title: Modulation of force-frequency relation by phospholamban in genetically engineered mice.
abstract: Phospholamban levels regulate cardiac sarcoplasmic reticulum Ca2+ pump activity and myocardial contractility. To determine whether and to what extent phospholamban modulates the force-frequency relation and ventricular relaxation in vivo, we studied transgenic mice overexpressing phospholamban (PLBOE), gene-targeted mice without phospholamban (PLBKO), and isogenic wild-type controls. Contractility was assessed by the peak rate of left ventricular (LV) isovolumic contraction (+dP/dtmax), and diastolic function was assessed by both the peak rate (-dP/dtmax) and the time constant (tau) of isovolumic LV relaxation, using a high-fidelity LV catheter. Incremental atrial pacing was used to generate heart rate vs. -dP/dtmax (force-frequency) relations. Biphasic force-frequency relations were produced in all animals, and the critical heart rate (HRcrit) was taken as the heart rate at which dP/dtmax was maximal. The average LV +dP/dtmax increased in both PLBKO and PLBOE compared with their isogenic controls (both P < 0.05). The HRcrit for LV +dP/dtmax was significantly higher in PLBKO (427 +/- 20 beats/min) compared with controls (360 +/- 18 beats/min), whereas the HRcrit in PLBOE (340 +/- 30 beats/min) was significantly lower compared with that in isogenic controls (440 +/- 25 beats/min). The intrinsic heart rates were significantly lower, and the HRcrit and the +/-dP/dtmax at HRcrit were significantly greater in FVB/N than in SvJ control mice. We conclude that 1) the level of phospholamban is a critical negative determinant of the force-frequency relation and myocardial contractility in vivo, and 2) contractile parameters may differ significantly between strains of normal mice.
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati Medical Center, Cincinnati, Ohio 45267-0542, USA.
authors.forename: V J
authors.initials: VJ
authors.lastname: Kadambi
authors.forename: N
authors.initials: N
authors.lastname: Ball
authors.forename: E G
authors.initials: EG
authors.lastname: Kranias
authors.forename: R A
authors.initials: RA
authors.lastname: Walsh
authors.forename: B D
authors.initials: BD
authors.lastname: Hoit
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout / Q000235:genetics; D009200:Myocardial Contraction / Q000502:physiology*; D013045:Species Specificity; D000099211:Phospholamban
chemical_list: D002135:Calcium-Binding Proteins; D000099211:Phospholamban