examination of replicas of non-confluent monolayers of endothelial cells reveals the following intramembrane structures proposed as 'markers ' for the sequential events of synthesis and assembly of zonulae occludentes : development of surface contours consisting of elongate terraces and furrows ( valleys ) orientated parallel to the axis of cytoplasmic extensions of spreading endothelial cells , appearance of small circular pf face depressions ( or volcano-like protrusions on the ef face ) that represent cytoplasmic vesicle-plasma membrane fusion sites , which are positioned in linear arrays along the contour furrows , appearance of 13-15 nm intramembrane particles at the perimeter of the vesicle fusion sites , and alignment of these intramembrane particles into the long , parallel , anastomosed strands characteristic of mature tight junctions .
C0014257
endothelial
C0225336
endothelial cells