Disease relevance of KCNJ13

• Expression of inward rectifier potassium channel Kir7.1 was confirmed in normal choroid plexus (34 of 35), choroid plexus papilloma (12 of 18), and choroid plexus carcinoma (5 of 5) but was not found in 100 other primary brain tumors and cerebral metastases [1].
• To conclude, the majority of PTPR can be distinguished from ependymomas and choroid plexus tumours by absent staining for epithelial membrane antigen, Kir7.1 and staniocalcin-1 as well as the presence of distinct MAP-2 immunoreactivity [2].

High impact information on KCNJ13

• In situ hybridization of rat brain sections demonstrated that Kir7.1 mRNA was absent from neurons and glia but strongly expressed in the secretory epithelial cells of the choroid plexus (as confirmed by in situ patch-clamp measurements) [3].
• When this residue was replaced by the conserved arginine in mutant Kir7.1 channels, the pronounced dependence of K+ permeability on [K+]e, characteristic for other Kir channels, was restored and the Ba2+ sensitivity was increased by a factor of approximately 25 (Ki = 27 microM) [3].
• In cRNA-injected Xenopus oocytes Kir7.1 generated macroscopic Kir currents that showed a very shallow dependence on external K+ ([K+]e), which is in marked contrast to all other Kir channels [3].
• At a holding potential of -100 mV, the inward current through Kir7.1 averaged -3.8 +/- 1.04 microA with 2 mM [K+]e and -4.82 +/- 1.87 microA with 96 mM [K+]e. Kir7.1 has a methionine at position 125 in the pore region where other Kir channels have an arginine [3].
• High levels of Kir7.1 transcripts were detected in rat brain, lung, kidney, and testis [3].

Biological context of KCNJ13

• Partial gene structure and assignment to chromosome 2q37 of the human inwardly rectifying K+ channel (Kir7.1) gene (KCNJ13) [4].
• 1. METHODS: Kir7.1 cDNA (1114 bp) was isolated from guinea pig kidney (gpKir7.1), and its tissue distribution was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) [5].

Anatomical context of KCNJ13

• Inwardly rectifying K+ channel Kir7.1 is highly expressed in thyroid follicular cells, intestinal epithelial cells and choroid plexus epithelial cells: implication for a functional coupling with Na+,K+-ATPase [6].
• Expression and permeation properties of the K(+) channel Kir7.1 in the retinal pigment epithelium [7].
• 2. The Kir7.1 channel current heterologously expressed in HEK293T cells (human embryonic kidney cell line) showed identical properties to those of the RPE IK(IR), i.e. poor dependence on [K+]o and low sensitivity to Ba2+ block [8].
• Among members of the inwardly rectifying K(+) channel family, we found with reverse transcriptase-polymerase chain reaction analyses that Kir4.1, Kir4.2 and Kir7.1 were expressed in rat gastric mucosa [9].
• In the brain inwardly rectifying potassium channel Kir7.1 subunits are predominantly expressed in the choroid plexus and meninges [10].

Associations of KCNJ13 with chemical compounds

• In epithelial Kir7.1 channels a non-conserved methionine in the outer pore region adjacent to the G-Y-G selectivity filter (position +2) was found to determine unique properties for permeant and blocking ions characteristic of a K(+) channel in a single-occupancy state [11].

Other interactions of KCNJ13

• In the isolated RPE cells, however, Kir4.1 immunoreactivity was largely lost, while Kir7.1 immunoreactivity remained [8].
• Our data suggest that antibodies directed against Kir7.1 and stanniocalcin-1 might serve as sensitive and specific diagnostic markers for choroid plexus tumors [1].

Analytical, diagnostic and therapeutic context of KCNJ13

• PCR analysis of monochromosomal and radiation hybrid panels assigns KCNJ13 to band 2q37 between markers D2S331 and D2S345 [4].
• 3. Expression of Kir7.1 mRNA and protein was detected in RPE cells by RT-PCR and immunoblot techniques, respectively [8].
• 4. Immunohistochemical studies including electron microscopy revealed that the Kir7.1 channel was localized specifically at the proximal roots of the apical processes of RPE cells, where Na+,K+-ATPase immunoreactivity was also detected [8].
• Immunohistochemistry and RT-PCR were used to localize Kir7.1 in guinea pig and human kidney [5].
• Human Kir7.1 channels were expressed in Xenopus oocytes and studied using the two-electrode voltage-clamp technique [7].

References