Heterogeneous responsiveness of the in situ rat vascular endothelial cells to mechanical stretching in vitro.

En face endothelial cell (EC) sheets from various vessels of the rat vascular tree were stained with rhodamine-phalloidin to examine the response of the ECs to mechanical stretching, especially from the viewpoint of actin stress fiber (SF) dynamics. Arterial ECs were classified into three types according to the distribution pattern of their SFs before and after stimulation. In both ECs with few SFs from arteries near the heart and those having many SFs from arteries distributed in the uterus, ovary or kidney, new SF formation was not induced by stretching. ECs with various amounts of SFs from the abdominal aorta to the femoral artery developed many SFs in response to stretching. On the other hand, the response of venous ECs with initially few SFs was generally low, although active SF formation was observed in ECs from the uterine vein, portal vein and anterior facial vein, which are normally subjected to higher levels of mechanical stress in situ. The amplitude of stretching necessary for SF formation in ECs was about 40% in both vascular systems, although the time necessary for SF expression was 10 min and 30 to 40 min in arterial and venous ECs, respectively. A rapid increase in the number of ECs with SFs for a given amplituding of stretching suggests the presence of a threshold-like value in this reaction system. It was clarified that notable heterogeneity of ECs in their response to mechanical stress exists among the arterial and venous trees.