title: Ischemia reperfusion dysfunction changes model-estimated kinetics of myofilament interaction due to inotropic drugs in isolated hearts.
abstract: BACKGROUND
  The phase-space relationship between simultaneously measured myoplasmic [Ca2+] and isovolumetric left ventricular pressure (LVP) in guinea pig intact hearts is altered by ischemic and inotropic interventions. Our objective was to mathematically model this phase-space relationship between [Ca2+] and LVP with a focus on the changes in cross-bridge kinetics and myofilament Ca2+ sensitivity responsible for alterations in Ca2+-contraction coupling due to inotropic drugs in the presence and absence of ischemia reperfusion (IR) injury.
  
  
  METHODS
  We used a four state computational model to predict LVP using experimentally measured, averaged myoplasmic [Ca2+] transients from unpaced, isolated guinea pig hearts as the model input. Values of model parameters were estimated by minimizing the error between experimentally measured LVP and model-predicted LVP.
  
  
  RESULTS
  We found that IR injury resulted in reduced myofilament Ca2+ sensitivity, and decreased cross-bridge association and dissociation rates. Dopamine (8 microM) reduced myofilament Ca2+ sensitivity before, but enhanced it after ischemia while improving cross-bridge kinetics before and after IR injury. Dobutamine (4 microM) reduced myofilament Ca2+ sensitivity while improving cross-bridge kinetics before and after ischemia. Digoxin (1 microM) increased myofilament Ca2+ sensitivity and cross-bridge kinetics after but not before ischemia. Levosimendan (1 microM) enhanced myofilament Ca2+ affinity and cross-bridge kinetics only after ischemia.
  
  
  CONCLUSIONS
  Estimated model parameters reveal mechanistic changes in Ca2+-contraction coupling due to IR injury, specifically the inefficient utilization of Ca2+ for contractile function with diastolic contracture (increase in resting diastolic LVP). The model parameters also reveal drug-induced improvements in Ca2+-contraction coupling before and after IR injury.
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA. srhodes@mcw.edu
authors.forename: Samhita S
authors.initials: SS
authors.lastname: Rhodes
authors.forename: Amadou K S
authors.initials: AK
authors.lastname: Camara
authors.forename: Kristina M
authors.initials: KM
authors.lastname: Ropella
authors.forename: Said H
authors.initials: SH
authors.lastname: Audi
authors.forename: Matthias L
authors.initials: ML
authors.lastname: Riess
authors.forename: Paul S
authors.initials: PS
authors.lastname: Pagel
authors.forename: David F
authors.initials: DF
authors.lastname: Stowe
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002316:Cardiotonic Agents / Q000008:administration & dosage*; D003198:Computer Simulation; D004305:Dose-Response Relationship, Drug; D004360:Drug Therapy, Computer-Assisted / Q000379:methods; D006168:Guinea Pigs; D007700:Kinetics; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000187:drug effects*; D015427:Reperfusion Injury / Q000150:complications / Q000188:drug therapy / Q000503:physiopathology*; D016896:Treatment Outcome; D018487:Ventricular Dysfunction, Left / Q000188:drug therapy / Q000209:etiology / Q000503:physiopathology*
chemical_list: D002316:Cardiotonic Agents; D002118:Calcium