title: Tetrahydroberberine blocks ATP-sensitive potassium channels in dopamine neurons acutely-dissociated from rat substantia nigra pars compacta.
abstract: Tetrahydroberberine (THB) exhibits neuroprotective effects but its targets and underlying mechanisms are largely unknown. Emerging evidence indicates that ATP-sensitive potassium (K(ATP)) channels in the substantia nigra pars compacta (SNc) promote Parkinson disease (PD) pathogenesis, thus blocking K(ATP) channels may protect neurons against neuronal degeneration. In the present study, we tested a hypothesis that THB blocks K(ATP) channels in dopaminergic (DA) neurons acutely dissociated from rat SNc. Using perforated patch-clamp recording in current-clamp mode, the functional K(ATP) channels can be opened by persistent perfusion of rotenone, an inhibitor of complex I of the mitochondrial respiratory chain. Bath-application of THB reversibly blocks opened K(ATP) channels in a concentration-dependent manner, which is comparable to a classical K(ATP) channel blocker, Tol. Compared to THB analogs, l-stepholidine (l-SPD) or l-tetrahydropalmatine (l-THP), THB exhibits more profound blockade in K(ATP) channels. In addition, exposure of THB alone to the recorded neuron increases action potential firing, and THB also restores rotenone-induced membrane hyperpolarization in the presence of dopamine D2 receptor antagonist (sulpiride), suggesting that THB exhibits an excitatory effect on SNc DA neurons through the block of K(ATP) channels. Collectively, the blockade of neuronal K(ATP) channels by THB in SNc DA neurons is a novel pharmacological mechanism of THB, which may contribute to its neuroprotective effects in PD.
authors.affiliation: Division of Neurology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, 350 West Thomas Road, Phoenix, AZ 85013, USA.
authors.forename: Chen
authors.initials: C
authors.lastname: Wu
authors.forename: Kechun
authors.initials: K
authors.lastname: Yang
authors.forename: Qiang
authors.initials: Q
authors.lastname: Liu
authors.forename: Matoko
authors.initials: M
authors.lastname: Wakui
authors.forename: Guo-Zhang
authors.initials: GZ
authors.lastname: Jin
authors.forename: Xuechu
authors.initials: X
authors.lastname: Zhen
authors.forename: Jie
authors.initials: J
authors.lastname: Wu
mesh_terms: D000818:Animals; D001599:Berberine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D066298:In Vitro Techniques; D054086:KATP Channels / Q000037:antagonists & inhibitors*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D018696:Neuroprotective Agents / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D017448:Receptors, Dopamine D2 / Q000502:physiology; D013378:Substantia Nigra / Q000166:cytology / Q000187:drug effects* / Q000502:physiology
chemical_list: D054086:KATP Channels; D018696:Neuroprotective Agents; D017448:Receptors, Dopamine D2; D001599:Berberine; C004645:canadine; D004298:Dopamine