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

Abstract

Phosphorylation of brain Na ϩ channel ␣ subunits by cAMPdependent protein kinase (PKA) decreases peak Na ϩ current in cultured brain neurons and in mammalian cells and Xenopus oocytes expressing cloned brain Na ϩ channels. We have studied PKA regulation of Na ϩ 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 ϩ 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-␤-D-ribofuranosylbenzimidazole-3Ј,5Ј-monophosphorothioate (cBIMPS) and was inhibited by the specific PKA inhibitor peptide PKAI [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] . cBIMPS had similar effects on type IIA brain Na ϩ channel ␣ subunits expressed in tsA-201 cells, but no effect was observed on a mutant Na ϩ channel ␣ subunit in which serine residues in five PKA phosphorylation sites in the intracellular loop connecting domains I and II (L I-II ) had been replaced by alanine.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 L I-II of the Na ϩ channel ␣ subunit, causing a reduction in Na ϩ 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.

Effects of PKC and PKA Inhibitors on the cAMP-Stimulant-Induced Enhancement of Tetrodotoxin-Resistant Na+ (Nav1.8) Currents

“…Similarly, we found that application of 0.5 μM Ro-31-8425 application blocked an increase in Nav1.8 currents induced by either 8-Br-cAMP or the cAMP analogue forskolin [23]. This was supported by the fact that application of a PKC inhibitor (staurosporine or PKC [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] ) caused a marked inhibition of the forskolin-induced increase in the G V1/2 base (i.e. the percentage change in G at baseline V 1/2 ) [24,36,46].…”

“…The application of the PKC inhibitor PKC [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] significantly suppresses the forskolin-induced increase in the Nav1.8 current but the PKA inhibitor WIPTIDE has no significant effect on the PKC activator phorbol12, 13-dibutyrate (PDBu)-induced increase in the current [36]. When considering these results together, it is possible that PKCinduced phosphorylation of the channel protein at serine 1506 is required to enable PKA-induced phosphorylation of other sites on the channel protein suggested by Li et al [40] in a relationship between PKC and PKA on the convergent regulation of Na + channels.…”

“…The slow onset of Nav1.9 channel opening probably implies that this type of Na + channels makes a minor contribution to the action potential amplitude [25]. The majority of voltage-gated sodium channels (VGSCs) are inhibited by either protein kinase C (PKC) or protein kinase A (PKA) [26][27][28][29][30][31][32]. The VGSC into the skeletal and cardiac muscles is not significantly affected by the activation of PKA [33,34].…”

Ambient Light Regulates Sodium Channel Activity to Dynamically Control Retinal Signaling

“…Extracellular dopamine levels are low in dim conditions and are high in bright conditions (Boatright et al, 1989). Because the activity of voltage-gated sodium channels in other parts of the CNS is modulated by dopamine (Cantrell et al, 1997;Hayashida and Ishida, 2004), and dopamine receptors are present on bipolar cells (Veruki and Wassle, 1996;NguyenLegros et al, 1997;Mora-Ferrer et al, 1999), we investigated whether dopamine mediated the light-dependent modulation of the sodium channel activity by activating dopamine receptors in dim light with agonist applications.…”

“…Voltage-gated sodium channels are regulated by G-protein-coupled receptor (GPCR)-mediated phosphorylation (for review, see Cantrell and Catterall, 2001). Dopamine (Surmeier et al, 1992;Ma et al, 1994;Cantrell et al, 1997;Cantrell et al, 1999) and serotonin (Carr et al, 2003) modulate the generation of sodium spikes. However, it was not known whether EPSP amplification by sodium channels is affected by GPCR activation.…”