ilya_prigogine_isabelle_stengers_alvin_tofflerbookfi-org

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158
cAMP synthesis has permitted unification of different types of behavior observed
during aggregation.se
Two key parameters of the model are the concentrations of adenylate
cyclase (s) and of phosphodiesterase (k). Figure C (redrawn from A. GoLD·
BETER and L. SEGEL, Differentiation, Vol. 17 [1980], pp. 127-35), shows the
behavior of the modelized system in the space formed by s and k.
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Phosphodiesterase ,
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Figure C
Three regions can be distinguished for different values of k and s. Region
A corresponds to a stable, nonexcitable stationary state; region B to a stationary
state stable but excitable: the system is capable of amplifying small
perturbations in the concentration of cAMP in a pulsatory manner (and thus
of relaying cAMP signals); region C corresponds to a regime of sustained
oscillations around an unstable stationary state.
The arrow indicates a possible "developmental path" corresponding to a
rise in phosphodiesterase (k) and adenylate cyclase (s), a rise that is observed
to occur after the beginning of starvation. The crossing of regions A,
B and C corresponds to the observed change of behavior: cells are at first
incapable of responding to extracellular cAMP signals; thereafter they relay
these signals and, finally, they become capable of synthetizing them periodically
in an autonomous way. The aggregation centers would thus be the
cells for which the parameters s and k have reached the more rapidly a point
located inside region 0 after starvation has begun.