Published online before print January 2, 2003, doi: 10.1161/01.RES.0000054625.24468.08
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Submitted on January 30, 2002
Revised on June 11, 2002
Accepted on December 18, 2002
Depletion of Intracellular Ca2+ Stores Sensitizes the Flow-Induced Ca2+ Influx in Rat Endothelial Cells
Hiu-Yee Kwan ;
From the Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China.
* To whom correspondence should be addressed. E-mail: yao2068{at}cuhk.edu.hk.
Hemodynamic shear stress elicits a rise in endothelial [Ca2+]I, which may serve as a key second messenger to regulate many flow-associated physiological and biochemical processes. In the present study, we used Mn2+ quenching of fluorescent dye Fluo3 as an assay to investigate the Ca2+ influx of rat aortic endothelial cells in response to flow. We found that the Ca2+ signaling in response to flow could be greatly influenced by the status of intracellular Ca2+ stores. Depletion of intracellular Ca2+ stores by thapsigargin (4 µmol/L) or cyclopiazonic acid (10 µmol/L) drastically sensitized the Ca2+ influx in response to flow. Ca2+-mobilizing agonist bradykinin (100 nmol/L) or ATP (100 µmol/L) had similar sensitizing effect. The effect of bradykinin or ATP was blocked by Xestospongin C and U73122, suggesting that the sensitization was related to the IP3-mediated store depletion. On the other hand, the Mn2+ quenching in response to flow was greatly reduced by ochratoxin A (100 nmol/L), an agent that could increase the filling state of intracellular Ca2+ stores. In addition, we found that depletion-sensitized Ca2+ influx in response to flow was mediated by a PKG-inhibitable cation channel and that the influx was affected by membrane potential and K+ channel activity. In conclusion, the present study argues for a critical role of intracellular Ca2+ status in determining the Ca2+ signaling in response to flow and it provides a general mechanistic explanation for the stimulatory role of blood-borne agonists on flow-induced Ca2+ influx.
Key words: flow shear stress • mechanotransduction • calcium • store depletion • ion channel
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