Water transport across mammalian cell membranes

Abstract

This review summarizes recent progress in water-transporting mechanisms across cell membranes. Modern biophysical concepts of water transport and new measurement strategies are evaluated. A family of water-transporting proteins (water channels, aquaporins) has been identified, consisting of small hydrophobic proteins expressed widely in epithelial and nonepithelial tissues. The functional properties, genetics, and cellular distributions of these proteins are summarized. The majority of molecular-level information about water-transporting mechanisms comes from studies on CHIP28, a 28-kDa glycoprotein that forms tetramers in membranes; each monomer contains six putative helical domains surrounding a central aqueous pathway and functions independently as a water-selective channel. Only mutations in the vasopressin-sensitive water channel have been shown to cause human disease (non-X-linked congenital nephrogenic diabetes insipidus); the physiological significance of other water channels remains unproven. One mercurial-insensitive water channel has been identified, which has the unique feature of multiple overlapping transcriptional units. Systems for expression of water channel proteins are described, including Xenopus oocytes, mammalian and insect cells, and bacteria. Further work should be directed at elucidation of the role of water channels in normal physiology and disease, molecular analysis of regulatory mechanisms, and water channel structure determination at atomic resolution.

AQP2 in human urine is predominantly localized to exosomes with preserved water channel activities

“…This is also the first report on the measurement of the Pf in the EVs. The value obtained (4.75 × 10 −4 cm s −1 ) was much smaller than the values reported for kidney proximal tubule brush border membrane vesicles and erythrocytes (~ 100 × 10 −4 cm s −1 ) [17,21]. The reasons for this discrepancy can be multifold.…”

Overexpression of AQP5, a putative oncogene, promotes cell growth and transformation

“…Aquaporin 5 (AQP5) is a member of the aquaporin (AQP) family of transmembrane water channel proteins which are widely distributed in various tissues throughout the body and play a major role in transcellular and transepithelial water movement [1,2]. Similar to the other AQPs, AQP5 consists of six transmembrane domains separated by five connecting loops, A-E [3] (Fig.…”

Vitrification of human early cavitating and deflated expanded blastocysts: clinical outcome of 474 cycles

“…In the later stage embryos like morula and blastocysts the water/cryoprotectant permeability is by facilitated diffusion via channel process. This process enables rapid permeation resulting in less time for equilibration with the cryoprotectants [26]. As exposure time to the high concentration of cryoprotectant solution is a crucial factor for the success of a vitrification protocol any process which decreases the equilibration time results in better survival of embryos.…”