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A cDNA clone encoding an inwardly-rectifying K-channel (BIR1) was isolated from insulinoma cells. The predicted amino acid sequence shares 72% identity with the cardiac ATP-sensitive K-channel rcKATP (KATP-1;[6]). The mRNA is expressed in the brain and insulinoma cells. Heterologous expression in Xenopus oocytes produced currents which were K(+)-selective, time-independent and showed inward rectification. The currents were blocked by external barium and caesium, but insensitive to tolbutamide and diazoxide. In inside-out patches, channel activity was not blocked by 1 mM internal ATP. The sequence homology with KATP-1 suggests that BIR1 is a subunit of a brain and beta-cell KATP channel. However, pharmacological differences and the lack of ATP-sensitivity, suggest that if, this is the case, heterologous subunits must exert strong modulatory influences on the native channel.

Original publication




Journal article



Publication Date





61 - 66


Amino Acid Sequence, Animals, Base Sequence, Brain, Cloning, Molecular, DNA, Complementary, Humans, Insulinoma, Islets of Langerhans, Molecular Sequence Data, Patch-Clamp Techniques, Potassium Channels, Rats, Sequence Alignment, Tumor Cells, Cultured, Xenopus