Cross-bridge kinetics modeled from myoplasmic [Ca2+] and LV pressure at 17 degrees C and after 37 degrees C and 17 degrees C ischemia.
We modeled changes in contractile element kinetics derived from the cyclic relationship between myoplasmic [Ca(2+)], measured by indo 1 fluorescence, and left ventricular pressure (LVP). We estimated model rate constants of the Ca(2+) affinity for troponin C (TnC) on actin (A) filament (TnCA) and actin and myosin (M) cross-bridge (A x M) cycling in intact guinea pig hearts during baseline 37 degrees C perfusion and evaluated changes at 1) 20 min 17 degrees C pressure, 2) 30-min reperfusion (RP) after 30-min 37 degrees C global ischemia during 37 degrees C RP, and 3) 30-min RP after 240-min 17 degrees C global ischemia during 37 degrees C RP. At 17 degrees C perfusion versus 37 degrees C perfusion, the model predicted: A x M binding was less sensitive; A x M dissociation was slower; Ca(2+) was less likely to bind to TnCA with A x M present; and Ca(2+) and TnCA binding was less sensitive in the absence of A x M. Model results were consistent with a cold-induced fall in heart rate from 260 beats/min (37 degrees C) to 33 beats/min (17 degrees C), increased diastolic LVP, and increased phasic Ca(2+). On RP after 37 degrees C ischemia vs. 37 degrees C perfusion, the model predicted the following: A x M binding was less sensitive; A x M dissociation was slower; and Ca(2+) was less likely to bind to TnCA in the absence of A. M. Model results were consistent with reduced myofilament responsiveness to [Ca(2+)] and diastolic contracture on 37 degrees C RP. In contrast, after cold ischemia versus 37 degrees C perfusion, A x M association and dissociation rates, and Ca(2+) and TnCA association rates, returned to preischemic values, whereas the dissociation rate of Ca(2+) from A x M was ninefold faster. This cardiac muscle kinetic model predicted a better-restored relationship between Ca(2+) and cross-bridge function on RP after an eightfold longer period of 17 degrees C than 37 degrees C ischemia.
Rhodes
Samhita S
SS
Department of Biomedical Engineering, Marquette University, Milwaukee 53233, USA.
Ropella
Kristina M
KM
Audi
Said H
SH
Camara
Amadou K S
AK
Kevin
Leo G
LG
Pagel
Paul S
PS
Stowe
David F
DF
D000199:Actins / Q000378:metabolism; D000818:Animals; D001794:Blood Pressure; D002118:Calcium / Q000032:analysis* / Q000378:metabolism; D003080:Cold Temperature; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D006339:Heart Rate; D006358:Hot Temperature; D007211:Indoles; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D017202:Myocardial Ischemia / Q000503:physiopathology*; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology; D009206:Myocardium / Q000737:chemistry*; D009218:Myosins / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D019209:Troponin C / Q000378:metabolism; D016277:Ventricular Function, Left
D000199:Actins; D005456:Fluorescent Dyes; D007211:Indoles; D019209:Troponin C; D009218:Myosins; C048960:indo-1; D002118:Calcium