Renal phenotype in mice lacking the Kir5.1 (Kcnj16) K+ channel subunit contrasts with that observed in SeSAME/EAST syndrome Marc Paulaisa,b,1, May Bloch-Faurea,b, Nicolas Picarda,b, Thibaut Jacquesb,c, Suresh Krishna Ramakrishnana,b, Mathilde Kecka,b, Fabien Soheta,b, Dominique Eladaria,b,c,d, Pascal Houilliera,b,c,d, Stéphane Lourdela,b, Jacques Teulona,b, and Stephen J. Tuckere aUniversité Pierre et Marie Curie Paris 6, Université Paris 5, and Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche en Santé 872, 75006 Paris, France; bCentre National de la Recherche Scientifique, Équipes de Recherche Labellisées 7226, Genomics Physiology, and Renal Physiopathology Laboratory, Centre de Recherche des Cordeliers, 75270 Paris 6, France; cFaculty of Medicine, Université Paris–Descartes, 75006 Paris, France; dAssistance Publique–Hôpitaux de Paris, Hôpital Européen Georges Pompidou, 75015 Paris, France; and eClarendon Laboratory and Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom Edited by Maurice B. Burg, National Heart, Lung, and Blood Institute, Bethesda, MD, and approved May 9, 2011 (received for review January 31, 2011) The heteromeric inwardly rectifying Kir4.1/Kir5.1 K+ channel underlies encodes the Kir4.1 subunit, underlie SeSAME/EAST syndrome, the basolateral K+ conductance in the distal nephron and is extremely a rare disorder in which patients experience neurological and sensitive to inhibition by intracellular pH. The functional importance renal symptoms (11, 12). In the kidney, it is thought that these of Kir4.1/Kir5.1 in renal ion transport has recently been highlighted by loss-of-function mutations in Kir4.1 impair the function of het- mutations in the human Kir4.1 gene (KCNJ10) that result in seizures, eromeric Kir4.1/Kir5.1 channels (13, 14), thereby dramatically sensorineural deafness, ataxia, mental retardation, and electrolyte impairing salt reuptake from the DCT, and increasing down- imbalance (SeSAME)/epilepsy, ataxia, sensorineural deafness, and re- stream K+ and H+ secretion. This results in a Gitelman-like nal tubulopathy (EAST) syndrome, a complex disorder that includes syndrome, characterized by salt wasting, hypocalciuria, hypo- salt wasting and hypokalemic alkalosis. Here, we investigated the role magnesaemia, and hypokalemic metabolic alkalosis (11, 12, 15). of the Kir5.1 subunit in mice with a targeted disruption of the Kir5.1 The basolateral location of Kir4.1/Kir5.1 channels obviously −/− gene (Kcnj16). The Kir5.1 mice displayed hypokalemic, hyper- suggests a role for these channels in maintenance of the baso- chloremic metabolic acidosis with hypercalciuria. The short-term lateral membrane potential, and in the “recycling” across the responses to hydrochlorothiazide, an inhibitor of ion transport in basolateral membrane of any K+ that enters the cell via the the distal convoluted tubule (DCT), were also exaggerated, indicating basolateral Na+/K+ ATPase. The recycling of K+ is a crucial step excessive renal Na+ absorption in this segment. Furthermore, chronic for sustained transepithelial Na+ reabsorption. However, in the treatment with hydrochlorothiazide normalized urinary excretion of DCT of patients with seizures, sensorineural deafness, ataxia, Na+ and Ca2+, and abolished acidosis in Kir5.1−/− mice. Finally, in con- mental retardation, and electrolyte imbalance (SeSAME)/epilepsy, trast to WT mice, electrophysiological recording of K+ channels in the ataxia, sensorineural deafness, and renal tubulopathy (EAST) −/− DCT basolateral membrane of Kir5.1 mice revealed that, even syndrome, this K+ recycling seems to be altered. though Kir5.1 is absent, there is an increased K+ conductance caused The expression of Kir5.1 alone does not produce detectable by the decreased pH sensitivity of the remaining homomeric Kir4.1 K+ currents in most recombinant expression systems (16). In- channels. In conclusion, disruption of Kcnj16 induces a severe renal stead, this “silent” subunit appears to heteromultimerize with phenotype that, apart from hypokalemia, is the opposite of the phe- Kir4.1 to produce novel Kir4.1/Kir5.1 channels (17–19) that have notype seen in SeSAME/EAST syndrome. These results highlight the an extreme sensitivity to intracellular pH (pHi) within the physi- important role that Kir5.1 plays as a pH-sensitive regulator of salt ological range (i.e., pKa of 7.4) (18, 20, 21). By contrast, homo- PHYSIOLOGY transport in the DCT, and the implication of these results for the meric Kir4.1 channels are only mildly sensitive to pHi (pKa, 6.0). correct genetic diagnosis of renal tubulopathies is discussed. This therefore raises the important question of how Kir5.1 con- tributes to renal ion transport and the role of these highly pH- kidney | homeostasis | acid–base balance sensitive Kir4.1/Kir5.1 channels in this process. The present study addresses this issue by using a recently + channels play critical roles in renal tubular transport created strain of mice in which the Kir5.1(Kcnj16) gene has been + deleted (22). We show that deletion of this subunit results in a K functions directly by providing a secretory pathway for K + or indirectly by controlling membrane voltage and K+ recycling pHi-insensitive, highly active K conductance in the DCT baso- across the plasma membrane (1). Recent genetic and functional lateral membrane, and a severe renal phenotype characterized by studies have shown that loss of renal K+ channel activity not only hypokalemic metabolic acidosis with hypercalciuria. Thus, instead has an impact on K+ balance, but also affects other ion transport of producing an effect similar to SeSAME/EAST syndrome mutations in Kir4.1, inactivation of Kir5.1 reduces the pH sen- systems and the regulation of the acid–base balance. For in- i sitivity of the DCT basolateral K+ conductance and produces a stance, it has been clearly established that inherited mutations of mirror-image phenotype to SeSAME/EAST syndrome by increasing the human KCNJ1 gene underlie type II Bartter syndrome, a + the mean basolateral K conductance in the distal nephron. severe disorder involving renal salt wasting and hypokalemic metabolic alkalosis (2). Likewise, inactivation of the Kcnk5 gene encoding the acid- and volume-sensitive TASK2 K+ channel − Author contributions: M.P. and J.T. designed research; M.P., M.B.-F., N.P., T.J., S.K.R., M.K., induces renal HCO3 loss and metabolic acidosis in mice (3). F.S., P.H., S.L., and J.T. performed research; M.P., N.P., T.J., S.L., and J.T. analyzed data; and The cortical thick ascending limb (4, 5), distal convoluted tu- M.P., D.E., J.T., and S.J.T. wrote the paper. bule (DCT) (6, 7), and cortical collecting duct (CCD) principal The authors declare no conflict of interest. + cells (8, 9) are endowed with K channels displaying properties This article is a PNAS Direct Submission. + identical to inwardly rectifying heteromeric Kir4.1/Kir5.1 K 1To whom correspondence should be addressed. E-mail: [email protected]. channels (10). Recent studies have reported that rare homozy- This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. gous missense mutations of the human KCNJ10 gene, which 1073/pnas.1101400108/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1101400108 PNAS | June 21, 2011 | vol. 108 | no. 25 | 10361–10366 Downloaded by guest on October 1, 2021 Results −/− Clinical Parameters of Kir5.1 Mice. There was no obvious dif- ference in the survival or gross physical appearance between − − Kir5.1+/+ and Kir5.1 / mice maintained on a control diet, except − − for an approximately 15% lower body weight of the Kir5.1 / − − mice (P < 0.0001; Table 1). Kir5.1 / mice were slightly poly- dipsic, and exhibited polyuria and correspondingly lower urine osmolality. However, both groups of mice adapted normally to 24 h water restriction (Fig. 1), indicating that the urine- − − concentrating ability of Kir5.1 / mice is not impaired. Further- − − more, the hematocrit level of Kir5.1 / mice was not increased − − (45.7 ± 1.42% vs. 45.5 ± 1.13% for Kir5.1+/+ and Kir5.1 / mice, respectively; P = 0.4), indicating the absence of dehydration. Fig. 1. Urine-concentrating ability of Kir5.1+/+ and Kir5.1−/− mice. Daily di- uresis (A) and urine osmolality (B)ofKir5.1+/+ (□) and Kir5.1−/− (■) mice −/− Kir5.1 Mice Display Metabolic Acidosis and Hypokalemia. Blood maintained in metabolic cages were first measured while the mice had −/− and plasma analyses revealed that Kir5.1 mice had metabolic free access to demineralized water (+H2O), and then after a 24-h period of water deprivation (−H2O). Weight loss induced by water deprivation aver- hyperchloremic acidosis (Table 1). However, despite this acidosis, − − + aged 7% and 9% for Kir5.1+/+ and Kir5.1 / mice, respectively. Water depri- urinary NH4 excretion was not increased (81 ± 3.5 mmol/mmol −/− vation tests showed that both groups of mice had similar urine-concentrating creatinine in 10 Kir5.1 mice vs. 99 ± 5.2 mmol/mmol creatinine in +/+ −/− +/+ abilities. Values are mean values for 10 Kir5.1 and eight Kir5.1 mice. fi − − 11 Kir5.1 mice). Also, glomerular ltration rates were similar in Error bars represent SEM when larger than symbols. *P < 0.05, Kir5.1 / versus +/+ −/− Kir5.1 mice (308 ± 43 μL/min; n = 11) and Kir5.1 mice (272 Kir5.1+/+ mice. ± 35 μL/min; n =7;P = 0.54), indicating the absence of chronic − − renal failure. Our data therefore clearly show that Kir5.1 / mice have renal tubular acidosis. However, this may also be associated No Alteration in the Responses to Furosemide and Amiloride in − − −/− with a respiratory component because the Kir5.1 / mice do not Kir5.1 Mice. Expression of Kir5.1 is also seen in the TAL and display the expected compensatory decrease in blood PCO2 (Table DCT cells, as well as in CCD principal cells, where it coassem- 1), an effect that would be consistent with the respiratory phe- bles with Kir4.1 to form Kir4.1/Kir5.1 channels in the basolateral notype recently reported in these mice (22).