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(Circulation Research. 2003;92:286.)
© 2003 American Heart Association, Inc.

Cellular Biology

Depletion of Intracellular Ca²⁺ Stores Sensitizes the Flow-Induced Ca²⁺ Influx in Rat Endothelial Cells

Hiu-Yee Kwan, Pan-Cheung Leung, Yu Huang, Xiaoqiang Yao

From the Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China.

Correspondence to Xiaoqiang Yao, PhD, Dept of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong. 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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