Increased endothelin-1 expression in the kidney in hypercalcemic rats.
BACKGROUND
Although hypercalcemia causes diuresis and natriuresis, the molecular mechanisms of these effects are not well established. Recently, the important role of the calcium-sensing receptor (CaR) in hypercalcemia-induced polyuria was reported. Endothelin-1 (ET-1) that is locally produced in the nephron has been suggested to have the natriuretic and/or diuretic effects in the kidney. Therefore, we hypothesized that ET-1 expression could be increased through the activation of CaR in the kidney in hypercalcemia.


METHODS
Rats were made hypercalcemic by dihydrotachysterol (DHT) treatment. The urinary concentration of ET-1 and the mRNA expression of ET-1 in the kidney were determined. Immunohistochemistry was performed to determine types of the cells that produce ET-1. CaR and ET-1 promoter luciferase constructs were co-expressed in COS-7 cells and the ET-1 promoter activity following the addition of extracellular calcium was measured by the luciferase assay.


RESULTS
In hypercalcemic rat, urinary ET-1 excretion was increased by twofold, and ET-1 mRNA expression was increased in the kidney cortex by threefold. In cortical collecting duct (CCD), both principal cells and intercalated cells synthesized ET-1. In cells that express CaR, ET-1 promoter was activated in a dose-dependent manner by extracellular calcium over the range of 0.5 to 3.0 mmol/L.


CONCLUSIONS
First, activation of CaR increases ET-1 transcription in a dose-dependent manner. Second, hypercalcemia increases ET-1 production in the kidney cortex. These data suggest the possibility that CaR might play an important role in hypercalcemia-induced increase in ET-1 production.
Shiraishi
Naoki
N
Third Department of Internal Medicine, Kumamoto University School of Medicine, Kumamoto, Kumamoto, Japan.
Kitamura
Kenichiro
K
Kohda
Yukimasa
Y
Narikiyo
Takefumi
T
Adachi
Masataka
M
Miyoshi
Taku
T
Iwashita
Kozo
K
Nonoguchi
Hiroshi
H
Miller
R Tyler
RT
Tomita
Kimio
K
D000818:Animals; D019556:COS Cells; D004195:Disease Models, Animal; D004231:Diuresis / Q000502:physiology; D019332:Endothelin-1 / Q000097:blood / Q000235:genetics* / Q000652:urine; D005786:Gene Expression Regulation; D006934:Hypercalcemia / Q000097:blood / Q000503:physiopathology* / Q000652:urine; D007150:Immunohistochemistry; D007672:Kidney Cortex / Q000502:physiology*; D008297:Male; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D044169:Receptors, Calcium-Sensing / Q000378:metabolism
D019332:Endothelin-1; D012333:RNA, Messenger; D044169:Receptors, Calcium-Sensing