A Bartter's syndrome mutation of ROMK1 exerts dominant negative effects onK+ conductance

Mutations in the gene encoding the renal epithelial K+ channel ROMK1 (Kir 1 .1) is one of the causes for Bartter's syndrome, an autosomal recessive dis ease. It results in defective renal tubular transport in the thick ascendin g limb of the loop of Henle that leads to hypokalemic metabolic alkalosis a nd loss of salt. Two novel ROMK1 mutations, L220F/A156V, have been describe d recently in a compound heterozygote patient demonstrating typical manifes tations of Bartter's syndrome. Functional properties of these ROMK1 mutants were studied by coexpressing in Xenopus oocytes and by means of double ele ctrode voltage clamp experiments. When both ROMK1 mutants were coexpressed no K+ conductance could be detected. The same was found in oocytes expressi ng A156V-ROMK1 only or coexpressing wild type (wt) ROMK1 together with A156 V-ROMK1. In contrast, K+ conductances were indistinguishable from that of w t-ROMK1 when L220F-ROMK1 was expressed alone. Activation of protein kinase C signaling inhibited the conductance in both L220F-ROMK1 and wt-ROMK1 expr essing oocytes. These effects were not seen in A156V-ROMK1 expressing oocyt es. Because no further abnormalities in the properties or regulation of L22 0F-ROMK1 were detected, we conclude that A156V-ROMK1 has a dominant negativ e effect on L220F-ROMK1 thereby causing Bartter's syndrome type two in this patient. Copyright (C) 2000 S. Karger AG, Basel.