Disease relevance of SLC12A5

• The 5.9 kb hKCC2 transcript is specific to brain, and is induced during in vitro differentiation of NT2 teratocarcinoma cells into neuronal NT2-N cells [1].
• Targeted deletion of the neuronal-specific K-Cl cotransporter KCC2 generates mice with a profound seizure disorder and confirms the central role of this transporter in modulating neuronal excitability [2].
• In ganglion cells the upregulation of KCC2 by itself cannot explain the relatively fast switch in GABA's action; additional events, possibly KCC2's integration into the plasma membrane and downregulation of NKCC, might also contribute [3].
• These results suggest that KCC2, rather than NKCC1, mainly contributes to modulating excitability of the dorsal spinal cord neurons in the initial stage of formalin-evoked hyperalgesia [4].
• Reverse transcriptase-polymerase chain reaction revealed that KCC1 was present in rat primary astrocytes and rat C6 glioma cells but that KCC2 was completely absent from these cells, suggesting KCC2 was not of glial cell origin [5].

High impact information on SLC12A5

• NKCC1 expression level versus expression of the Cl(-)-extruding transporter (KCC2) in human and rat cortex showed that Cl(-) transport in perinatal human cortex is as immature as in the rat [6].
• These neurons are nocispecific, support long-term potentiation and appear to downregulate the K(+)-Cl(-) exporter channel KCC2 following peripheral nerve damage, leading to increased excitability [7].
• Removal of subplate neurons prevents the developmental upregulation of genes involved in mature, fast GABAergic transmission in cortical layer 4, including GABA receptor subunits and KCC2, and thus prevents the switch to a hyperpolarizing effect of GABA [8].
• In the spinal cord of wild-type animals, the KCC2 protein was found at inhibitory synapses [9].
• Several potassium-chloride cotransporters can lower the intracellular chloride concentration [Cl(-)](i), including the neuronal isoform KCC2 [9].

Biological context of SLC12A5

• The 24-exon SLC12A5 gene is on human chromosome 20q13, and contains a polymorphic dinucleotide repeat within intron 1 near a potential binding site for neuron-restrictive silencing factor [1].
• Initial and steady state kinetics of hKCC2-injected oocytes were performed in both isotonic and hypotonic conditions, revealing K(m)s for K(+) and Cl(-) of 9.3+/-1.8 mM and 6.8+/-0.9 mM, respectively; both affinities are significantly higher than KCC1 and KCC4 [1].
• Here we have determined chromosome location of both the human and the mouse genes encoding KCC2, which may assist in future efforts to determine the contribution of KCC2 to inherited human disorders [10].
• Quantitative RT-PCR analyses of the mRNAs extracted from the human TLE-associated brain regions revealed an up-regulation of NKCC1 mRNA and a down-regulation of KCC2 mRNA in the hippocampal subiculum, compared with the hippocampus proper or the TL neocortex, suggesting an abnormal transcription of Cl(-) transporters in the TLE subiculum [11].
• Mutagenesis of this region revealed that residues 1021-1035 of KCC2 are sufficient for isotonic transport [12].

Anatomical context of SLC12A5

• KCC2 (gene symbol SLC12A5) is expressed exclusively in neurons within the central nervous system and abnormalities in its expression have been proposed to play a role in pathological conditions such as epilepsy and neuronal trauma [10].
• In contrast, oocytes expressing mouse KCC4 do not mediate isotonic K-Cl cotransport but express much higher absolute transport activity than KCC2 oocytes under hypotonic conditions [1].
• The mRNA levels of NKCC1, an inwardly directed Na(+), K(+)-2Cl(-) cotransporter that facilitates the accumulation of intracellular Cl(-), and of KCC2, an outwardly directed K(+)-Cl(-) cotransporter that extrudes Cl(-), were studied in surgically resected brain specimens from drug-resistant temporal lobe (TL) epilepsy (TLE) patients [11].
• The KCC3 mRNA was highly expressed in brain, heart, skeletal muscle, and kidney, showing a distinct pattern and size from KCC1 and KCC2 [13].
• Finally, measurements of the GABA reversal potential in different starburst dendritic compartments indicate that the GABA reversal potential at the distal dendrite is more hyperpolarized than at the proximal dendrite due to KCC2 activity [14].

