Abundant, uniquely oriented endoplasmic reticulum in capillaries of the CNS: demonstration using reduced-osmium and glucose-6-phosphatase cytochemistry.
In the endothelial cells of capillaries in the rat CNS, we have observed abundant, circumferentially oriented, smooth, membrane-bound profiles, found just beneath, and parallel to, the abluminal plasmalemma. These structures are seen particularly well in tissue exposed to potassium ferricyanide-reduced OsO4. We studied these structures cytochemically, using glucose-6-phosphatase as a marker for endoplasmic reticulum, and acid phosphatase as a marker for the Golgi-associated endoplasmic reticulum containing lysosomal enzymes (GERL). We found that they contained glucose-6-phosphate hydrolyzing activity but did not contain acid phosphatase activity. Comparable structures were not seen in the continuous capillaries of skeletal muscle. Based on their morphology and content of glucose-6-phosphate hydrolyzing activity, we conclude that these structures are uniquely oriented smooth endoplasmic reticulum, which is much more abundant in capillaries of the CNS than in other continuous capillaries. The function of this distinctive feature of the CNS capillary is not known.
D000818:Animals; D002196:Capillaries / Q000201:enzymology*; D002531:Cerebellum / Q000098:blood supply*; D002560:Cerebrovascular Circulation; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D005260:Female; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D006651:Histocytochemistry; D008297:Male; D009993:Osmium Tetroxide; D051381:Rats; D011919:Rats, Inbred Strains
D005952:Glucose-6-Phosphatase; D009993:Osmium Tetroxide