Figure 10.

The hypothetical scheme of the lipid transcytosis in enterocyte of the newborn rats. (A) Micelles containing lipids and surrounded with bile acid molecules (black dots) passed through glycocalyx and contact with the apical plasma membrane of microvilli. Then FFAs and cholesterol are subjected to flip-flop. During apical endocytosis, the membrane remnants (grey lines inside endosomes) could be captured from gut. Next, FFAs and cholesterol diffuse along the cytosolic leaflet to the contact sites between membranes of endosome and the ER. (B) In endosomes, FFAs and cholesterol are captured by the yet-unknown lipid transfer protein(s) (oval dots with a line inside) and appear in the membrane of the ER. Green arrows show the ER-derived lipid droplets. Then, their pathway is identical to that in adult rats (see Figure 10). The chylomicrons are formed with the help of ApoB. Alternatively, triacylglycerols and cholesterol ethers are accumulated inside the membrane of the ER and the lipid droplets (black arrows) are formed. Chylomicrons in newborn rats are larger than those in adult rats when their enterocytes obtained normal amounts of lipid (see Figure 9). These chylomicrons passed across the Golgi complex and were secreted into interstitial space where they could fuse with each other. (C) Finally, large chylomicrons are captured by lymphatic capillaries and appear in their lumen (L). Red arrows indicate the anchor filaments. (D) Large chylomicron. (E) 3D model of lymphatic capillary.