Kidney Week

Abstract: FR-OR126

Expression, Localization, and Role of Slc4a8 (NDCBE) in Acid Base Transport in Kidney Tubules

Session Information

• Urinary Concentration and Acidification
  November 03, 2017 | Location: Room 290, Morial Convention Center
  Abstract Time: 04:42 PM - 04:54 PM

Category: Fluid, Electrolytes, and Acid-Base

• 701 Acid-Base: Basic

Authors

• Xu, Jie, University of Cincinnati, Cincinnati, Ohio, United States

Jie Xu,

• Barone, Sharon L., University of Cincinnati, Cincinnati, Ohio, United States

Sharon L. Barone,

• Brooks, Marybeth, University of Cincinnati, Cincinnati, Ohio, United States

Marybeth Brooks,

• Soleimani, Manoocher, University of Cincinnati, Cincinnati, Ohio, United States

Manoocher Soleimani, MD

Background

The sodium-dependent bicarbonate transporter Slc4a8, also known as NDCBE, mediates the cotransport of sodium and bicarbonate in exchange for chloride (Na-dependent Cl^-/HCO₃^- exchanger). NDCBE is abundantly detected in the brain, with very low expression levels in the kidney. The cell distribution, subcellular localization and role of NDCBE in acid/base and electrolyte homeostasis in the kidney have been the subject of conflicting reports. There are no localization studies (such as immunolabeling and/or in situ hybridization) and no functional studies to pinpoint the location and demonstrate the function of NDCBE in the kidney.

Methods

Molecular techniques including RT-PCR, Northern Hybridization and in situ hybridization were employed in kidney sections and tagged epitopes were used to examine the membrane localization of NDCBE in transfected polarized kidney epithelium. Crispr/Cas9 approach was used to generate and examine NDCBE KO mice.

Results

Zonal distribution (cortex, outer medulla and inner medulla) studies by northern hybridization and RT-PCR and in situ hybridization experiments using FISH (Fluorescence In Situ Hybridization) showed very little to no expression for NDCBE in the cortex or in cortical collecting ducts (CCD). NDCBE was predominantly detected in the kidney medulla with significant expression in medullary collecting ducts. NDCBE was targeted to the basolateral membrane of MDCK cells when grown in hypertonic medium, a physiologic environment for cells in medullary collecting duct. NDCBE deficient mice show no salt, bicarbonate or fluid wasting phenotype under baseline condition, and their urine pH remained comparable to wild type mice in response to bicarbonate loading or salt restriction. Expression levels of pendrin and NCC were comparable in kidney cortices of NDCBE KO and wild type mice.

Conclusion

Slc4a8 (NDCBE) is predominantly detected in mouse medullary collecting duct, is targeted to the basolateral membrane, shows increased activity in hypertonic environment and its deletion does not cause any noticeable acid base perturbation either under baseline conditions or in response to bicarbonate loading or salt restriction.

Funding

• Veterans Affairs Support