Dopaminergic Modulation of Sodium Current in Hippocampal Neurons via cAMP-Dependent Phosphorylation of Specific Sites in the Sodium Channel α Subunit

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Abstract
Phosphorylation of brain Na+ channel α subunits by cAMP-dependent protein kinase (PKA) decreases peak Na+ current in cultured brain neurons and in mammalian cells and Xenopus oocytes expressing cloned brain Na+ channels. We have studied PKA regulation of Na+ channel function by activation of D1-like dopamine receptors in acutely isolated hippocampal neurons using whole-cell voltage-clamp recording techniques. The D1 agonist SKF 81297 reversibly reduced peak Na+ current in a concentration-dependent manner. No changes in the voltage dependence or kinetics of activation or inactivation were observed. This effect was mediated by PKA, as it was mimicked by application of the PKA activator Sp-5,6-dichloro-1-β-d-ribofuranosylbenzimidazole-3′,5′-monophosphorothioate(cBIMPS) and was inhibited by the specific PKA inhibitor peptide PKAI5–24. cBIMPS had similar effects on type IIA brain Na+ channel α subunits expressed in tsA-201 cells, but no effect was observed on a mutant Na+ channel α subunit in which serine residues in five PKA phosphorylation sites in the intracellular loop connecting domains I and II (LI–II) had been replaced by alanine. A single mutation, S573A, similarly eliminated cBIMPS modulation. Thus, activation of D1-like dopamine receptors results in PKA-dependent phosphorylation of specific sites in LI–II of the Na+channel α subunit, causing a reduction in Na+current. Such modulation is expected to exert a profound influence on overall neuronal excitability. Dopaminergic input to the hippocampus from the mesocorticolimbic system may exert this influence in vivo.