O ATP and Glu release inside the periaxonal space (Figure 1B, see also paragraph Signals transmitted by active axons) (Verderio et al., 2006; Fields and Ni, 2010; Wake et al., 2011). By activating P2Y and AMPA receptors on iSCs and nmSCs, these neurotransmitters reciprocally trigger secretion of ATP along with the excitatory amino acids Glu and aspartate from SCs, through ion channels or vesicular mechanisms (Figures 1F1,F2) (Jeftinija and Jeftinija, 1998; Liu and Bennett, 2003; Liu et al., 2005). SCs may also secrete the inhibitory neurotransmitter GABA, recognized to modulate peripheral fiber excitability, but whether or not its secretion is induced by neuronal activity has not been determined (Morris et al., 1983; Carr et al., 2010; Magnaghi et al., 2010). SC-released neurotransmitters exert local effects on axonal excitability (Carlton et al., 2001; Irnich et al., 2001) (Figure 1F3). Additionally, they might initiate signals that propagate electrically or via retrograde axonal transport toward neuronal cell bodies, affecting soma signaling processes and gene sn-Glycerol 3-phosphate Purity & Documentation Expression (Itoh et al., 1997; Amir and Devor, 2003; Chen et al., 2012).SC differentiation and myelinationMyelin production by SCs results in the organization of enwrapped axons into distinct structural domains with very specialized patterns of ion channel expression (Salzer, 2003; Buttermore et al., 2013). Internodes, electrically insulated by myelin layers with low electrical capacitance, alternate with ion-rich nodes of Ranvier, exactly where APs are generated, so that rapid and power effective saltatoryFrontiers in Cellular Neurosciencewww.frontiersin.orgNovember 2013 | Volume 7 | Write-up 228 |Table 1 | Expression and regulation of potential SC activity sensors. Subtypes Throughout development Previously published dataa-o Up Kv1.1, Kv1.2, Kv1, Kv5.1, Kv7 .5 Kv2.1, Kv3, Kv3.four, minK-like Kv7 .5 Kv1.six Down Up Delayed rectifier, A-type, outward-rectifying, inward-rectifying, slowly activating Kv1.1, Kv1.two,Kv1.five, Kv1.four, Kv2.1, Kv3.1b, Kv3.two,Kv7 Kv7 in iSCs .three, .5 or SN, inactivating A-type and delayed-rectifier current in soma Kir2.1IRK1, Kir2.3,IRK3, in nmSC soma and mSC microvilli Maxi-K+ present in iSC KCa1.1, KCa4.1 soma SK channel KCa2.2, KCa2.three, KCa3.1 Twik-1, Trek-1, Task-2, Twik-2, Thick1 Nav1, Nav2, Nav3, Nav4 NavX Cav3.1 (low), Cav3.two KCa3.1 KCa3.1 KCa3.1 Kir6.1UKATP-1 Kir6.1 KCa4.1 Kir4.1 Kir2.2IRK2 Kir2.2IRK2 Kv1.1, Kv1.two, Kv1.6, Kv2.1, Kv1, Kv2, Kv3, minK-like, Kv5.1 Kv7 Kv11.1, .5, Kv11.three, Kv6.two Microarray datap Expression in SCs Transcriptional regulation p In neuropathy models DownSamara et al.FamiliesFrontiers in Cellular Neuroscience IRK, Kir2.x, subfamily J Kir2.two IRK2 Kir4.x Kir6.x, KATP ATP-sensitive , BK channel Kir6.1 KCa1.1 TWIK, TREK, Task, Talk, THIK, TRESK Twick-1, Thick-1, Twick-2, Task-1 Trek-1, Task-2, Task-1 Nav1 Nav3 Twick-1, Trek-1 TTX-sensitive Nav1.2,3,7 in iSCs, present in iSC soma Existing in iSC soma NavX in iSCs and nmSCs Present in iSC soma Nav1 TTX-resistant NaG T-type VGCCs NavX Cav3.2 Cav3.2 NavX L-type PQ Auxiliary subunits Current in iSC soma Cav1.1 Cav2.1 1, 1, 3, 4, 21 three 1 (Continued)Potassium channelsa,bVoltage-gatedInwardly 7α-Hydroxy-4-cholesten-3-one Endogenous Metabolite rectifyingwww.frontiersin.orgCalcium activatedTandem pore domainVoltage-gated sodium channelsa,bVoltage-gated calcium channelsa,bAlpha subunitsPNS glia-neuron communicationNovember 2013 | Volume 7 | Report 228 |Auxiliary subunitsSamara et al.Table 1 | Continued Subtypes Through development Previously published dataa-o Up Clcn2, Clcn3 VDAC1 Down Up Voltage-g.