Multiple molecular mechanisms are involved in the activation of the kidney sodium-chloride cotransporter by hypokalemia.

Low potassium intake activates the kidney sodium-chloride cotransporter (NCC) whose phosphorylation and activity depend on the With-No-Lysine kinase 4 (WNK4) that is inhibited by chloride binding to its kinase domain. Low extracellular potassium activates NCC by decreasing intracellular chloride thereby promoting chloride dissociation from WNK4 where residue L319 of WNK4 participates in chloride coordination. Since the WNK4-L319F mutant is constitutively active and chloride-insensitive in vitro, we generated mice harboring this mutation that displayed slightly increased phosphorylated NCC and mild hyperkalemia when on a 129/sv genetic background. On a low potassium diet, upregulation of phosphorylated NCC was observed, suggesting that in addition to chloride sensing by WNK4, other mechanisms participate which may include modulation of WNK4 activity and degradation by phosphorylation of the RRxS motif in regulatory domains present in WNK4 and KLHL3, respectively. Increased levels of WNK4 and kidney-specific WNK1 and phospho-WNK4-RRxS were observed in wild-type and WNK4L319F/L319F mice on a low potassium diet. Decreased extracellular potassium promoted WNK4-RRxS phosphorylation in vitro and ex vivo as well. These effects might be secondary to intracellular chloride depletion, as reduction of intracellular chloride in HEK293 cells increased phospho-WNK4-RRxS. Phospho-WNK4-RRxS levels were increased in mice lacking the Kir5.1 potassium channel, which presumably have decreased distal convoluted tubule intracellular chloride. Similarly, phospho-KLHL3 was modulated by changes in intracellular chloride in HEK293 cells. Thus, our data suggest that multiple chloride-regulated mechanisms are responsible for NCC upregulation by low extracellular potassium.

Factors Associated with Development of Acute Kidney Injury After Liver Transplantation.

BACKGROUND: Early post-liver transplant (LT) acute kidney injury (AKI) has been associated with worse short-term and long-term outcomes, but the incidence and risk factors in our population are unknown. METHODS: We designed a prospective, singlecenter, longitudinal cohort study to determine the incidence of AKI during the immediate postoperative period of LT, and to identify the risk factors associated with AKI after LT. Pre-operative and intraoperative variables were analyzed to determine if there was any correlation with the development of post-operative AKI. RESULTS: Eighty-six patients were included in the final analysis; from them, 45 (52%) developed AKI in the following 30 days after LT. The presence of hepatic encephalopathy prior to LT was the factor most strongly associated with the development of AKI (Relative Risk 3.67, 95% Confidence Interval 1.08-8.95). Other factors associated with AKI development were male gender and a higher serum lactate during surgery. CONCLUSION: AKI was a frequent complication that significantly worsened the prognosis of LT recipients and was associated with an increased 30-day mortality rate. The presence of hepatic encephalopathy strongly predicted the development of severe AKI.