Figure 3. AMPAR and CaMKII Trafficking and Dependence on Steady Ca²⁺ Concentrations.

(A) Number of AMPARs in internal and synaptic membrane pools; AMPARs complexed to enzymes are not counted.

(B) Number of CaMKII molecules in the cytosol and PSD. The activity in the cytosol and PSD starts to rise at about 0.5 μM Ca²⁺, but translocation occurs around 1 μM.

(C) Conductance of membrane-inserted AMPARs. Receptor conductance is calculated by assuming that CaMKII phosphorylation of a single GluR1-Ser831 of the tetramer gives 1.5-fold basal conductance, and of two Ser831 gives 2-fold basal conductance. The conductance dips at around 300 nM Ca²⁺, when PP2B is active but CaMKII has yet to become fully active.