AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 5 978-R983, Copyright © 1986 by American Physiological Society
Modeling the contractility of urinary bladder smooth muscle using isometric contractions
R. van Mastrigt, J. W. Koopal, J. Hak and J. van de Wetering
In the course of developing a clinical contractility index, isometric
contractions of pig urinary bladder smooth muscle were analyzed in terms of
phase plots (a plot of the rate of change of a variable, in this case
force, as a function of the variable itself). The straight line describing
the major part of the phase plots is characterized by the two parameters
Fiso (the horizontal intercept) and c (the slope) of the line. It was found
that changes in the geometry of the tissue sample and changes in
extracellular calcium grossly influence Fiso, but not c, whereas changes in
prestimulus rest time influence c, but not Fiso. It is concluded that Fiso
is related to the number of available contractile units, and c is related
to the limiting rate constant in the excitation-contraction coupling, which
is probably determined by the release of intracellular calcium. The
existence of the calcium paradox and the interpretation of the concept of
facilitation or potentiation in this type of smooth muscle are discussed.
