Dopamine D3 receptor modulates D2 receptor effects on cAMP and GABA release at striatopallidal terminals—Modulation by the Ca2+–Calmodulin–CaMKII system

Dopamine D2 receptor (D2 R) is expressed in striatopallidal neurons and decreases forskolin-stimulated cyclic adenine monophosphate (cAMP) accumulation and gamma-aminobutyric acid (GABA) release. Dopamine D3 receptor (D3 R) mRNA is expressed in a population of striatal D2 R-expressing neurons. Also, D3 R protein and binding have been reported in the neuropil of globus pallidus. We explore whether D2 R and D3 R colocalize in striatopallidal terminals and whether D3 R modulates the D2 R effect on forskolin-stimulated [3 H]cAMP accumulation in pallidal synaptosomes and high K+ stimulated-[3 H]GABA release in pallidal slices. Previous reports in heterologous systems indicate that calmodulin (CaM) and CaMKII modulate D2 R and D3 R functions; thus, we study whether this system regulates its functional interaction. D2 R immunoprecipitates with CaM, and pretreatment with ophiobolin A or depolarization of synaptosomes with 15 mM of K+ decreases it. Both treatments increase the D2 R inhibition of forskolin-stimulated [3 H]cAMP accumulation when activated with quinpirole, indicating a negative modulation of CaM on D2 R function. Quinpirole also activates D3 R, potentiating D2 R inhibition of cAMP accumulation in the ophiobolin A-treated synaptosomes. D2 R and D3 R immunoprecipitate in pallidal synaptosomes and decrease after the kainic acid striatal lesion, indicating the striatal origin of the presynaptic receptors. CaM-kinase II alfa (CaMKIIα) immunoprecipitates with D3 R and increases after high K+ depolarization. In the presence of KN62, a CaMKIIα blocker, D3 R potentiates D2 R effects on cAMP accumulation in depolarized synaptosomes and GABA release in pallidal slices, indicating D3 R function regulation by CaMKIIα. Our data indicate that D3 R potentiates the D2 R effect on cAMP accumulation and GABA release at pallidal terminals, an interaction regulated by the CaM-CaMKIIα system.