The immediate subendothelial connective tissue matrix consists of the basement membrane, a collagenous felt-like cell surface coat. The collagen from basement membranes has been isolated from human lung, skin, and kidney using a new fractionation method which separates native forms of collagen Types I, II, III, and IV. The Type IV collagens from the basement membranes have been characterized in respect to amino acid and carbohydrate composition, molecular size, charge and native structure. Antibodies prepared against the Type IV collagen reacted with both epithelial and vascular basement membranes as judged by immunofluorescence. Platelet-rich plasma (250,000/μl) from 5 normal subjects were tested for aggregation and 14C-serotonin release with human collagen Types I, II, III, and IV. Complete aggregation (100%) and 14C-serotonin release (80–100%) was obtained when Types I, II, and III were used. Human kidney, lung, and skin collagen Type IV (10–100μg/ml) did not aggregate platelets nor cause release of their contents. Pre-incubation of platelets and human collagen Type IV for periods of 30 minutes did not result in inhibition of platelet aggregation by Types I, II, or III.These data indicate that the collagenous component of the basement membrane, the first extra-vascular collagen to which a platelet is exposed, does not elicit aggregation as do the fibrillar collagens in the perivascular matrix.
Identification and characterization of a novel transcriptional silencer in the human collagen type IV gene COL4A2
