Figure 12.

Tentative model of the pathways of water absorption across the intestinal epithelium in salmonids. An osmotic gradient is set up across the lateral membrane by means of the Na⁺, K⁺-ATPase. Water may be drawn osmotically through four pathways: (1) diffusion through the lipid bilayer of the enterocyte; (2) paracellular diffusion through the TJ; (3) symport with Na⁺ and glucose by the SGLT1; (4) diffusion through aquaporins apically as well as laterally. Aquaporins may be translocated between sub-apical vesicles and the cell membrane possibly regulated by phosphorylation events. The model is based on the elements investigated in the present paper. For simplicity apical ion-transporters are only shown in the upper enterocyte. LIS, lateral intercellular space; TJ, tight junction; Ves, intracellular vesicles.