Thick ascending limb claudins are altered to increase calciuria and magnesiuria in metabolic acidosis.

Abstract

Urinary calcium and magnesium wasting is a characteristic feature of metabolic acidosis, and this study focused on the role of the thick ascending limb of Henle's loop in metabolic acidosis-induced hypercalciuria and hypermagnesiuria because thick ascending limb is an important site of paracellular calcium and magnesium reabsorption. Male Sprague-Dawley rats were used to determine the effects of acid loading (by adding NH4Cl, 7.2 mmol/220 g body wt/day to food slurry for 7 days) on renal expression of claudins and then to evaluate whether the results were reversed by antagonizing calcium-sensing receptor (using NPS-2143). At the end of each animal experiment, the kidneys were harvested for immunoblotting, immunofluorescence microscopy, and quantitative PCR (qPCR) analysis of claudins and the calcium-sensing receptor. As expected, NH4Cl loading lowered urinary pH and increased excretion of urinary calcium and magnesium. In NH4Cl-loaded rats, renal protein and mRNA expression of claudin-16, and claudin-19, were decreased compared with controls. However, claudin-14 protein and mRNA increased in NH4Cl-loaded rats. Consistently, the calcium-sensing receptor protein and mRNA were up-regulated in NH4Cl-loaded rats. All these changes were reversed by NPS-2143 coadministration and were confirmed using immunofluorescence microscopy. Hypercalciuria and hypermagnesiuria in NH4Cl-loaded rats were significantly ameliorated by NPS-2143 coadministration as well. We conclude that in metabolic acidosis, claudin-16 and claudin-19 in the thick ascending limb are down-regulated to produce hypercalciuria and hypermagnesiuria via the calcium-sensing receptor.NEW & NOTEWORTHY This study found that the thick ascending limb of Henle's loop is involved in the mechanisms of hypercalciuria and hypermagnesiuria in metabolic acidosis. Specifically, expression of claudin-16/19 and claudin-14 was altered via up-regulation of calcium-sensing receptor in NH4Cl-induced metabolic acidosis. Our novel findings contribute to understanding the regulatory role of paracellular tight junction proteins in the thick ascending limb.

• Authors: Il Hwan Oh, Chor Ho Jo, Sua Kim, Sungsin Jo, Sungjin Chung, Gheun-Ho Kim
• Journal: American journal of physiology. Renal physiology (Am J Physiol Renal Physiol) Vol. 320 Issue 3 Pg. F418-F428 (03 01 2021) ISSN: 1522-1466 [Electronic] United States
• PMID: 33522409 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Calcium, Dietary
• Claudins
• Receptors, Calcium-Sensing
• Magnesium
• Calcium

Topics

• Acidosis (metabolism)
• Animals
• Calcium (metabolism)
• Calcium, Dietary (metabolism)
• Claudins (metabolism)
• Hypercalciuria (metabolism, pathology)
• Loop of Henle (metabolism, pathology)
• Magnesium (metabolism)
• Male
• Rats, Sprague-Dawley
• Receptors, Calcium-Sensing (metabolism)