Involvement of KCNQ2 subunits in [H-3]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. [H-3]dopamine ([H-3]DA) release triggered by 9 mmol/L [K+](e) was inhibited by the I-KM activator retigabine (0.01-30 mu mol/L; E-max = 54.80 +/- 3.85%; IC50 = 0.50 +/- 0.36 mu mol/L). The I-KM blockers tetraethylammonium (0.1-3 mmol/L) and XE-991 (0.1-30 mu mol/L) enhanced K+-evoked [H-3]DA release and prevented retigabine-induced inhibition of depolarization-evoked [H-3]DA release. Retigabine-induced inhibition of K+-evoked [H-3]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 mu mol/L) potentiated 9 mmol/L [K+](e)-evoked [H-3]DA release (E-max = 155 +/- 9.50%; EC50 = 25 +/- 1.80 mu mol/L). OXO (100 mu mol/L)-induced [H-3]DA release enhancement was competitively inhibited by pirenzepine (1-10 nmol/L) and abolished by the M-3-preferring antagonist 4-diphenylacetoxy N-methylpiperidine methiodide (1 mu mol/L), but was unaffected by the M-1-selective antagonist MT-7 (10-100 nmol/L) or by Pertussis toxin (1.5-3 mu g/mL), which uncouples M-2- and M-4-mediated responses. Finally, OXO-induced potentiation of depolarization-induced [H-3]DA release was not additive to that produced by XE-991 (10 mu mol/L), was unaffected by retigabine (10 mu mol/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.