title: Up-regulation of endothelial stretch-activated cation channels by fluid shear stress.
abstract: OBJECTIVE
  Stretch-activated cation channels (SAC) have been suggested to act as endothelial mechanosensors for hemodynamic forces. Ca(2+) influx through SAC could induce an intracellular Ca(2+) signal stimulating Ca(2+)-dependent synthesis of vasodilators like NO, prostacyclin, or EDHF. In the present study we tested whether laminar shear stress (LSS) regulates SAC function.
  
  
  METHODS
  Electrophysiological properties of SAC were investigated in human umbilical vein endothelial cells (HUVEC) subjected to defined levels of LSS in a flow-cone apparatus.
  
  
  RESULTS
  In HUVEC, we identified a Ca(2+) permeable SAC that was activated by membrane stretch. Single-channel current densities of SAC in cell-attached patches were significantly increased in HUVEC exposed to an LSS of 5 dyn/cm(2) for 4 h (1.15+/-0.17 SAC/patch) compared to HUVEC kept in stationary culture (0.46+/-0.07 SAC/patch). Exposure of HUVEC to a higher LSS of 15 dyn/cm(2) for 4 h induced similar up-regulation of SAC (1.27+/-0.21 SAC/patch). After 24 h exposure to LSS of 15 dyn/cm(2), single-channel current densities of SAC remained up-regulated (1.07+/-0.18 SAC/patch) compared to controls. In addition, stretch-sensitivity of SAC (channel activity NP(o) at -30 mmHg) significantly increased after 2 h of exposure to LSS of 5 and 15 dyn/cm(2) and remained up-regulated after 24 h. Inhibition of protein kinases and tyrosine kinases by H7 and genistein, respectively, prevented LSS-induced alteration of SAC function.
  
  
  CONCLUSIONS
  Single-channel current density and mechanosensitivity of SAC in HUVEC is up-regulated by LSS. Up-regulation of SAC function leads to enhanced mechanosensitive Ca(2+) influx, and represents a novel adaptive mechanism of the endothelium in the presence of altered hemodynamic forces.
authors.affiliation: Department of Nephrology, Universitätsklinikum Benjamin Franklin, Hindenburgdamm 30, D-12200 Berlin, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Brakemeier
authors.forename: Ines
authors.initials: I
authors.lastname: Eichler
authors.forename: Hartmut
authors.initials: H
authors.lastname: Hopp
authors.forename: Ralf
authors.initials: R
authors.lastname: Köhler
authors.forename: Joachim
authors.initials: J
authors.lastname: Hoyer
mesh_terms: D015220:Calcium Channels / Q000378:metabolism*; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology; D006801:Humans; D009200:Myocardial Contraction / Q000502:physiology*; D018408:Patch-Clamp Techniques; D047428:Protein Kinase Inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D012039:Regional Blood Flow / Q000502:physiology; D013314:Stress, Mechanical
chemical_list: D015220:Calcium Channels; D004791:Enzyme Inhibitors; D047428:Protein Kinase Inhibitors; D019833:Genistein; D011505:Protein-Tyrosine Kinases