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.