Effect of extracellular potassium on the activity of distal renal tubule in mice / 上海交通大学学报（医学版）

Objective: To investigate the effect of extracellular potassium (K+) concentration on the activities of sodium chloride co-transporter (NCC) and large conductance Ca2+-activated K+ channel (BK) in distal renal tubule of mice. Methods: Six specific pathogen free (SPF) C57BL/6 mice aged 8 to 10 weeks were sacrificed,and the kidney slices were made with previously reported method. Then,these slices were incubated randomly in normal K+,high K+,BaCl2 and RbCl solutions,respectively. The abundance and phosphorylation level of NCC in kidney slices at different K+ concentrations and different time courses were detected by Western blotting. The overall and membrane expressions of BK in kidney slices were also detected after incubation with different K+ solutions for 2 h. Results: Compared with normal K+ solution,NCC phosphorylation level was significantly decreased after incubation with high K+ solution for 5,15,30 min (all P<0.05),and NCC phosphorylation level was also decreased after intervention with K+ channel inhibitor Ba2+ or Rb+ (both P<0.05). After the treatment with high K+ solution for 2 h,neither the overall cell expression of BKα subunit and β4 subunit,nor membrane expression of BKα subunit was found significant changes compared with normal K+ incubation. Conclusion: High K+ can directly down-regulate NCC phosphorylation level,which may be preparation for kaliuresis of the downstream tubule of distal convoluted tubule.

Absence of intact thiazide-sensitive sodium-chloride cotransporter in the renal tissue of a Gitelman's syndrome patient / 대한내과학회지

BACKGROUND: Gitelman's syndrome is an autosomal recessive renal tubular disorder characterized by hypokalemic metabolic alkalosis, hypomagnesemia, and hypocalciuria. It is known to be caused by a mutation of SLC12A3 gene coding the sodium-chloride cotransporter (NCCT) in the distal tubule. The defect of NCCT in human renal tissues has not been investigated, and we tested whether the defect of NCCT can be detected in renal tissue of a patient with Gitelman's syndrome by using immunohistochemistry. METHODS: In an adult patient with Gitelman's syndrome, blood and urine samples were collected for measurement of biochemical parameters. Renal clearance study and gene analysis were performed. Immunohistochemistry was performed on the renal tissue of the patient using a rabbit polyclonal antibody directed against a synthetic peptide corresponding to a portion in the amino terminal tail for human NCCT. Normal human renal tissues from surgical nephrectomy due to renal cell carcinoma and renal biopsy tissues from patients with glomerulonephritis but without any electrolyte disturbance were used as controls. RESULTS: The patient had hypokalemic metabolic alkalosis, hypocalciuria and hypomagnesemia. Renal clearance study revealed a decrease in distal fractional chloride reabsorption after the administration of furosemide. SLC12A3 gene mutation (S967F) was found by direct sequencing method. Immunohistochemistry showed the absence of NCCT staining in the renal tissue of the patient. On the other hand, the immunostaining of other transporters was all positive in renal tissues from both Gitelman's syndrome patients and controls. CONCLUSIONS: We report the absence of intact NCCT in the renal tissue of a Gitelman's syndrome patient.