Figure 5.

(A) ∂a/∂t versus a for an isolated cell with h = 0 or u ≫ U. At low A_a bistability exists even when h=0. At high A_a there is no bistability. At intermediate values bistability can exist for some amount of external activation. (B) Steady states of a as a function of the input $g(h,u)=g_{m_h,m_u}\left(\frac{h}{H},\frac{u}{U}\right)$. (C) Steady states of a including the effects of self-u (see Eq. 9), plotted as a function of the activating input ḡ(h). The cell is assumed to receive negligible u from other cells. As A_u decreases, the high steady state eventually becomes completely inaccessible to cells starting from a=0, even when h is very large. Parameters: G = 1; n_a = 4. In (C), A_a = 0.35; U = 0.0001; n_u = 8; m_u = 8.