Activation of smooth muscle and theories of contraction
Lazalde, Carlos Armando
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Permalink
https://hdl.handle.net/2142/23309
Description
Title
Activation of smooth muscle and theories of contraction
Author(s)
Lazalde, Carlos Armando
Issue Date
1992
Doctoral Committee Chair(s)
Barr, L.
Department of Study
Biophysics and Computational Biology
Discipline
Biophysics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Chemistry, Biochemistry
Biophysics, General
Language
eng
Abstract
We have analyzed the behavior of a linear, cyclic, four state model of regulation of contraction of smooth muscle. The model involves twenty one parameters: sixteen rate constants, three initial conditions, and NT$\sb3$ and NT$\sb4$, where N is the number of crossbridges, and T$\sb3$ and T$\sb4$ are the tension of phosphorylated and dephosphorylated crossbridges, respectively. The mathematical solution, for any state, is made of the sum of three weighted exponentials plus a constant term. The parameters can be obtained if transients of phosphorylation and tension are obtained, at two different concentrations of ATP, at least, with known ADP and Pi. If only data at one concentration of ATP is available, the model can be identified as a function of ten parameters: eight effective rate constants, and NT$\sb3$ and NT$\sb4$. We tested the model in four sets of published experimental data, by identifying the effective rate constants plus NT$\sb3$ and NT$\sb4$. The model was found to fit the data well, and the values of the parameters were apparently consistent with smooth muscle physiology, or plausible explanations could be postulated for their values. The ATP turnover energetic predictions of the model were off the experimental values by a factor of fifty, in one set where this test could be done. We conclude that, although the model fits the data well, because of its energetic failure, it must be considered with strong reservations as a possible good representation of real smooth muscle. A possible reason for the failure of the model is that it is too simple. Considerations of the disparity in the number of crossbridges vs. myosin light chain kinase molecules, suggests that models that recognize this disparity would involve a large number of states. These models could have a higher ATP turnover than four state models, but at a cost of requiring much increased mathematical complexity for their quantitative analysis.
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