Figure 8. Bistability for Tightly Coupled Switches.

(A) Schematic of PSD-localised PP1 acting on both CaMKII and AMPAR substrates in the PSD. The asterisks on CaMKII and AMPAR represent phosphate groups.

(B) Time course of response to Ca²⁺ (2.7 μM, 500-s duration), then cAMP (0.108 μM, 2,000-s duration) stimuli. The initial Ca²⁺ stimulus turns on CaMKII transiently, but it eventually returns to baseline. The subsequent cAMP stimulus turns on both switches.

(C) Time course of response to cAMP (0.108 μM, 2,000-s duration), then Ca²⁺ (2.7 μM, 500-s duration) stimuli. The initial AMPAR stimulus (cAMP elevation) is sufficient to turn both the AMPAR and the CaMKII switches on.

(D) Stochastic run in the low state. The figure illustrates a transient event that did not result in complete turn on.

(E) Stochastic run in the high state. There is a spontaneous turn off, but the average on time is over 100 h.