Mutations in all four known KCNQ potassium channel alpha-subunit genes lead to human diseases. KCNQ1 (KvLQT1) interacts with the beta-subunit KCNE1 (IsK, minK) to form the slow, depolarization-activated potassium current I(Ks) that is affected in some forms of cardiac arrhythmia. Here we show that the novel beta-subunit KCNE3 markedly changes KCNQ1 properties to yield currents that are nearly instantaneous and depend linearly on voltage. It also suppresses the currents of KCNQ4 and HERG potassium channels. In the intestine, KCNQ1 and KCNE3 messenger RNAs colocalized in crypt cells. This localization and the pharmacology, voltage-dependence and stimulation by cyclic AMP of KCNQ1/KCNE3 currents indicate that these proteins may assemble to form the potassium channel that is important for cyclic AMP-stimulated intestinal chloride secretion and that is involved in secretory diarrhoea and cystic fibrosis.

BACKGROUND Five children from two consanguineous families presented with epilepsy beginning in infancy and severe ataxia, moderate sensorineural deafness, and a renal salt-losing tubulopathy with normotensive hypokalemic metabolic alkalosis. We investigated the genetic basis of this autosomal recessive disease, which we call the EAST syndrome (the presence of epilepsy, ataxia, sensorineural deafness, and tubulopathy). METHODS Whole-genome linkage analysis was performed in the four affected children in one of the families. Newly identified mutations in a potassium-channel gene were evaluated with the use of a heterologous expression system. Protein expression and function were further investigated in genetically modified mice. RESULTS Linkage analysis identified a single significant locus on chromosome 1q23.2 with a lod score of 4.98. This region contained the KCNJ10 gene, which encodes a potassium channel expressed in the brain, inner ear, and kidney. Sequencing of this candidate gene revealed homozygous missense mutations in affected persons in both families. These mutations, when expressed heterologously in xenopus oocytes, caused significant and specific decreases in potassium currents. Mice with Kcnj10 deletions became dehydrated, with definitive evidence of renal salt wasting. CONCLUSIONS Mutations in KCNJ10 cause a specific disorder, consisting of epilepsy, ataxia, sensorineural deafness, and tubulopathy. Our findings indicate that KCNJ10 plays a major role in renal salt handling and, hence, possibly also in blood-pressure maintenance and its regulation.

Primary aldosteronism is the most prevalent form of secondary hypertension. To explore molecular mechanisms of autonomous aldosterone secretion, we performed exome sequencing of aldosterone-producing adenomas (APAs). We identified somatic hotspot mutations in the ATP1A1 (encoding an Na(+)/K(+) ATPase α subunit) and ATP2B3 (encoding a Ca(2+) ATPase) genes in three and two of the nine APAs, respectively. These ATPases are expressed in adrenal cells and control sodium, potassium and calcium ion homeostasis. Functional in vitro studies of ATP1A1 mutants showed loss of pump activity and strongly reduced affinity for potassium. Electrophysiological ex vivo studies on primary adrenal adenoma cells provided further evidence for inappropriate depolarization of cells with ATPase alterations. In a collection of 308 APAs, we found 16 (5.2%) somatic mutations in ATP1A1 and 5 (1.6%) in ATP2B3. Mutation-positive cases showed male dominance, increased plasma aldosterone concentrations and lower potassium concentrations compared with mutation-negative cases. In summary, dominant somatic alterations in two members of the ATPase gene family result in autonomous aldosterone secretion.

Mineralocorticoid receptor (MR)-deficient mice were generated by gene targeting. These animals had a normal prenatal development. During the first week of life, MR-deficient (؊͞؊) mice developed symptoms of pseudohypoaldosteronism. They finally lost weight and eventually died at around day 10 after birth from dehydration by renal sodium and water loss. At day 8, ؊͞؊ mice showed hyperkalemia, hyponatremia, and a strong increase in renin, angiotensin II, and aldosterone plasma concentrations. Methods were established to measure renal clearance and colonic transepithelial Na ؉ reabsorption in 8-day-old mice in vivo. The fractional renal Na ؉ excretion was elevated >8-fold. The glomerular filtration rate in ؊͞؊ mice was not different from controls. The effect of amiloride on renal Na ؉ excretion and colonic transepithelial voltage reflects the function of amiloide-sensitive epithelial Na ؉ channels (ENaC). In ؊͞؊ mice, it was reduced to 24% in the kidney and to 16% in the colon. There was, however, still significant residual ENaC-mediated Na ؉ reabsorption in both epithelia. RNase protection analysis of the subunits of ENaC and (Na ؉ ؉ K ؉ )-ATPase did not reveal a decrease in ؊͞؊ mice. The present data indicate that MR-deficient neonates die because they are not able to compensate renal Na ؉ loss. Regulation of Na ؉ reabsorption via MR is not achieved by transcriptional control of ENaC and (Na ؉ ؉ K ؉ )-ATPase in RNA abundance but by transcriptional control of other as yet unidentified genes. MR knockout mice will be a suitable tool for the search of these genes.