Mutations of the KCNJ10 (Kir4.1) K(+) channel underlie autosomal recessive 
epilepsy, ataxia, sensorineural deafness, and (a salt-wasting) renal tubulopathy 
(EAST) syndrome. We investigated the localization of KCNJ10 and the homologous 
KCNJ16 in kidney and the functional consequences of KCNJ10 mutations found in 
our patients with EAST syndrome. Kcnj10 and Kcnj16 were found in the basolateral 
membrane of mouse distal convoluted tubules, connecting tubules, and cortical 
collecting ducts. In the human kidney, KCNJ10 staining was additionally observed 
in the basolateral membrane of the cortical thick ascending limb of Henle's 
loop. EM of distal tubular cells of a patient with EAST syndrome showed reduced 
basal infoldings in this nephron segment, which likely reflects the 
morphological consequences of the impaired salt reabsorption capacity. When 
expressed in CHO and HEK293 cells, the KCNJ10 mutations R65P, G77R, and R175Q 
caused a marked impairment of channel function. R199X showed complete loss of 
function. Single-channel analysis revealed a strongly reduced mean open time. 
Qualitatively similar results were obtained with coexpression of KCNJ10/KCNJ16, 
suggesting a dominance of KCNJ10 function in native renal KCNJ10/KCNJ16 
heteromers. The decrease in the current of R65P and R175Q was mainly caused by a 
remarkable shift of pH sensitivity to the alkaline range. In summary, EAST 
mutations of KCNJ10 lead to impaired channel function and structural changes in 
distal convoluted tubules. Intriguingly, the metabolic alkalosis present in 
patients carrying the R65P mutation possibly improves residual function of 
KCNJ10, which shows higher activity at alkaline pH.