[Current findings for the interpretation of "tight junctions" as lipid structures]

For the interpretation of tight junction strands to be formations of lipids and not of proteins hitherto no demonstration of such structures in lamellar systems of pure lipids was known. The demonstration of such fibrillar structures with the freeze-fracture technique in bilayers of a dipalmitoylphosphatidylcholine-cholesterol system with a low content of cholesterol is presented. The fibrils represent obviously cylindrical, inverted micelles (H11-orientation). The mechanism of their formation within one bilayer enables the explanation of the occurrence of two tight-connected fibrils in tight junction strands. The intramembranous inverted micelles are stable structures concerning a reintegration into the lamellar arrangement, but breaking in short pieces, also in spherical micelles (lipidic particles), can occur.