title: Melatonin-mediated inhibition of Purkinje neuron P-type Ca²⁺ channels in vitro induces neuronal hyperexcitability through the phosphatidylinositol 3-kinase-dependent protein kinase C delta pathway.
abstract: Although melatonin receptors are widely expressed in the mammalian central nervous system and peripheral tissues, there are limited data regarding the functions of melatonin in cerebellar Purkinje cells. Here, we identified a novel functional role of melatonin in modulating P-type Ca(2+) channels and action-potential firing in rat Purkinje neurons. Melatonin at 0.1 μm reversibly decreased peak currents (I(Ba)) by 32.9%. This effect was melatonin receptor 1 (MT(R1)) dependent and was associated with a hyperpolarizing shift in the voltage dependence of inactivation. Pertussis toxin pretreatment, intracellular application of QEHA peptide, and a selective antibody raised against the Gβ subunit prevented the inhibitory effects of melatonin. Pretreatment with phosphatidylinositol 3-kinase (PI3K) inhibitors abolished the melatonin-induced decrease in I(Ba). Surprisingly, melatonin responses were not regulated by Akt, a common downstream target of PI3K. Melatonin treatment significantly increased protein kinase C (PKC) activity 2.1-fold. Antagonists of PKC, but not of protein kinase A, abolished the melatonin-induced decrease in I(Ba). Melatonin application increased the membrane abundance of PKCδ, and PKCδ inhibition (either pharmacologically or genetically) abolished the melatonin-induced IBa response. Functionally, melatonin increased spontaneous action-potential firing by 53.0%; knockdown of MT(R1) and blockade of P-type channels abolished this effect. Thus, our results suggest that melatonin inhibits P-type channels through MT(R1) activation, which is coupled sequentially to the βγ subunits of G(i/o)-protein and to downstream PI3K-dependent PKCδ signaling. This likely contributes to its physiological functions, including spontaneous firing of cerebellar Purkinje neurons.
authors.affiliation: Department of Neurobiology, Medical College of Soochow University, Suzhou, China; Department of Geriatrics and Institute of Neuroscience, The Second Affiliated Hospital of Soochow University, Suzhou, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Yicheng
authors.initials: Y
authors.lastname: Pu
authors.forename: Shan
authors.initials: S
authors.lastname: Gong
authors.forename: Chunfeng
authors.initials: C
authors.lastname: Liu
authors.forename: Xinghong
authors.initials: X
authors.lastname: Jiang
authors.forename: Jin
authors.initials: J
authors.lastname: Tao
mesh_terms: D000818:Animals; D020865:Calcium Channels, P-Type / Q000187:drug effects* / Q000378:metabolism; D008550:Melatonin / Q000494:pharmacology*; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism*; D051745:Protein Kinase C-delta / Q000378:metabolism*; D011689:Purkinje Cells / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D020865:Calcium Channels, P-Type; D058539:Phosphatidylinositol 3-Kinase; D051745:Protein Kinase C-delta; D008550:Melatonin
keywords: P-type calcium channel; Purkinje neuron; melatonin; protein kinase C