title: Fluid shear attenuates endothelial pseudopodia formation into the capillary lumen.
abstract: OBJECTIVE
  Endothelial cells have the ability to undergo morphological shape changes, including projection of cytoplasmic pseudopodia into the capillary lumen. These cytoplasmic projections significantly influence the hemodynamic resistance to blood flow. To examine mechanotransduction mechanisms, we investigated in vivo the hemodynamic conditions in capillaries that control endothelial pseudopod formation.
  
  
  METHODS
  Capillaries in rat skeletal muscle were fixed under carefully controlled perfusion conditions. The formation of endothelial pseudopodia were observed in cross-sections with electron microscopy and quantified with differential interference contrast microscopy under physiological, stasis, and reperfusion flow conditions.
  
  
  RESULTS
  Application of physiological levels of fluid flow prevents capillary endothelium to project pseudopodia into the capillary lumen. Reduction of fluid flow to near zero promotes the incidence of pseudopod projection from 5% to 55% of capillaries. After capillary pseudopodia have formed under static conditions, about one-half retract upon restoration of fluid flow. The presence of red blood cells in the capillary lumen prevents pseudopod formation.
  
  
  CONCLUSIONS
  The results suggest that there is a mechanism that serves to control cytoplasmic projections in capillary endothelium that is under the control of hemodynamic fluid stress. Investigation of pseudopodia growth on endothelial cells may be significant in understanding capillary obstruction in cardiovascular diseases.
authors.affiliation: Department of Bioengineering, The Whitaker Institute for Biomedical Engineering, University of California-San Diego, La Jolla, California 92093-0412, USA. ihueck@ucsd.edu
authors.forename: Isgard S
authors.initials: IS
authors.lastname: Hueck
authors.forename: Katharine
authors.initials: K
authors.lastname: Rossiter
authors.forename: Gerhard M
authors.initials: GM
authors.lastname: Artmann
authors.forename: Geert W
authors.initials: GW
authors.lastname: Schmid-Schönbein
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology*; D002196:Capillaries / Q000502:physiology* / Q000648:ultrastructure; D042783:Endothelial Cells / Q000502:physiology* / Q000648:ultrastructure; D004912:Erythrocytes / Q000502:physiology / Q000648:ultrastructure; D008297:Male; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology / Q000648:ultrastructure; D011554:Pseudopodia / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D033081:Shear Strength / Q000502:physiology