Intracellular Calcium Changes in Rat Aortic Smooth Muscle Cells in Response to Fluid Flow

Abstract

Vascular smooth muscle cells (VSM) are normally exposed to transmural fluid flow shear stresses, and after vascular injury, blood flow shear stresses are imposed upon them. Since Ca2+ is a ubiquitous intracellular signaling molecule, we examined the effects of fluid flow on intracellular Ca2+ concentration in rat aortic smooth muscle cells to assess VSM responsiveness to shear stress. Cells loaded with fura 2 were exposed to steady flow shear stress levels of 0.5-10.0 dyn/cm2 in a parallel-plate flow chamber. The percentage of cells displaying a rise in cytosolic Ca2+ ion concentration ([Ca2+]i) increased in response to increasing flow, but there was no effect of flow on the ([Ca2+]i) amplitude of responding cells. Addition of Gd3+ (10 microM) or thapsigargin (50 nM) significantly reduced the percentage of cells responding and the response amplitude, suggesting that influx of Ca2+ through ion channels and release from intracellular stores contribute to the rise in ([Ca2+]i) in response to flow. The addition of nifedipine (1 or 10 microM) or ryanodine (10 microM) also significantly reduced the response amplitude, further defining the role of ion channels and intracellular stores in the Ca2+ response.

Altered hemodynamics, endothelial function, and protein expression occur with aortic coarctation and persist after repair

“…Observed differences in active force across experimental groups are thought to be a result of changes in resting and active components of SM contraction, independent of intracellular Ca 2ϩ regulation. However, it is conceivable that observations may be a result of Ca 2ϩ -dependent pathways, including cGMP kinase and L-type channels, or Ca 2ϩ -independent G protein coupling, all of which serve to alter contractility in response to sustained hemodynamic stimuli (1,2,14,56). Future studies using inhibitors for Ca 2ϩ channels (verapamil) and agonist activation (phentolamine) are feasible using the current methods and will allow the determination of Ca 2ϩ -dependent regulation in contractile force response in untreated and corrected CoA.…”

Complex Hemodynamic Insult in Combination with Wall Degeneration at the Apex of an Arterial Bifurcation Contributes to Generation of Nascent Aneurysms in a Canine Model

“…Elevated WSS or WSSG levels disrupt the normal function of endothelial cells, stimulate gene transcription, and activate ion channels and the consequent reorganization of the cellular cytoskeleton. 5,21 The more substantial structural changes, which occur after 6 months, appear to involve the upregulation of MMP-2 and -9, both of which are implicated in aneurysmal disease.…”

“…20 Blood flow is generally considered an important modulator of normal artery enlargement in response to increased flow to maintain normal shear stress. 21 In this study, despite all models having simulated elastic fiber insults (arterial wall deterioration), nascent aneurysms were generated in only 5 of 9 models. We hypothesize that the bifurcation angle is an important factor because T-shaped bifurcations (146.8 Ϯ 40.84°) were more likely to induce the generation of aneurysms than Y-shaped bifurcations (87.25 Ϯ 18.87°).…”

Going With the Flow

“…For example, physiological levels of flow-induced shear stress (Ͻ10 dyn/cm 2 ) elevates the cytosolic Ca 2ϩ concentration in rat aorta smooth muscle cells through a mechanism that appears to involve, at least in part, Ca 2ϩ entry through a gadolinium-sensitive pathway. 8 This direct effect on vascular myocytes could underlie the vasoconstrictor response to flow that has been observed in a number of resistance arteries and small veins in vitro, as these responses were retained after removal of the endothelium, required Ca 2ϩ influx, and were inhibited by agents that block Ca 2ϩ entry into smooth muscle cells. 9 Indeed, flow has been shown to contract cultured aortic smooth muscle cells, although higher levels of shear stress (Ն11 dyn/cm 2 ) were required to produce this effect and it appeared to involve a Ca 2ϩ -independent signaling mechanism.…”