The M338T mutation of Kir1.1b (ROMK2) channel caused mistargeting in MDCK cells

Bartter syndrome is renal tubular disorders that inhibit salt transport and increased renal salt wasting. Type II Bartter syndrome is caused by mutations in the KCNJ1 gene which encodes the inwardly rectifying ATP-sensitive potassium channel Kir1.1 (ROMK). They play a vital role in secretion of potassium into the tubule lumen. The effects of mutation at position 338 of ROMK2 (Kir1.1.b) was investigate. Site-directed mutagenesis was used to substitute of threonine for methionine at position 338 of ROMK2 (Kir1.1.b). M338T mutant ROMK2 expressed in oocytes of Xenopus laevis, and in a non-polarized mammalian cell line (MDCK). Two electrode voltage clamp and were used to measure oocyte ROMK-dependent currents. Confocal microscopy of EGFP-tagged ROMK2 determined express and distribution of these channels in MDCK cells. The M338T mutant ROMK2 protein expressed in oocytes was functionally identical to wild type. Its cellular distribution was different in polarized and non-polarized MDCK cells. The M338T mutation is altered residue interactions within the carboxyl terminus of ROMK2 channels. Thus mistargeting of ROMK2 in vivo reduces the driving force for potassium secretion in the TAL and reduces salt reabsorption by this nephron segment.