Expression of a functional extracellular calcium-sensing receptor in human aortic endothelial cells.
Extracellular Ca(2+) concentration ([Ca(2+)](o)) regulates the functions of many cell types through a G protein-coupled [Ca(2+)](o)-sensing receptor (CaR). Whether the receptor is functionally expressed in vascular endothelial cells is largely unknown. In cultured human aortic endothelial cells (HAEC), RT-PCR yielded the expected 555-bp product corresponding to the CaR, and CaR protein was demonstrated by fluorescence immunostaining and Western blot. RT-PCR also demonstrated the expression in HAEC of alternatively spliced variants of the CaR lacking exon 5. Although stimulation of fura 2-loaded HAEC by several CaR agonists (high [Ca(2+)](o), neomycin, and gadolinium) failed to increase intracellular Ca(2+) concentration ([Ca(2+)](i)), the CaR agonist spermine stimulated an increase in [Ca(2+)](i) that was diminished in buffer without Ca(2+) and was abolished after depletion of an intracellular Ca(2+) pool with thapsigargin or after blocking IP(3)- and ryanodine receptor-mediated Ca(2+) release with xestospongin C and with high concentration ryanodine, respectively. Spermine stimulated an increase in DAF-FM fluorescence in HAEC, consistent with NO production. Both the increase in [Ca(2+)](i) and in NO production were reduced or absent in HAEC transfected with siRNA specifically targeted to the CaR. HAEC express a functional CaR that responds to the endogenous polyamine spermine with an increase in [Ca(2+)](i), primarily due to release of IP(3)- and ryanodine-sensitive intracellular Ca(2+) stores, leading to the production of NO. Expression of alternatively spliced variants of the CaR may result in the absence of a functional response to other known CaR agonists in HAEC.
Ziegelstein
Roy C
RC
Johns Hopkins University School of Medicine, Johns Hopkins Bayview Medical Center, Division of Cardiology, Baltimore, MD 21224-2780, USA.
Xiong
Yali
Y
He
Chaoxia
C
Hu
Qinghua
Q
D001011:Aorta / Q000166:cytology*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D009569:Nitric Oxide / Q000096:biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D044169:Receptors, Calcium-Sensing / Q000819:agonists / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; D034741:RNA, Small Interfering; D044169:Receptors, Calcium-Sensing; D009569:Nitric Oxide; D002118:Calcium