Effect of thiazide on renal gene expression of apical calcium channels and calbindins.
Thiazide diuretics are specific inhibitors of the Na-Cl cotransporter in the distal convoluted tubule (DCT). In addition to producing diuresis and natriuresis, they have a hypocalciuric effect. Recently, two apical calcium channels have been identified, transient receptor potential vanilloid 5 (TRPV5) and TRPV6; both are expressed in the DCT. We studied the effects of thiazides on mouse renal calcium handling and renal gene expression of TRPV5 and TRPV6, as well as calbindin-D(28k) and calbindin-D(9k), both of which are calcium transport facilitators located in the DCT. Upregulation of renal TRPV5 was found 4 h after intraperitoneal injection of chlorothiazide (CTZ) at both 25 and 50 mg/kg, but not at 100 mg/kg. Chronic treatment with CTZ at 25 mg/kg twice daily for 3 days, with or without salt supplementation of 0.8% NaCl and 0.1% KCl in the drinking water, caused hypocalciuria, but the gene expression patterns were different. Without salt supplementation, mice developed volume contraction and there were no changes in gene expression. When volume contraction was prevented by salt supplementation, there was a significant increase in gene expression of TRPV5, calbindin-D(28k), and calbindin-D(9k). Salt supplementation alone also induced significant upregulation of TRPV5, TRPV6, and both calbindins. The upregulation of TRPV5 by CTZ and salt supplementation and salt alone was further confirmed with immunofluorescent staining studies. Our studies suggest that thiazides induce hypocalciuria through different mechanisms depending on volume status. With volume contraction, increased calcium reabsorption in the proximal tubule plays the major role. Without volume contraction, hypocalciuria is probably achieved through increased calcium reabsorption in the DCT by the activation of a transcellular calcium transport system and upregulation of apical calcium channel TRPV5, calbindin-D(28k), and calbindin-D(9k).
Lee
Chien-Te
CT
Division of Nephrology, Department of Medicine, Chang-Gung Memorial Hospital, Taiwan.
Shang
Shuhua
S
Lai
Li-Wen
LW
Yong
Kim-Chong
KC
Lien
Yeong-Hau H
YH
D000818:Animals; D064026:Calbindins; D002118:Calcium / Q000378:metabolism / Q000652:urine*; D015220:Calcium Channels / Q000235:genetics*; D002740:Chlorothiazide / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology; D004232:Diuretics; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation / Q000187:drug effects*; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D064030:S100 Calcium Binding Protein G / Q000235:genetics*; D049993:Sodium Chloride Symporter Inhibitors / Q000009:adverse effects / Q000494:pharmacology*; D050916:TRPV Cation Channels
D064026:Calbindins; D015220:Calcium Channels; D004232:Diuretics; D012333:RNA, Messenger; D064030:S100 Calcium Binding Protein G; D049993:Sodium Chloride Symporter Inhibitors; D050916:TRPV Cation Channels; C120776:TRPV6 channel; C492240:Trpv5 protein, mouse; D002740:Chlorothiazide; D002118:Calcium