normalizing current amplitudes to cell size (C_m) revealed that mean ± SEM I_K,peak densities were also significantly higher in LV apex myocytes from swim-trained, compared with untrained, Akt1^−/− animals. (E) Representative whole-cell K₊ currents, recorded from myocytes isolated from the LV apex of swim-trained and untrained WT (C57Bl/6) mice, are illustrated. (F) The mean ± SEM amplitudes of the peak outward K⁺ currents (I_K,peak) were significantly (^#P<0.01) higher in LV apex myocytes from swim-trained, compared with untrained, WT (C57Bl/6) animals. (G) Mean ± SEM whole-cell C_m were significantly (^‡P<0.05) higher in LV myocytes isolated from swim-trained, compared to untrained, WT (C57Bl/6) animals, consistent with the development of hypertrophic growth in response to chronic swim training. (H) Normalizing current amplitudes to whole-cell membrane capacitance revealed that mean ± SEM I_K,peak densities were also significantly higher in LV apex myocytes from swim-trained, compared with untrained, WT animals.