Knowledge Bank

Calcium (Ca2+) is a ubiquitous 2nd messenger, known to regulate many cellular pathways including muscle contraction, cell proliferation, and apoptosis. Deregulation of Ca2+ homeostasis is thought to play a role in vascular endothelial cell (EC) dysfunction, which shifts the endothelium to a pro-inflammatory state and initiates atherosclerosis. Since these cells are constantly exposed to fluid mechanical shear stress by blood flow, it is of particular interest to study the effect that shear stress has on the intracellular Ca2+ levels. It has been shown that when ECS are exposed to fluid shear stress, there is an increase in cytosolic Ca2+ levels. The three main sources of Ca2+, the endoplasmic reticulum (ER), the mitochondria, and the extracellular media, are all thought to play a role in this response. However, it is not known to what magnitude each source is responsible, nor by which pathway this response is initiated. The goal of the present study was to determine the influence each source possesses in regulating the Ca2+ response to shear stress, and how this occurs. To monitor the Ca2+ response to flow, ECs were incubated with the Ca2+-sensitive probe Fluo-4 and then subjected to shear stress in the presence or absence of specific chemicals to determine the source of the Ca2+ response. Specifically, when mitochondrial Ca2+ buffering was inhibited, the oscillatory Ca2+ response was effectively abolished. When the extracellular Ca2+ was eliminated, it had very little effect on the response. It was further determined that the phospholipase C (PLC)/G-protein /inositol triphosphate receptor (IP3R) pathway is directly involved in the response, whereas the mitochondrial Na+/Ca2+ exchanger (mNCX) plays a role in maintaining oscillations. A greater understanding of these phenomena could lead to better drug development to prevent and/or treat endothelial dysfunction, and ultimately combat cardiovascular disease.