Specific Modulation of Na⁺Channels in Hippocampal Neurons by Protein Kinase Cϵ

Abstract

Acetylcholine binding to muscarinic acetylcholine receptors activates G-proteins, phospholipase C, and protein kinase C (PKC), which phosphorylates brain Na ϩ channels and reduces peak Na ϩ current in hippocampal neurons. Because multiple PKC isozymes with different regulatory properties are expressed in hippocampal neurons, we investigated which ones are responsible for mediating this effect. The diacylglycerol analog oleoylacetylglycerol (OAG) reduced the amplitude of Na ϩ current in dissociated mouse hippocampal neurons by 28.5 Ϯ 5.3% ( p Ͻ 0.01). The reduction of peak Na ϩ current was similar with Ca 2ϩ -free internal solution and in 92 nM internal Ca 2ϩ , suggesting that calcium-dependent, conventional PKC isozymes were unlikely to mediate this response. Gö6976, which inhibits conventional PKC isozymes, reduced the effect of PKC activators only slightly, whereas rottlerin, which inhibits PKC␦ preferentially at 5 M, had no effect. Ro-31-8425 (20 nM), which inhibits conventional PKC isozymes, did not reduce the response to OAG. However, higher concentrations of Ro-31-8425 (100 nM or 1 M) that inhibit novel PKC isozymes effectively blocked OAG inhibition of Na ϩ current. Inclusion of a selective PKC⑀-anchoring inhibitor peptide (PKC⑀-I) in the recording pipette prevented the reduction of peak Na ϩ current by OAG, whereas an anchoring inhibitor peptide specific for PKC␤ and an inactive scrambled PKC⑀-I peptide had no effect. In addition, OAG had no effect on Na ϩ current in hippocampal neurons from PKC⑀ null mice. Overall, our data from four experimental approaches indicate that anchored PKC⑀ is the isozyme responsible for PKC-mediated reduction of peak Na ϩ currents in mouse hippocampal neurons.

Modulation of h-Channels in Hippocampal Pyramidal Neurons by p38 Mitogen-Activated Protein Kinase

“…Setting our search parameters at the highest level of stringency produced the list of 12 kinases shown in Table 1. Of this list, three kinases had previously described actions on voltage-gated ion channels: protein kinase C (PKC), calcium/calmodulin-dependent protein kinase II (CAMKII), and p38 MAPK (Varga et al, 2004;Chen et al, 2005;Wittmack et al, 2005). Of the entire list, p38 MAPK had the highest score for likely HCN interactions, and was predicted to phosphorylate both HCN1 and HCN2.…”

No oxygen? No problem! Intrinsic brain tolerance to hypoxia in vertebrates

“…The selective peptide inhibitor of εPKC (eV1-2) shortened the time to ID in brain slices from AGSs but not in rats even though εV1-2 decreased activation of εPKC in brain slices from both species. Activation of εPKC inhibits Na + /K + ATPase and voltage-gated sodium channels (Chen et al, 2005;Nowak et al, 2004), both of which contribute to the collapse of ion homeostasis during ischemia and may be targets of εPKC during cerebral ischemia in AGSs (Dave et al, 2009). Blocking or delaying the ID can significantly improve recovery (Anderson et al, 2005;Takeda et al, 2003).…”

Homeostatic Regulation of Intrinsic Excitability and Synaptic Transmission in a Developing Visual Circuit

“…Between stages 44 -46 and stage 49, the observed decrease in peak Na ϩ current amplitude could be attributable to a change in the density of voltage-gated Na ϩ channels or to a change in their modulation (Huguenard et al, 1988;Bevan and Storey, 2002;Chen et al, 2005). The fact that the decrease in the peak Na ϩ current is accompanied by an increase in the spike rise time and rate of rise ( Table 1), suggests that a change in the number of functional channels is the likely mechanism underlying a decrease in spike rate.…”