Cyclic AMP reverses the effects of aging on pacemaker activity and If in sinoatrial node myocytes

Figures

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  Figure 1.. Slower AP firing rates in aged SAMs persist during maximal stimulation of endogenous cAMP production. (A) Representative spontaneous APs from perforated-patch recordings from SAMs isolated from young (black) or aged (red) mice under control conditions (left) or in 100 µM IBMX plus 10 µM forskolin (Forsk; right). Scale bar: 250 ms, 50 mV. Dashed lines indicate 0 mV. (B) Mean AP firing rates (±SEM) from young and aged SAMs in control or IBMX plus forskolin. Numbers in parentheses indicate numbers of cells. *, P < 0.05 versus corresponding condition in young cells (t tests); ‡, P < 0.05 versus control conditions for the same age before wash on of IBMX/forskolin (paired t tests). (inset) Schematic illustration of perforated-patch recording configuration. Lightning bolts represent amphotericin B, and red asterisks represent endogenous cAMP remaining in the cell during the recordings.

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  Figure 2.. cAMP rescues the slower AP firing rate in aged SAMs. (A) Representative spontaneous APs from whole-cell recordings from SAMs isolated from young (black) or aged (red) mice under control conditions (left) or with 1 mM cAMP in the patch pipette (right). Scale bar: 250 ms, 50 mV. (B) Mean (±SEM) AP firing rates from whole-cell recordings from SAMs isolated from young (black) or aged (red) mice. Firing rates were recorded in control conditions (filled bars) or with 1 mM cAMP in the patch pipette (hatched bars). Numbers in parentheses indicate numbers of cells. P-values are from unpaired t tests. (inset) Schematic illustration of whole-cell recording configuration. Red asterisks represent cAMP introduced into the cell via the patch pipette in whole-cell recordings.

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  Figure 3.. Different effects of endogenous and exogenous cAMP on the voltage dependence of If in young and aged SAMs. (A and B) Normalized mean (±SEM) conductance-voltage relationships for If in whole-cell recordings from young (A) and aged (B) SAMs in control conditions (black and red symbols), in the presence of IBMX plus forskolin (white and pink) or with 1 mM cAMP in the patch pipette (gray and dark red). (insets) Representative whole-cell If current families. Scale bars: 500 pA, 500 ms (A) and 200 pA, 500 ms (B). (C) Mean (±SEM) V1/2 values for If in whole-cell recordings in control conditions (filled), with IBMX and forskolin in the bath (open), or with 1 mM cAMP in the patch pipette (hatched). *, P < 0.05 versus young SAMs in the same conditions (t tests); ‡, P < 0.05 versus control for the same age (ANOVAs with Holm-Šidák post-tests).

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  Figure 4.. Age-dependent changes in If in perforated-patch recordings. (A) Normalized mean (±SEM) conductance-voltage relationships for If in SAMs isolated from young (black) or aged (red) mice in amphotericin B perforated-patch recordings. (insets) Schematic illustration of perforated-patch recording configuration and representative perforated-patch If current families in young (black) or aged (red) SAMs. Scale bars: 500 pA, 500 ms. (B) Mean (±SEM) V1/2 values for If in young (black) and aged (red) SAMs in perforated-patch (PP, spotted bars) and whole-cell (WC, filled bars) recordings. P-values are comparisons between PP and WC for the same age (t tests); ‡, P < 0.05 compared with young in the same recording configuration (t tests).

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  Figure 5.. Age-dependent hyperpolarizing shift in the voltage dependence of If persists in excised inside-out patches but is rescued by cAMP. (A) Normalized mean (±SEM) conductance-voltage relationships for If 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 If current families recorded from patches from young (black) and aged (red) SAMs. (B) Mean (±SEM) V1/2 values for If 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).