Abstract 15890: Reduced Na/K Pump Current, Enhanced Contractility and Negative Force-frequency Relationship in Cardiomyocytes and Hearts Isolated from Mice Expressing Unphosphorylatable Phospholemman

Phospholemman (PLM) is a member of the FXYD family of Na/K ATPase accessory proteins expressed in cardiac tissue. It has been suggested that PLM phosphorylation provides the primary mechanism linking kinase activation to Na/K pump stimulation. PLM has previously been shown to be basally phosphorylated (by around 40%) and this can be further increased by PKC and/or PKA activation and by rapid pacing. Na/K pump current in myocytes isolated from PLM knock-out mice (PLMKO) is increased and, in isolated hearts, deletion of PLM causes a reduction in left ventricular pressure (LVDP) and a switch to a positive force-frequency gradient (FFRG) (cf a negative FFRG in WT hearts). To investigate the role of PLM phosphorylation a novel knock-in mouse (PLM-KI) was generated in which the endogenous allele was globally replaced with one expressing unphosphorylatable PLM (serines 63, 68 and 69 substituted with alanines). Na/K pump current was recorded using the perforated-patch technique in voltage-clamped myocytes isolate...