Zhang et al. 10.1073/pnas.0710986105. |
SI Experimental Methods
The micrographs of rat microvessels analyzed for pericyte coverage are taken from a previous study by our group (1). The details of animal preparation and tissue processing for electron microscopy are described in that publication. All animal protocols were approved by the Institutional Animal Care and Use Committee of the University of California, Davis. Briefly, venular microvessels from 25-45 mm in diameter were identified by blood flow pattern in the mesentery of anesthetized rats. Vessels were perfused with physiological saline (Ringer's solution) additionally containing BSA (10 mg/ml) and hydraulic conductivity (LP) was determined. At conclusion of LP measurement vessels were fixed in situ by flooding the tissue with ice-cold glutaraldehyde. The tissues were processed for standard transmission electron microscopy and embedded in eponate resin where the individual perfused vessels were identified and sectioned. Ten cross-sections taken from five vessels were examined for the present study (78 clefts). The vessel circumference was measured on the basement membrane of the endothelial cells. Pericyte coverage was also measured along the circumferential path between the endothelium and the overlying pericytes as the summed total length from edge to edge of each pericyte segment in a cross-section. Endothelial clefts were counted as covered by a pericyte if a segment of pericyte was overlying the abluminal cleft opening.