Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 108 (25), 10361-6

Renal Phenotype in Mice Lacking the Kir5.1 (Kcnj16) K+ Channel Subunit Contrasts With That Observed in SeSAME/EAST Syndrome

Affiliations

Renal Phenotype in Mice Lacking the Kir5.1 (Kcnj16) K+ Channel Subunit Contrasts With That Observed in SeSAME/EAST Syndrome

Marc Paulais et al. Proc Natl Acad Sci U S A.

Abstract

The heteromeric inwardly rectifying Kir4.1/Kir5.1 K(+) channel underlies the basolateral K(+) conductance in the distal nephron and is extremely sensitive to inhibition by intracellular pH. The functional importance of Kir4.1/Kir5.1 in renal ion transport has recently been highlighted by mutations in the human Kir4.1 gene (KCNJ10) that result in seizures, sensorineural deafness, ataxia, mental retardation, and electrolyte imbalance (SeSAME)/epilepsy, ataxia, sensorineural deafness, and renal tubulopathy (EAST) syndrome, a complex disorder that includes salt wasting and hypokalemic alkalosis. Here, we investigated the role of the Kir5.1 subunit in mice with a targeted disruption of the Kir5.1 gene (Kcnj16). The Kir5.1(-/-) mice displayed hypokalemic, hyperchloremic metabolic acidosis with hypercalciuria. The short-term responses to hydrochlorothiazide, an inhibitor of ion transport in the distal convoluted tubule (DCT), were also exaggerated, indicating excessive renal Na(+) absorption in this segment. Furthermore, chronic treatment with hydrochlorothiazide normalized urinary excretion of Na(+) and Ca(2+), and abolished acidosis in Kir5.1(-/-) mice. Finally, in contrast to WT mice, electrophysiological recording of K(+) channels in the DCT basolateral membrane of Kir5.1(-/-) mice revealed that, even though Kir5.1 is absent, there is an increased K(+) conductance caused by the decreased pH sensitivity of the remaining homomeric Kir4.1 channels. In conclusion, disruption of Kcnj16 induces a severe renal phenotype that, apart from hypokalemia, is the opposite of the phenotype seen in SeSAME/EAST syndrome. These results highlight the important role that Kir5.1 plays as a pH-sensitive regulator of salt transport in the DCT, and the implication of these results for the correct genetic diagnosis of renal tubulopathies is discussed.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Urine-concentrating ability of Kir5.1+/+ and Kir5.1−/− mice. Daily diuresis (A) and urine osmolality (B) of Kir5.1+/+ (□) and Kir5.1−/− (■) mice maintained in metabolic cages were first measured while the mice had free access to demineralized water (+H2O), and then after a 24-h period of water deprivation (−H2O). Weight loss induced by water deprivation averaged 7% and 9% for Kir5.1+/+ and Kir5.1−/− mice, respectively. Water deprivation tests showed that both groups of mice had similar urine-concentrating abilities. Values are mean values for 10 Kir5.1+/+ and eight Kir5.1−/− mice. Error bars represent SEM when larger than symbols. *P < 0.05, Kir5.1−/− versus Kir5.1+/+ mice.
Fig. 2.
Fig. 2.
Effects of furosemide and amiloride. Kir5.1+/+ (□) and Kir5.1−/− (■) mice maintained in metabolic cages were subjected to furosemide (A) or amiloride (B) treatment for 6 h. Urinary Na+ and Ca2+ excretion were measured before (−Furo) and after (+Furo) furosemide treatment, and urinary Na+ and K+ excretion were measured before (−Amilo) and after (+Amilo) amiloride treatments. Values are means for 12 (A) or 10 (B) Kir5.1+/+ mice and 12 (A) or eight (B) Kir5.1−/− mice. Error bars represent SEM when larger than symbols. All diuretic-induced responses were statistically significant (P < 0.05).
Fig. 3.
Fig. 3.
Short- and long-term effects of HCTZ. (A) Urinary Na+ and Ca2+ excretion of Kir5.1+/+ (□) and Kir5.1−/− (■) mice were measured before (−HCTZ) and after 6 h of treatment (+HCTZ). (B) Urinary Na+ (Left) and Ca2+ (Right) were measured in Kir5.1+/+ and Kir5.1−/− mice before (white bars) and after (black bars) a 4-d HCTZ treatment. Values are means ± SEM for 10 (A) or 12 (B) Kir5.1+/+ mice and nine (A) or 12 (B) Kir5.1−/− mice. *P < 0.05 versus control; NS, no significant difference at P < 0.05.
Fig. 4.
Fig. 4.
Analysis of channel currents in the basolateral membrane of DCT tubules. (A) Left: Current (i)–voltage (Vm) relationships for the K+ channels detected in the DCTs of Kir5.1+/+ (□) and Kir5.1−/− (■) mice in the cell-attached configuration. Tubules were bathed with physiological saline solution, and the pipette contained 145 mM KCl. Values are means of 15 patches from three Kir5.1+/+ mice and 17 patches from four Kir5.1−/− mice. Error bars represent SEM when larger than symbols. Right: Current traces recorded in the cell-attached mode at the designed potentials for the two groups. “C” indicates the closed current level. (B) Diagrams for the channel Po and the averaged unit conductance, as defined by the product of individual measurements of Po and g, for the two groups of mice. Values are means of the numbers patches in Kir5.1+/+ and Kir5.1−/− mice given in A. Error bars represent SEM; *P < 0.001. (C) Sensitivity to pHi as measured in inside-out patches at +60 to 80 mV for Kir5.1+/+ (□) and Kir5.1−/− (■) mouse DCTs. Each point is the mean of eight measurements in Kir5.1+/+ mice and nine measurements in Kir5.1−/− mice. Error bars represent SEM when larger than symbols.
Fig. 5.
Fig. 5.
A cellular model for enhanced salt transport in DCT caused by deletion of Kcnj16. (A) Basolateral Kir4.1/Kir5.1 channels recycle K+ entering the cell via the Na+/K+ ATPase. The continuous functioning of the Na+/K+ ATPase maintains a chemical gradient favorable to Na+ and Cl apical entry via the thiazide-sensitive electroneutral NCC. Kir4.1/Kir5.1 channels also maintain a negative basolateral membrane potential difference, thus providing a favorable electrochemical gradient to basolateral Cl exit through ClC-Kb Cl channels. Changes in pHi are sensed by Kir4.1/Kir5.1 channels and affect basolateral K+ conductance, thereby modulating salt reabsorption by DCT cells. (B) Kcnj16 deletion induces the formation of pHi-insensitive and constitutively highly active basolateral homomeric Kir4.1 channels. The resulting increase in basolateral K+ conductance is expected to enhance basolateral Cl exit and Na+-K+ ATPase and NCC transport activities and thus to up-regulate overall salt reabsorption by DCT.

Similar articles

See all similar articles

Cited by 37 PubMed Central articles

See all "Cited by" articles

Publication types

MeSH terms

Feedback