Figure 2.

Bistability characteristics of the αCaMKII–CPEB1-positive feedback loop. A brief (Ca²⁺)₄–CaM concentration pulse is used to mimic the induction of L-LTP through the application of HFS. The solid line represents the αCaMKII concentration at the basal level (without the application of pulse) and the dashed line represents the αCaMKII concentration after the application of pulse. (A) Total αCaMKII concentration (μM) with a lower steady state at 10 μM and an upper steady state at ∼22 μM. (B) Fraction of active and phosphorylated αCaMKII with a lower steady state at ∼0 and an upper steady state at ∼25%. This figure also shows the bistability characteristics of the αCaMKII–CPEB loop at different amplitudes of the (Ca²⁺)₄–CaM pulse for 10 s duration. These results show that even with different amplitudes of pulse stimulus, the αCaMKII–CPEB loop converges to the same up- or downregulated state, thus indicating that this system is bistable, that is, with a sufficiently strong stimulus, it is upregulated and without enough stimulus it is downregulated.