Abstract
The beta-adrenergic signaling pathway regulates cardiac myocyte contractility
through a combination of feedforward and feedback mechanisms. We
used systems analysis to investigate how the components and topology
of this signaling network permit neurohormonal control of excitation-contraction
coupling in the rat ventricular myocyte. A kinetic model integrating
beta-adrenergic signaling with excitation-contraction coupling was
formulated, and each subsystem was validated with independent biochemical
and physiological measurements. Model analysis was used to investigate
quantitatively the effects of specific molecular perturbations. 3-Fold
overexpression of adenylyl cyclase in the model allowed an 85\% higher
rate of cyclic AMP synthesis than an equivalent overexpression of
beta 1-adrenergic receptor, and manipulating the affinity of Gs alpha
for adenylyl cyclase was a more potent regulator of cyclic AMP production.
The model predicted that less than 40\% of adenylyl cyclase molecules
may be stimulated under maximal receptor activation, and an experimental
protocol is suggested for validating this prediction. The model also
predicted that the endogenous heat-stable protein kinase inhibitor
may enhance basal cyclic AMP buffering by 68\% and increasing the
apparent Hill coefficient of protein kinase A activation from 1.0
to 2.0. Finally, phosphorylation of the L-type calcium channel and
phospholamban were found sufficient to predict the dominant changes
in myocyte contractility, including a 2.6x increase in systolic calcium
(inotropy) and a 28\% decrease in calcium half-relaxation time (lusitropy).
By performing systems analysis, the consequences of molecular perturbations
in the beta-adrenergic signaling network may be understood within
the context of integrative cellular physiology.
- activation;
- adenylate
- adrenergic,
- amp,
- amp-dependent
- analysis;
- animals;
- beta,
- biological;
- c,
- calcium
- calcium-binding
- chains;
- channels,
- chemical;
- cholera
- cyclase,
- cyclic
- cytology/metabolism;
- dose-response
- drug;
- enzyme
- factors
- humans;
- isoproterenol,
- kinase
- kinases,
- kinetics;
- l-type,
- markov
- metabolism;
- models,
- myocardium,
- pharmacology;
- phosphorylation;
- protein
- proteins,
- receptors,
- relationship,
- signal
- systems
- theoretical;
- time
- toxin,
- transduction;
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