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 (IKM), a sub-threshold voltage-dependent K+ current regulating neuronal excitability. In this study, we have investigated the involvement of IKM 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 IKM activator retigabine (0.01–30 μmol/L; Emax = 54.80 ± 3.85%; IC50 = 0.50 ± 0.36 μmol/L). The IKM 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 (Emax = 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 M1-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, IKM channels containing KCNQ2 subunits regulate depolarization-induced DA release and that IKM suppression is involved in the reinforcement of depolarization-induced DA release triggered by the activation of pre-synaptic muscarinic heteroreceptors.