Water channel (PubMed:23893133). Channel activity is down-regulated by CALM when cytoplasmic Ca(2+) levels are increased. May be responsible for regulating the osmolarity of the lens. Interactions between homotetramers from adjoining membranes may stabilize cell junctions in the eye lens core (By similarity). Plays a role in cell-to-cell adhesion and facilitates gap junction coupling. Homotetramer (PubMed:15377788, PubMed:16309700). Homooctamer formed by head-to-head interaction between homotetramers from adjoining membranes (PubMed:15377788, PubMed:16309700). Interacts with CALM; one CALM molecule interacts with the cytoplasmic domains of two aquaporins, leading to channel closure (PubMed:23893133). Interacts (via C-terminus) with BFSP1 (via C-terminus) in aged lens fiber cells (PubMed:28259670). Major component of lens fiber gap junctions. Higher expression in pre-natal (1-5 months gestation) than in postnatal (4-6 months) calf lens. Aquaporins contain two tandem repeats each containing two membrane-spanning helices and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Each tandem repeat contains a loop and a short helix that enter and leave the lipid bilayer on the same side. Subject to partial proteolytic cleavage in the eye lens core. Partial proteolysis promotes interactions between tetramers from adjoining membranes (By similarity). Fatty acylated at Met-1 and Lys-238. The acyl modifications, in decreasing order of ion abundance, are: oleoyl (C18:1) > palmitoyl (C16:0) > stearoyl (C18:0) > eicosenoyl (C20:1) > dihomo-gamma-linolenoyl (C20:3) > palmitoleoyl (C16:1) > eicosadienoyl (C20:2). Belongs to the MIP/aquaporin (TC 1.A.8) family.