Cytoplasmic microfilaments in endothelial cells of flow loaded canine carotid arteries

Abstract

To observe cytoplasmic microfilaments in the endothelial cells of flow-loaded arteries, an arteriovenous shunt was constructed between the common carotid artery and the external jugular vein in 26 dogs. After measuring the flow rates of the arteries, the endothelial layer was examined ultrastructurally with a transmission electron microscope at three different times: 1 week (acute experiments), 2-4 weeks (subacute experiments), and 4-7 months (chronic experiments). Six-to seven-nanometer microfilaments were found forming bundles, which usually ran longitudinally along the long axis of the vessel. In the acute experiments, the bundles increased in the endothelial cells of the flow-loaded arteries. They showed incomplete striation and were mostly located close to the basal cell membrane. In the subacute experiments, they showed an increase with the development of cross-striation. The half-desmosomal structure of the basal cell membrane had developed a close connection to the bundles. In the chronic experiments, the bundles were especially conspicuous around the intercellular junction. Tennanometer microfilaments increased in the endothelial cells of the flow-loaded artery in the subacute and chronic experiments. We consider that the bundles of 6- to 7-nm microfilaments might be structures developed to combat wall shear stress corresponding to actin filament stress fibers.

Effects of Disturbed Flow on Endothelial Cells

“…35 An increase in shear stress in canine common carotid artery following the creation of an arteriovenous shunt with the external jugular vein causes an increase in EC stress fibers. 26 These results indicate that the in vitro finding of orientation of stress fibers parallel to directional shear stress also occurs in vivo.…”

“…It has been suggested that the prominent stress fibers with clear orientation at regions exposed to high levels of directional flows may help the ECs to withstand hemodynamic stress and maintain vascular integrity. 26,39 Partial obstruction of arteries causes ECs in regions immediately downstream of the narrowing, where shear stress is low and unsteady, to become polygonal in shape with a loss of stress fiber orientation, in contrast to the EC elongation and stress fiber alignment with flow in regions of normal or high shear stress. 35 An increase in shear stress in canine common carotid artery following the creation of an arteriovenous shunt with the external jugular vein causes an increase in EC stress fibers.…”

Vascular Mechanobiology Endothelial Cell Responses to Fluid Shear Stress

“…10 This morphological change is accompanied by cytoskeletal reorganization, with actin filaments becoming rearranged into bundles of stress fibers and aligned in the direction of the shear stress. [11][12][13] Vascular Tone When blood flow increases in vessels, they acutely dilate, and the dilation is mainly mediated by nitric oxide (NO) released by ECs. 14 A stimulatory effect of shear stress on NO production has been demonstrated in cultured ECs (Figure 1B), [15][16][17] and shear stress has been found to increase NO production via activation of endothelial NO synthase (eNOS) and upregulation of its gene expression.…”

Increase in endothelial cell density before artery enlargement in flow-loaded canine carotid artery.

“…In six of the shunted and in the two nonoperated animals, controlled pressure perfusion-fixatjon was carried out as described previously 20 by using 3% glutaraldehyde in phosphate buffer (pH 7.4). The height of an inflow reservoir and the outflow resistance were adjusted to maintain a constant perfusion pressure of 100 mm Hg.…”