Mechanism of constant contractile efficiency under cooling inotropy of myocardium: simulation

We have reported that, in canine hearts, cardiac cooling to 29°C enhanced left ventricular contractility but changed neither the contractile efficiency of cross-bridge (CB) cycling nor the excitation-contraction coupling energy. The mechanism of this intriguing energetics remained unknown. To get in...

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Bibliographic Details
Published in:American journal of physiology. Heart and circulatory physiology 1997-12, Vol.273 (6), p.H2891
Main Authors: Mikane, Takeshi, Araki, Junichi, Kohno, Kunihisa, Nakayama, Yasunori, Suzuki, Shunsuke, Shimizu, Juichiro, Matsubara, Hiromi, Hirakawa, Masahisa, Takaki, Miyako, Suga, Hiroyuki
Format: Article
Language:English
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Summary:We have reported that, in canine hearts, cardiac cooling to 29°C enhanced left ventricular contractility but changed neither the contractile efficiency of cross-bridge (CB) cycling nor the excitation-contraction coupling energy. The mechanism of this intriguing energetics remained unknown. To get insights into this mechanism, we simulated myocardial cooling mechanoenergetics using basic Ca and CB kinetics. We assumed that both adenosinetriphosphatase (ATPase)-dependent sarcoplasmic reticulum (SR) Ca uptake and CB detachment decelerated with cooling. We also assumed that all the ATPase-independent SR Ca release, Ca binding to and dissociation from troponin, and CB attachment remained unchanged. The simulated cooling shifted the CB force-free Ca concentration curve to a lower Ca concentration, increasing the Ca responsiveness of CB force generation, and increased the maximum Ca -activated force. The simulation most importantly showed that these cooling effects combined led to a constant contractile efficiency when Ca uptake and CB detachment rate constants changed appropriately. This result seems to account for our experimentally observed constant contractile efficiency under cooling inotropy.
ISSN:1522-1539