Age-dependent hyperpolarizing shift in the voltage dependence of I_f persists in excised inside-out patches but is rescued by cAMP. (A) Normalized mean (±SEM) conductance-voltage relationships for I_f from excised inside-out patches in SAMs isolated from young (black) and aged (red) mice in control conditions (filled) or upon wash-on of cAMP (open). (insets) Schematic illustration of excised patch recording configuration and representative I_f current families recorded from patches from young (black) and aged (red) SAMs. (B) Mean (±SEM) V_1/2 values for I_f in young (black) and aged (red) SAMs in control conditions (filled bars) and in the presence of 100 µM cAMP (hatched bars). *, P < 0.05 compared versus young control (t tests).