title: Tunnel capillaries of cardiac myocyte in pressure-overloaded rat heart-an ultrastructural three-dimensional study.
abstract: To characterize the configuration of "tunnel capillaries" in myocytes, an ultrastructural three-dimensional (3-D) study was performed on pressure-overloaded rat hearts induced by 16-week constriction of the ascending aorta. The hearts showed high incidence (6.1 +/- 3.6%) of tunnel capillary formation. Eighty-two myocytes (26.4%) had tunnel capillaries in a cubic block of 120 x 656 x 446 micron3, which provided 1000 ultrathin serial sections. The cross-sectional area (925 +/- 226 micron2) of myocytes with tunnel capillaries was significantly larger than that of myocytes without tunnel capillaries (702 +/- 196 micron2) (P < 0.0001). There were three types of tunnel capillaries. Type I (13%) started from one intercellular capillary, ran across the myocyte, and then merged with other intercellular capillaries. Type II tunnel capillaries (87%) entered the myocyte from one intercellular capillary and ended within the myocyte. Type III tunnel capillaries were characterized by various combination of types I and II, forming a tunnel capillary network. Tunnel capillaries usually entered a myocyte at the place where the myocyte split or indented. Although some tunnel capillaries might be newly formed by angiogenesis, our 3-D study suggests that some of them are a deformation consequence of the myocardium remodeling in response to pressure overloading.
mesh_terms: D000818:Animals; D001794:Blood Pressure; D002196:Capillaries / Q000503:physiopathology* / Q000648:ultrastructure*; D003331:Coronary Vessels / Q000503:physiopathology / Q000648:ultrastructure; D006321:Heart / Q000503:physiopathology*; D007091:Image Processing, Computer-Assisted; D008297:Male; D008833:Microcirculation; D008854:Microscopy, Electron; D009206:Myocardium / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley