Fine structure of “intimal cushions” at branching sites in coronary arteries of vertebrates

A scanning and transmission electron microscopic study
  • T. Yohro
  • G. Burnstock


The branching sites of perfusion-fixed coronary arteries of Sprague-Dawley rat, zebra finch (Taeniopygia guttata) and lizard (Tiliza rugosa) were studied by scanning and transmission electron microscopy. The scanning microscopic appearance of intimal cushions is described for the first time in the present study.

With scanning microscopy, ridges were shown to project into the lumen at the branching sites. They were usually “O” or “U”-shaped and surrounded the orifice of the branch. Some of the ridges were arranged spirally around the orifice. These ridges appear to represent the “intimal cushions” described in previous studies of mammalian arteries with the light or transmission electron microscope. At lower magnification the cell borders of endothelial cells were observed as continuous, low ridges all around the cells but appeared as discontinuous ridges at higher magnification. Most endothelial cells of coronary arteries were flat and squamous with a slightly elevated nuclear region. However, those in the region of ridges or cushions were spindle-shaped and bulged more prominently into the lumen. Transmission microscopy showed that the cushions consisted of two different layers of smooth muscles. In arteries and larger arterioles the inner layer was characterized by the presence of irregular shaped smooth muscle cells with wide intercellular spaces between. In the adventitia of the branching sites a layer of longitudinally oriented smooth muscles was observed. The presence of this layer was a constant feature of the adventitia of the trunk near the branching sites in the three vertebrate species examined.

With transmission microscopy, a peculiar type of cushion was also observed in smaller arterioles. These cushions formed ridges projecting into the lumen and consisted of thickened endothelial cells and processes of smooth muscles. The main bodies of these smooth muscle cells were located within the media of the trunk, where their long axes were oriented in a different direction from that of the usual cells in the trunk. Frequent contact between the processes of endothelial cells and smooth muscle was noticed in this cushion, and many nerve profiles were observed nearby, especially around the trunk. These observations suggest that this type of cushion is closely associated with the precapillary sphincters.

Key words

Intima Coronary arteries Fine structure Vertebrates 


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Copyright information

© Springer-Verlag 1973

Authors and Affiliations

  • T. Yohro
    • 1
  • G. Burnstock
    • 1
  1. 1.Department of Anatomy, Faculty of MedicineUniversity of TokyoTokyoJapan

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