Transient Calcium and Dopamine Increase PKA Activity and DARPP-32 Phosphorylation
Figure 10
Schematic Drawing of the Reactions Involved in the PKA–PP2A–phosphoThr75 Loop
When dopamine stimulates PKA, a substantial amount of the free catalytic subunit gets bound to PP2A and phosphoThr75, thus dampening the stimulatory effect of dopamine on PKA (A). Calcium stimulation and the formation of the calcium-activated PP2A affects this loop in two ways: 1) by increasing dephosphorylation of phosphoThr75, thus reducing inhibition of PKA; and 2) less PP2A is available for PKA binding, thus shifting this equilibrium to increase the amount of active PKA (B).