Vascular Endothelium - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 482

Tabl e 9. 8. Role of endothelial ion channels. Ion channel expression depends on cell culture
features and growth conditions, as well as endothelial cell type. Endothelial cells express numerous
ion channels that intervene in many processes between endothelial cells and between endothelial
cells and smooth myocytes. Two major functions of ion channels are the control of calcium influx
and the modulation of membrane potential. The membrane potential provides the electrochemical
driving force for Ca 2 + influx. In endothelial cells, Ca 2 + -dependent K + currents are modulated by
α 3 -integrin attachment to fibronectin. Potassium outflux through K IR channels enhances cell

migration.

β

V

Function Examples of produced mediators

Synthesis of vasoactive substances NO, ET, PGi2, TxA2

Production of hemostatic factors vWF, PAF, TPFI

Secretion of fibrinolytic factors tPA

Generation of growth factors EGF, FGF2/4, HGF, IGF1/2, PDGF, VEGF

Molecular transport Molecular machinery

Mechanotransduction NOS activation

Cell proliferation NO

Cell extravasation Cell adhesion molecules

Endothelial cell-matrix adhesion Cell adhesion molecules

Endothelial cell migration Chemokines

Angiogenesis Angiomotin, angiopoietin, angiokines,

growth factors, Notch, DCC, ephrin, EPH,
semaphorins, Slit-2/3, SlitR, VEGFR

9.5.4 Ion Carriers of Endothelial Cell

Ion channels abound in the plasma membrane of non-excitable endothelial cells
[ 895 ]. They control ion influx necessary to produce vasoactive molecules, pro- and
anticoagulants, growth factors, etc., that are released for storage or immediate action
(Table 9.8 ). They are involved in the regulation of cell transport. Angiogenesis
entails mediation of ion channels.
Endothelial cells undergo slow and more or less small changes in membrane
potential associated with the activity of plasmalemmal ion channnels and pumps.
The membrane potential of vascular endothelial cells is negative compared with
the blood and tissue. The membrane potential is in general more negative in
macrovascular than microvascular endothelial cells [ 895 ]. 37
Ion fluxes between endothelial cells, between endothelial and smooth muscle
cells across the basement membrane and myoendothelial junctions, and between
endothelial cell and migrating lymphocyte or monocyte, also occur through gap
junctions. The large variability in gap junctions depends on the connexin isoforms

37 The resting potential is mainly determined by K + channels, the expression of which varies
greatly among endothelial cell types. Vasoactive stimuli, such as acetylcholine, bradykinin, and
histamine, can cause membrane hyperpolarization.