Heterogeneity in the distribution of actin filaments in the endothelial cells of arteries and arterioles in the rat kidney.

The distribution of actin filaments (AFs) in arterial and arteriolar endothelial cells (ECs) was examined in situ by staining with rhodamine-phalloidin in the rat kidney after perfusion-fixation under physiological pressure. ECs possessed two populations of AF bundles, namely, peripheral bands (PBs) at the cell border and stress fibers (SFs) in the cytoplasm. The distribution of AFs was heterogeneous and exhibited three patterns in the arterial tree. In large arteries (> 120 microns in luminal diameter) ECs contained predominantly PBs in addition to occasional SFs mainly in the upstream side of cells (PB-pattern). In arteries with intermediate diameters (30-120 microns), both PBs and SFs were conspicuous (PB-SF-pattern). In small arteries and arterioles (< 45 microns), SFs were prominent and PBs were rare (SF-pattern). In electron micrographs, we found that PBs were attached not to the lateral but to the basal plasma membrane via electron-dense materials and that SFs included two subpopulations, namely, thick basal and thin apical SFs. Morphometric analysis revealed that the length density of PBs was higher in segments with the PB-pattern than in those with the PB-SF-pattern. The length density of SFs was significantly higher in the SF-pattern than in the PB-SF-pattern, whereas there was little difference in this parameter among vessel segments with the SF-pattern. We suggest that PBs and SFs are fundamentally structures that anchor ECs on the substratum, and are differentiated according to their different mechanical burdens.