The interendothelial junction in myocardial capillaries: evidence for the existence of regularly spaced, cleft-spanning structures.
Water and hydrophilic solutes cross the endothelium of continuous capillaries via the paracellular cleft and possibly other routes. This pathway shows a selectivity to molecule size and charge. However, it is not yet known which systems confer this selectivity. Isolated rat hearts were perfusion-fixed through the coronary circulation, stained with lanthanum or tannic acid, and further processed for transmission electron microscopy. Thin sections viewed at x 160,000 magnification revealed regularly spaced, cleft-spanning structures in the wider zone of a small percentage of clefts in addition to at least one zonula occludens. Goniometric tilting of the specimen in steps of 5 degrees perpendicular to the plane of the wide zone showed that such "linkers" can be revealed in at least 40% of all clefts. They become visible at some tilt angles, although the same area of the cleft is featureless at other angles. Single linker spacing measurements were obtained using a computerized image analysis system, and compiled in a frequency distribution chart. On the basis of these data, two models of a regular linker distribution within the cleft are illustrated. Our results provide evidence for the presence of regularly spaced, cleft-spanning structures within the interendothelial cleft which may have implications for endothelial cell-cell adhesion and permeability.
Schulze
C
C
Department of Anatomy and Cell Biology, St Mary's Hospital Medical School, London, UK.
Firth
J A
JA
D000818:Animals; D002196:Capillaries / Q000648:ultrastructure; D003331:Coronary Vessels / Q000378:metabolism / Q000648:ultrastructure*; D004730:Endothelium, Vascular / Q000378:metabolism / Q000648:ultrastructure*; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D008854:Microscopy, Electron; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains