Water channel that mediates water transport across cell membranes irrespective of the cytosolic pH (PubMed:12084581, PubMed:21733844, PubMed:23382902, PubMed:30420639). The channel is permeable to glycerol, especially when the cytosolic pH is acidified (PubMed:21733844, PubMed:30420639). Contributes to adipocyte water and glycerol permeability, and may thereby contribute to the utilization of glycerol derived from phospholipid degradation (PubMed:23382902). May contribute to water transport in the intestine (Probable). Water channel that mediates water transport across cell membranes, but that is not permeable to glycerol. Homotetramer. Detected around lipid droplets. Detected in epithelial cells on villi in the ileum, and also in stomach, jejunum, colon, rectum, white adipose tissue and placenta (at protein level) (PubMed:15221416, PubMed:23382902). Expressed in duodenum and jejunum. Highest expression in absorptive epithelial cells at the tips of villi in the jejunum (PubMed:11573934, PubMed:12084581). Detected in subcutaneous adipose tissue (PubMed:23382902). Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Belongs to the MIP/aquaporin (TC 1.A.8) family. Acidification of the cytosol strongly increases channel permeability to glycerol (PubMed:30420639). Initial experiments showed that isoform 2 is permeable to water, but not to glycerol, but these results were obtained without lowering the cytosolic pH (PubMed:11573934).