Associations of SLC12A5 with chemical compounds

• The relative expression level of the neuron-specific SLC12A5 and the Na(+)-K(+)-2Cl(-) cotransporter SLC12A2 appears to determine whether neurons respond to GABA with a depolarizing, excitatory response or with a hyperpolarizing, inhibitory response [15].
• The neuron-specific K(+)-Cl(-) cotransporter KCC2 plays a crucial role in determining intracellular chloride activity and thus the neuronal response to gamma-aminobutyric acid and glycine [12].
• Swelling-activated K(+)-Cl(-) cotransport is abrogated by calyculin A, whereas isotonic transport mediated by KCC chimeras and KCC2 is completely resistant to this serine-threonine phosphatase inhibitor [12].
• This conversion results from a gradual decrease in the chloride electrochemical equilibrium potential (ECl) of developing neurons, which correlates to an increase in the expression or activity of the potassium chloride cotransporter, KCC2 [16].
• Here we determined if the GABA switch correlates with the developmental expression patterns of KCC2, the chloride extruder K(+)-Cl(-) cotransporter, and NKCC, the chloride accumulator Na(+)-K(+)-Cl(-) cotransporter [3].

Regulatory relationships of SLC12A5

• Immunoblots of ferret retina showed that KCC2 upregulated in an exponential manner similar to synaptophysin (a synaptic marker) [3].

Other interactions of SLC12A5

• In addition, factors influencing the trafficking and kinetic modulation of KCC2 as well as activation/deactivation of CAVII are obvious candidates in the ionic modulation of GABAergic responses [17].
• Two developmental switches in GABAergic signalling: the K+-Cl- cotransporter KCC2 and carbonic anhydrase CAVII [17].
• KCC3 shares 75-76% identity at the amino acid level with human, pig, rat, and rabbit KCC1 and 67% identity with rat KCC2 [18].
• The down-regulation of KCC2 under pathophysiological conditions (epilepsy, damage) in mature neurones seems to reflect a 'recapitulation' of early developmental mechanisms, which may be a prerequisite for the re-establishment of connectivity in damaged brain tissue [17].
• We show here that selective blockade of the NKCC2 and KCC2 cotransporters located on starburst dendrites consistently hyperpolarized and depolarized the starburst cells, respectively, and greatly reduced or eliminated their directionally selective light responses [14].

Analytical, diagnostic and therapeutic context of SLC12A5

• Of the four KCC genes known to encode the respective proteins and their spliced variants, RT-PCR with both rat and human primers revealed the predicted cDNA fragments of KCC1, KCC3a, KCC3b, and KCC4 but not KCC2 in both HLE-B3 cells and in human lens tissue extracts from cataractous patients [19].
• Northern blot analysis using a KCC2-specific cDNA probe revealed a very highly expressed approximately5.6-kilobase transcript only in brain [5].
• In situ hybridization studies demonstrated that the KCC2 transcript was expressed at high levels in neurons throughout the central nervous system, including CA1-CA4 pyramidal neurons of the hippocampus, granular cells and Purkinje neurons of the cerebellum, and many groups of neurons throughout the brainstem [5].
• K-Cl cotransporter KCC2 immunohistochemistry revealed a developmental increase of staining in the area of lumbar motoneurons between P0 and P7 in cord-intact animals; this increase was not observed after spinal cord transection [20].
• To explore a possible role of KCC2-dependent inhibition in anesthetic-induced impairment of LTP, we used field excitatory postsynaptic potentials (fEPSP) recording and immunoblotting to study the effect of propofol on LTP maintenance and KCC2 expression in CA1 region of rat hippocampal slices [21].

References