Figure 4.

Effects of activation of Na⁺‐K⁺‐ATPase by phosphorylated phos‐pholemman on β‐adrenergic response in vivo. Shown are normalized in vivo hemodynamics (+dP/dt) of anesthetized wild type (•; n= 9) and phospholemman‐null (€n= 14) mice after stimulation with 25 ng of isoproterenol. Note time‐dependent decline of +dP/dt in wild type but not phospholemman‐null hearts. Phospholemman phosphorylated at serine⁶⁸ activates Na⁺‐K⁺‐ATPase, ²⁵ , ³² leading to decreases in [Na⁺]_i in wild type but not phospholemman‐null cardiac myocytes. ³² , ⁷¹