Neuromedin U (NMU) plays very important roles in the central nervous system. However, to date, any role of NMU in hippocampal neurons and the relevant mechanisms still remain unknown. In the present study, we report that NMU selectively inhibits L-type high-voltage-gated Ca(2+) channels (HVGCC) in mouse hippocampal neurons, in which NMU type 1 receptor (NMUR1), but not NMUR2, is endogenously expressed. In wild type mice, NMU (0.1 microM) reversibly inhibited HVGCC barium currents (I(Ba)) by approximately 28%, while in NMUR1(-/-) mice NMU had no significant effects. Intracellular infusion of GDP-beta-S or a selective antibody raised against the G(o)alpha, as well as pretreatment of the neurons with pertussis toxin, blocked the inhibitory effects of NMU, indicating the involvement of G(o)-protein. This NMUR1-mediated effect did not display the characteristics of a direct interaction between G-protein betagamma subunit (G(betagamma)) and L-type HVGCC, but was abolished by dialyzing cells with QEHA peptide or an antibody to the G(beta). The classical and novel protein kinase C (PKC) antagonist calphostin C, as well as phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, abolished NMU responses, whereas the classical PKC antagonist Gö6976 had no such effects. Cells dialyzed with a PKC epsilon isoform (PKCepsilon) specific inhibitor peptide, GAVSLLPT, abolished NMU responses. In contrast, in cells dialyzed with an inactive PKCepsilon control scramble peptide, LSGTLPAV, no significant effects were observed. In summary, these results suggest that NMU inhibits L-type HVGCC via activation of NMUR1 and downstream G(betagamma), PI3K, and a novel PKCepsilon signaling pathway.
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