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Department of Diagnostic Radiology, Cardiovascular Sciences Research Group, University of Wales College of Medicine, Cardiff CF4 4XN, United Kingdom
We have developed a mathematical model of
arterial vasomotion in which irregular rhythmic activity is generated
by the nonlinear interaction of intracellular and membrane oscillators
that depend on cyclic release of
Ca2+ from internal stores and
cyclic influx of extracellular
Ca2+, respectively. Four key
control variables were selected on the basis of the pharmacological
characteristics of histamine-induced vasomotion in rabbit ear arteries:
Ca2+ concentration in the cytosol,
Ca2+ concentration in
ryanodine-sensitive stores, cell membrane potential, and the open state
probability of Ca2+-activated
K+ channels. Although not
represented by independent dynamic variables, the model also
incorporates
Na+/Ca2+
exchange, the
Na+-K+-ATPase,
Cl
fluxes, and
Ca2+ efflux via the extrusion
ATPase. Simulations reproduce a wide spectrum of experimental
observations, including 1) the
effects of interventions that modulate the functionality of
Ca2+ stores and membrane ion
channels, 2) paradoxes such as the
apparently unpredictable dual action of
Ca2+ antagonists and low
extracellular Na+ concentration,
which can abolish vasomotion or promote the appearance of
large-amplitude oscillations, and 3)
period-doubling, quasiperiodic, and intermittent routes to chaos.
Nonlinearity is essential to explain these diverse patterns of
experimental vascular response.
nonlinear dynamics; vasomotion; calcium channels; potassium channels; sodium/calcium exchange; calcium-adenosinetriphosphatase; sodium-potassium-adenosinetriphosphatase; chloride channels
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