Flow-induced changes in Ca2+ signaling of vascular endothelial cells: effect of shear stress and ATP

Abstract

The effect of hemodynamic flow on apparent cytosolic free Ca2+ concentration ([Ca2+]i) of cultured bovine aortic endothelial cells was examined in the absence and presence of adenine nucleotides using microfluorimetric analysis of fura-2 fluorescence. In the absence of adenine nucleotides, flow-induced shear stress produced little change (less than 10 nM) in [Ca2+]i. Similar results were obtained using calf pulmonary artery and human umbilical vein endothelial cells. However, addition of the adenine nucleotides ATP, ADP, or AMP under flow conditions produced a transient peak increase in [Ca2+]i that was followed by a sustained elevation. The rank order of potency for the peak response was ADP greater than or equal to ATP much much greater than AMP. Adenosine was without effect on [Ca2+]i. Washout of ATP resulted in the immediate return of [Ca2+]i to basal values, indicating that the effect of ATP was rapidly reversible. Decreasing the flow rate to zero during the sustained phase also resulted in an immediate decrease of [Ca2+]i. Similar results were obtained with ADP and AMP but not with the nonhydrolyzable adenine nucleotide analogues alpha,beta-methyleneadenosine-5'-diphosphate, beta,gamma-imidoadenosine-5'-triphosphate, or beta,gamma-methyleneadenosine-5'-triphosphate. Furthermore, the rate of [Ca2+]i decrease upon cessation of flow during the sustained phase of the response to ATP was inversely proportional to the ATP concentration. These results suggest that hydrolysis of ATP to adenosine by the ectonucleotidase is responsible for the termination of the ATP response under zero-flow conditions. Evaluation of the dose- and flow-dependent response of the cells to ATP indicates that convective-diffusive transport of ATP may play an important role in regulation of endothelial cell [Ca2+]i in presence of ectonucleotidase activity and could have important consequences for the regulation of blood flow in the vasculature.

Activation of AT 2 Receptors by Endogenous Angiotensin II Is Involved in Flow-Induced Dilation in Rat Resistance Arteries

“…In support of the second possibility, it has been shown that flow increases the availability of agonists by influencing their mass transport. 32,33 Nevertheless, the precise mechanism of AT 2 -dependent flow dilation remains to be elucidated. In the present study, AT 2 -dependent vasorelaxation represented a 10-m increase in diameter.…”

MAPKs (ERK½, p38) and AKT Can Be Phosphorylated by Shear Stress Independently of Platelet Endothelial Cell Adhesion Molecule-1 (CD31) in Vascular Endothelial Cells

“…These mechanical forces induce morphological, physiological, and biochemical changes of ECs (1,2). Although mechanisms for mechanosensing and subsequent signaling events in ECs have not yet been well characterized, activation of trimeric G proteins (3)(4)(5)(6), Ca 2ϩ mobilization (7)(8)(9)(10), and increased K ϩ efflux (11,12) are known as early signaling events. Other investigators have recently demonstrated that a glycoprotein, platelet endothelial cell adhesion molecule-1 (PECAM-1) is rapidly tyrosine-phosphorylated in bovine ECs (BAEC) exposed to fluid flow; this is thought to play important roles in transducing chemical stimuli received on the cell surface to the cytoplasmic aspects of the cell (13,14).…”

Fluid Shear Stress Induces Heat Shock Protein 60 Expression in Endothelial Cells In Vitro and In Vivo

“…16 Although the effect of inflammatory mediators and cytokines on endothelial cells has been extensively studied, less is known about the effect of shear stress. Endothelial cells rapidly respond to a change of shear stress by signal transduction events, such as an increase of intracellular calcium, [17][18][19] decrease of intracellular pH, 20 or increase of inositol trisphosphate and diacylglycerol. 21,22 The expression of many genes is altered by shear stress.…”