Biomedical Engineering Reference
In-Depth Information
lationship between ATP and SSA for isometric contraction is
0
.
140
SSA
mG
AT P
.
V
beat
AT P
=
0
.
103
+
(7.20)
Taking into account the myosin ATPase concentration of 0.18 mol/m
3
(Velden et al.,
1998
) and free energy change during ATP hydrolysis of 60 kJ/mol (Gibbs and Bar-
clay,
1995
), the contraction efficiency calculated from the slope is 66 %. This value
is in good agreement with experimental data (Suga,
1990
), which demonstrates that
the chemomechanical efficiency of cross-bridge cycling is in the range of 60-70 %.
The set of free energy profiles simulated are shown in Fig.
7.4
(B). This set in-
volves a configuration chance for cross-bridges during the stroke by having different
free energy minimal location points for two strong binding biochemical states
S
1
and
S
2
. It is important to note that the set of parameters found by the optimization may
not be unique. In our work we tried to find cross-bridge rates with as simple shape
as possible to fit the desired data. It is possible to use different functional forms to
describe rate constants and still obtain good results.
7.5 Conclusion
Our mathematical model is able to replicate the classical measurements of SSA and
oxygen consumption dependency. As a result of optimization, the model solution
is in agreement with the behavior of cardiac muscle in isometric and shortening
contractions.
Acknowledgements
This research was supported by the European Union through the European
Regional Development Fund and by the Estonian Science Foundation (Grant nr. 7344).
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