Single amino acid residue influences the distribution pattern of an inwardly rectifying potassium channel in polarized cells

We used immunohistochemistry to identify the localization of the inwardly rectifying potassium channels K-ir 2.1 and its mutant K-ir 2.1 M84K, and P2X(2) receptors heterologously expressed in Xenopus oocytes, opossum kidney (OK) cells and NG108-15 cells. Kir 2.1 wild-type channels were unevenly distributed over the surface of the oocytes and the density was higher at the vegetal pole than at the animal pole. In OK cells the protein was detected at the basolateral membrane, and in NG108-15 cells the protein was found in the soma of the cells and in long thick outgrowing neurites. In contrast, mutant Kir 2.1 M84K channels were evenly distributed over the membrane of the oocytes, whereas in OK cells the protein was only detected at the tips of the brush border. In NG108-15 cells the protein was found in the soma of the cells and in all growing neurites. The density of P2X(2) was higher at the animal pole of the oocytes and was restricted to the tips of the brush border in OK cells. In NG108-15 cells the protein was restricted to thinner outgrowing structures and the soma of the cells. We conclude that the exchange of a single amino acid residue in the N-terminus of K-ir 2.1 changes the distribution pattern in all of the cell types studied. Furthermore, we were able to show that another ion channel sharing the same topology with inwardly rectifying potassium channels showed a different distribution pattern in these cell types.