Secretory-Defect Distal Renal Tubular Acidosis Is Associated with Transporter Defect in H+-ATPase and Anion Exchanger-1

Abstract

Recent progress in molecular physiology has permitted us to understand pathophysiology of various channelopathies at a molecular level. The secretion of H⁺ from α-intercalated cells is mediated by apical plasma membrane H⁺-ATPase and basolateral plasma membrane anion exchanger-1 (AE1). Studies have demonstrated the lack of H⁺-ATPase immunostaining in the intercalated cells in a few patients with distal renal tubular acidosis (dRTA). Mutations in H⁺-ATPase and AE1 gene have recently been reported to cause dRTA. This study extends the investigation of the role of transporter defect in dRTA by using immunohistochemical methods. Eleven patients with hyperchloremic metabolic acidosis were diagnosed functionally to have secretory-defect dRTA: urine pH >5.5 during acidemia, normokalemia or hypokalemia, and urine-to-blood pCO₂ +-ATPase and AE1. For comparison, renal tissues from the patients who had no evidences of distal acidification defect by functional studies were used: four with glomerulopathy or tubulointerstitial nephritis (disease controls) and three from nephrectomized kidneys for renal cell carcinoma (normal controls). The H⁺-ATPase immunoreactivity in α-intercalated cells was almost absent in all of the 11 patients with secretory-defect dRTA. In addition, 7 of 11 patients with secretory-defect dRTA were accompanied by negative AE1 immunoreactivity. In both disease controls and normal controls, the immunoreactivity of H⁺-ATPase and AE1 was strong in α-intercalated cells. In conclusion, significant defect in acid-base transporters is the major cause of secretory-defect dRTA.