Involvement of KCNQ2 subunits in [3H]dopamine release triggered by depolarization and pre-synaptic muscarinic receptor activation from rat striatal synaptosomes

KCNQ2 and KCNQ3 subunits encode for the muscarinic-regulated current (I_KM), a sub-threshold voltage-dependent K⁺ current regulating neuronal excitability. In this study, we have investigated the involvement of I_KM in dopamine (DA) release from rat striatal synaptosomes evoked by elevated extracellular K⁺ concentrations ([K⁺]_e) and by muscarinic receptor activation. [ ³H]dopamine ([³H]DA) release triggered by 9 mmol/L [K ⁺]_e was inhibited by the I_KM activator retigabine (0.01-30 μmol/L; E_max = 54.80 ± 3.85%; IC ₅₀ = 0.50 ± 0.36 μmol/L). The I_KM blockers tetraethylammonium (0.1-3 mmol/L) and XE-991 (0.1-30 μmol/L) enhanced K ⁺-evoked [³H]DA release and prevented retigabine-induced inhibition of depolarization-evoked [³H]DA release. Retigabine-induced inhibition of K⁺-evoked [³H]DA release was also abolished by synaptosomal entrapment of blocking anti-KCNQ2 polyclonal antibodies, an effect prevented by antibody pre-absorption with the KCNQ2 immunizing peptide. Furthermore, the cholinergic agonist oxotremorine (OXO) (1-300 μmol/L) potentiated 9 mmol/L [K⁺]_e-evoked [ ³H]DA release (E_max = 155 ± 9.50%; EC₅₀ = 25 ± 1.80 μmol/L). OXO (100 μmol/L)-induced [³H]DA release enhancement was competitively inhibited by pirenzepine (1-10 nmol/L) and abolished by the M₃-preferring antagonist 4-diphenylacetoxy N-methylpiperidine methiodide (1 μmol/L), but was unaffected by the M ₁-selective antagonist MT-7 (10-100 nmol/L) or by Pertussis toxin (1.5-3 μg/mL), which uncouples M₂- and M₄-mediated responses. Finally, OXO-induced potentiation of depolarization-induced [ ³H]DA release was not additive to that produced by XE-991 (10 μmol/L), was unaffected by retigabine (10 μmol/L), and was abolished by synaptosomal entrapment of anti-KCNQ2 antibodies. Collectively, these findings indicate that, in rat striatal nerve endings, I_KM channels containing KCNQ2 subunits regulate depolarization-induced DA release and that I _KM suppression is involved in the reinforcement of depolarization-induced DA release triggered by the activation of pre-synaptic muscarinic heteroreceptors.