Details

Autor(en) / Beteiligte

• Shuck, M E
• Piser, T M
• Bock, J H
• Slightom, J L
• Lee, K S
• Bienkowski, M J

Titel

Cloning and Characterization of Two K+ Inward Rectifier (Kir) 1.1 Potassium Channel Homologs from Human Kidney (Kir1.2 and Kir1.3)

Ist Teil von

• The Journal of biological chemistry, 1997-01, Vol.272 (1), p.586-593

Ort / Verlag

United States: American Society for Biochemistry and Molecular Biology

Erscheinungsjahr

1997

Quelle

MEDLINE

Beschreibungen/Notizen

• 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 K ir 1.2 and K ir 1.3, which were derived from transcription of distinct human genes. K ir 1.2 represents the human homolog of the rat BIRK-10 sequence, whereas K ir 1.3 was unique compared with all available sequence data bases. The genes that encode K ir 1.2 and K ir 1.3 were mapped to human chromosomes 1 and 21, respectively. Both genes showed tissue-specific expression when analyzed by Northern blots. K ir 1.2 was only detected in brain ≫ kidney and was detected at high levels in all brain regions examined. K ir 1.3 was most readily detected in kidney and was also expressed in pancreas > lung. Comparative analysis of the predicted amino acid sequences for K ir 1.2 and K ir 1.3 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 K ir 1.1 and K ir 1.2 was not conserved in the K ir 1.3 sequence. Expression of the K ir 1.2 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 Ba 2+ and Cs + . K ir 1.2 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 IC 50 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, K ir 1.3 expression in Xenopus oocytes was not detectable despite the fact that the cRNA efficiently directed the synthesis of a polypeptide of the expected M r in an in vitro translation system. Co-expression of K ir 1.3 with either K ir 1.1 or K ir 1.2 reduced currents resulting from expression of these inward-rectifier subunits alone, consistent with a dominant negative influence on K ir 1.1 and K ir 1.2 expression.