Cloning and characterization of two K+ inward rectifier (Kir) 1.1 potassium channel homologs from human kidney (Kir1.2 and Kir1.3).
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.
Shuck
M E
ME
Department of Cell Biology and Inflammation Research, Pharmacia & Upjohn, Inc., Kalamazoo, Michigan 49007, USA.
Piser
T M
TM
Bock
J H
JH
Slightom
J L
JL
Lee
K S
KS
Bienkowski
M J
MJ
D000595:Amino Acid Sequence; D000818:Animals; D002878:Chromosomes, Human, Pair 1; D002891:Chromosomes, Human, Pair 21; D003001:Cloning, Molecular; D004553:Electric Conductivity; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007668:Kidney; D008562:Membrane Glycoproteins / Q000737:chemistry; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D015221:Potassium Channels / Q000235:genetics*; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014018:Tissue Distribution; D000098854:Kcnj10 Channel
C103861:KCNJ15 protein, human; D000098854:Kcnj10 Channel; D008562:Membrane Glycoproteins; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger