Proceedings of The Physiological Society
University College London (2011) Proc Physiol Soc 24, C04 and PC04
Mirror-like SeSAME/EAST renal phenotype in mice lacking the pH-sensitive Kir5.1 (Kcnj16) K+ channel subunit
M. Paulais1, M. Keck1, S. Lourdel1, S. J. Tucker2, J. Teulon1
1. UMRS872 - ERL 7226, Paris, France. 2. Department of Physics, University of Oxford, Oxford, United Kingdom.
The heterotetrameric association of Kir4.1 and Kir5.1 subunits forms a 45 pS, inwardly-rectifying and pH-sensitive, K+ channel which underlies the major component of the basolateral membrane K+ conductance along the distal nephron (1,2,3). The functional importance of Kir4.1/Kir5.1 channel in renal ion transport has recently been highlighted by the identification of mutations in the human Kir4.1 gene which result in altered function of Kir4.1/Kir5.1 channel, a reduction in ion transport by the distal convoluted tubule (DCT) and ultimately in SeSAME/EAST syndrome, a complex disorder that includes salt wasting and hypokalaemic alkalosis (4,5). The extreme sensitivity of the Kir4.1/Kir5.1 channel to intracellular pH (pHi) is confered by the Kir5.1 subunit. Here, the role of the Kir5.1 subunit in renal function was investigated using mice with a targeted disruption of the Kir5.1 gene (Kcnj16). Mice were maintained in metabolic cages and urine was collected daily by non-invasive methods. Venous blood was taken from the retroorbital plexus of conscious animals. The Kir5.1-/- mice displayed hypercalciuria with hypokalaemic hyperchloremic metabolic acidosis (mean ± SE) (Kir5.1-/- : pHplasma = 7.19 ± 0.015, n = 10; Kir5.1+/+ : pHplasma = 7.35 ± 0.015, n = 11 ; P < 0.0001, Student t test). Addition of furosemide, an inhibitor of apical Na+/K+/2Cl- cotransporter in the thick ascending limb, to the powdered chow, or subcutaneous injection of amiloride, an inhibitor of apical Na+ channel (ENaC) in the aldosterone-sensitive distal nephron, revealed no significant alteration in ion transport by these structures in Kcnj16 deficient mice. By contrast, the increase in Na+ urine excretion observed in Kir5.1-/- mice (8.2 ± 3.8-fold, n = 12) in response to a short-term exposure to hydrochlorothiazide (HCTZ, i.p. injection), an inhibitor of ion transport in the DCT, was significantly higher than that observed in Kir5.1+/+ mice (2.9 ± 0.4-fold, n = 10; P < 0.05, Student t test), indicating an excessive salt absorption in DCT cells of Kir5.1-/- mice. Furthermore, a 4-day treatment with HCTZ added to the powdered chow normalized urinary excretion of sodium and calcium, and abolished acidosis in Kir5.1-/- mice. Single-channel patch clamp recording of K+ channels in the DCT basolateral membrane of Kir5.1+/+ and Kir5.1-/- mice revealed that Kcnj16 deletion led to an increased membrane K+ conductance (Kir5.1-/- : Po*g = 7.94 ± 0.62 pS, n = 10; Kir5.1+/+ : Po*g = 5.12 ± 1.12 pS, n = 7 ; P < 0.05, Student t test), due to the high and pH-insensitive open probability of the remaining homomeric Kir4.1 channels in Kir5.1-/- mice. In conclusion, disruption of Kcnj16 in mice induces an increase in ion transport activity in DCT cells, leading to a severe renal phenotype which, apart from hypokalaemia, is the opposite of the phenotype seen in SeSAME/EAST syndrome and highlights the important role played by Kir5.1 as a pH-sensitive regulator of renal function.
Where applicable, experiments conform with Society ethical requirements