when periodontal capillaries of rat incisor tooth were immunostained for four basement membrane components ( laminin , collagen iv , fibronectin , heparan sulfate proteoglycan ) , all four were detected in the secretory organelles of endothelial cells located within 3 mm of the tooth 's proximal end , but only the proteoglycan was observed in cells located 4 mm away and beyond ( experiment i ) .
C1327616
secretory
C0007634
cells