Inward rectifier potassium channels are characterized by a greater tendency to allow potassium to flow into the cell rather than out of it. Their voltage dependence is regulated by the concentration of extracellular potassium; as external potassium is raised, the voltage range of the channel opening shifts to more positive voltages. The inward rectification is mainly due to the blockage of outward current by internal magnesium.
Catalysis of the transmembrane transfer of a potassium ion by an inwardly-rectifying voltage-gated channel. An inwardly rectifying current-voltage relation is one where at any given driving force the inward flow of K+ ions exceeds the outward flow for the opposite driving force. The inward-rectification is due to a voltage-dependent block of the channel pore by a specific ligand or ligands, and as a result the macroscopic conductance depends on the difference between membrane voltage and the K+ equilibrium potential rather than on membrane voltage itself.
J. Biol. Chem. 272, 586-593 (1997)[PubMed:8995301]
The DNA sequence encoding the rat brain inward rectifier-10 K+ channel was amplified from rat brain RNA using reverse transcription-polymerase chain reaction and used to clone the human homolog. Low stringency screening of a human kidney cDNA library and subsequent DNA sequence analysis identified two related K+ inward rectifier cDNAs, referred to as Kir1.2 and Kir1.3, which were derived from transcription of distinct human genes. Kir1.2 represents the human homolog of the rat BIRK-10 sequence, whereas Kir1.3 was unique compared with all available sequence data bases. The genes that encode Kir1.2 and Kir1.3 were mapped to human chromosomes 1 and 21, respectively. Both genes showed tissue-specific expression when analyzed by Northern blots. Kir1.2 was only detected in brain >> kidney and was detected at high levels in all brain regions examined. Kir1.3 was most readily detected in kidney and was also expressed in pancreas > lung. Comparative analysis of the predicted amino acid sequences for Kir1.2 and Kir1.3 revealed they were 62% identical. The most remarkable difference between the two polypeptides is that the Walker Type A consensus binding motif present in both Kir1.1 and Kir1.2 was not conserved in the Kir1.3 sequence. Expression of the Kir1.2 polypeptide in Xenopus oocytes resulted in the synthesis of a K+-selective channel that exhibited an inwardly rectifying current-voltage relationship and was inhibited by external Ba2+ and Cs+. Kir1.2 current amplitude was reduced by >85% when the pH was decreased from pH 7.4 to 5.9 using the membrane-permeant buffer acetate but was relatively unaffected when pH was similarly lowered using membrane-impermeant biphthalate. The inhibition by intracellular protons was voltage-independent with an IC50 of pH 6.2 and a Hill coefficient of 1.9, suggesting the cooperative binding of 2 protons to the intracellular face of the channel. In contrast, Kir1.3 expression in Xenopus oocytes was not detectable despite the fact that the cRNA efficiently directed the synthesis of a polypeptide of the expected Mr in an in vitro translation system. Co-expression of Kir1.3 with either Kir1.1 or Kir1.2 reduced currents resulting from expression of these inward-rectifier subunits alone, consistent with a dominant negative influence on Kir1.1 and Kir1.2 expression.
Protein involved in the transport of ions. Such proteins are usually transmembrane and mediate a movement of ions across cell membranes. Transport may be passive (facilitated diffusion; down the electrochemical gradient), or active (against the electrochemical gradient). Active transport requires energy which may come from light, oxidation reactions, ATP hydrolysis, or cotransport of other ions or molecules.
Protein involved in the transport of a molecule (metabolite, protein, etc), a ion or an electron across cell membranes, inside the cell or in a tissue fluid.
Protein which is part of a transmembrane protein complex that forms a hydrophilic channel across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients. The channels are usually gated and only open in response to a specific stimulus, such as a change in membrane potential (voltage-gated) or the binding of a ligand (ligand-gated channel).
Protein which is a component of a voltage-gated channel. Voltage-gated ion channels are responsible for the electrical activity in a variety of cell types. They probably exist in all life forms.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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