EAST/SeSAME syndrome mutations partially disrupt trafficking of homomeric Kir4.1 channels and produce non‐functional heteromeric Kir2.3/Kir4.1 channels

Abstract

Mutations in Kir4.1 cause renal salt and Mg wasting (EAST/ SeSAME syndrome, E/S) within the DCT. We have recently found that WT Kir4.1 co‐assembles and co‐localizes with Kir2.3 to produce heteromeric channels with properties similar to native channels in distal nephron. We previously reported that E/S Kir4.1 mutants disrupt Kir2.3 function, raising the possibility that E/S Kir4.1 mutants broadly disrupt the basolateral K+ conductance by dominant negative (DN) effects. Here we further investigate the mechanisms underlying the inhibitory effects of E/S mutants on WT Kir4.1 and Kir2.3 channels. By comparing current density to cell surface expression of external epitope tagged Kir2.3 or Kir4.1 channels, we found that inhibitory effects arise from disturbances in either trafficking or gating. Co‐expression of E/S mutant channels (R65P, C140R, R199X, R297C) with WT Kir4.1 resulted in a decreased current density (20–40%). The inhibitory effect of mutants R65P, C140R and R199X resulted from impaired surface expression while others affected channel gating. By contrast, five of the six mutants (not C140R) exerted a DN effect on Kir2.3 largely by altering channel gating. In summary, Kir4.1 E/S mutant channels affect gating and trafficking of heteromeric channels at the basolateral membrane of the distal nephron. Funded by NIH.