Molecular evidence for a role for K⁺-Cl⁻ cotransporters in the kidney

Abstract

K+-Cl− cotransporter (KCC) isoforms 3 (KCC3) and 4 (KCC4) are expressed at the basolateral membrane of proximal convoluted tubule cells, and KCC4 is present in the basolateral membrane of the thick ascending loop of Henle's limb and α-intercalated cells of the collecting duct. Little is known, however, about the physiological roles of these transporters in the kidney. We evaluated KCC3 and KCC4 mRNA and protein expression levels and intrarenal distribution in male Wistar rats or C57 mice under five experimental conditions: hyperglycemia after a single dose of streptozotocin, a low-salt diet, metabolic acidosis induced by ammonium chloride in drinking water, and low- or high-K+ diets. Both KCC3 mRNA and protein expression were increased during hyperglycemia in the renal cortex and at the basolateral membrane of proximal tubule cells but not with a low-salt diet or acidosis. In contrast, KCC4 protein expression was increased by a low-sodium diet in the whole kidney and by metabolic acidosis in the renal outer medulla, specifically at the basolateral membrane of α-intercalated cells. The increased protein expression of KCC4 by a low-salt diet was also observed in WNK4 knockout mice, suggesting that upregulation of KCC4 in these circumstances is not WNK4 dependent. No change in KCC3 or KCC4 protein expression was observed under low- or high-K+ diets. Our data are consistent with a role for KCC3 in the proximal tubule glucose reabsorption mechanism and for KCC4 in salt reabsorption of the thick ascending loop of Henle's loop and acid secretion of the collecting duct.

Physical and Functional Links between Anion Exchanger-1 and Sodium Pump

“…Acidified animals (n=6) developed a compensated metabolic acidosis, with blood pH and pCO 2 concentrations remaining similar compared with controls, which is consistent with a previous report. 59 …”

With no lysine L-WNK1 isoforms are negative regulators of the K+-Cl− cotransporters

“…KCC1 is considered a housekeeping isoform due to its ubiquitous expression pattern (32), while KCC4 is expressed in several tissues with a strong presence in the heart and kidney (35,42). KCC3 is expressed in multiple tissues with particularly abundant transcripts in heart, muscle, kidney, brain, and placenta (22,42,48).…”

“…Erythroid function and differentiation (30), cancer cell growth and invasiveness (8,57,58), arterial blood pressure regulation (54), and neuronal excitability (23,33,53) are some of the important roles of these membrane proteins. At the renal level, KCC3 is located in the basolateral membranes of the proximal tubules (PT) (40), while KCC4 is expressed in proximal tubules, in the thick ascending limb of Henle's loop (TALH) (35), and in ␣-intercalated cells of the collecting duct (CD) (6,35). In these zones of the nephron, KCC3 and KCC4 are involved in processes such as glucose and salt reabsorption and acid-base homeostasis (6,35).…”

“…At the renal level, KCC3 is located in the basolateral membranes of the proximal tubules (PT) (40), while KCC4 is expressed in proximal tubules, in the thick ascending limb of Henle's loop (TALH) (35), and in ␣-intercalated cells of the collecting duct (CD) (6,35). In these zones of the nephron, KCC3 and KCC4 are involved in processes such as glucose and salt reabsorption and acid-base homeostasis (6,35). It is known that KCCs are activated due to an increase in [Cl Ϫ ] i or by cell swelling (39,40,60).…”

Underdominant KCC3b R31I association with blood sodium concentration in domestic sheep suggests role in oligomer function

“…Two KCC3 isoforms differ by alternate promoters and first coding exons 3 : KCC3a is widely expressed and KCC3b is highly expressed in kidney proximal convoluted tubule 4 . We genotyped KCC3 and KCC1 amino acid substitutions using Taqman assays (Table S1) in 307 Suffolk, Rambouillet, Polypay and Columbia sheep.…”