Figure 1.

A. Light micrograph of an untreated retinal arteriole stained with toluidine blue (converted to greyscale). The endothelial cells and smooth muscle cells are in tight apposition throughout the cross-section. Scale bar = 5 μm B. Electron micrograph at ×40,000 magnification of an untreated retinal arteriole. The basal lamina (BL) can be clearly seen between the endothelial cells (E) and the smooth muscle (SM). C. Light micrograph of a retinal arteriole treated with collagenase and protease for 20 min. The endothelial cells have completely pulled away from the overlying smooth muscle layer creating a 1-5 μm separation cleft. Scale bar = 5 μm D. Electron micrograph at ×28,000 magnification of a retinal arteriole treated with enzyme for 20 min. Remnants of digested basal lamina can be seen in the separation cleft (SC). Projections (P) normally connecting the endothelial cells to the smooth muscle layer have broken away. AJ, adheren junction. E. Photomicrograph of an untreated retinal arteriole anchored down in the physiological recording bath. Scale bar = 5 μm. F. The same vessel following 20 min digestion with collagenase and protease. The separation of the endothelial cells from the smooth muscle layer can be clearly visualised. Scale bar = 5 μm.