Spectrum Library

Aquaporins at a glance

With a concentration of 55,000 mM, water is by far the most prevalent molecule in biological systems. For many years it was assumed that biological membranes are freely water permeable, so that the existence of a family of water channels would not have been predicted. However, biophysical studies in erythrocytes and kidney tubules in the 1960s through the 1980s revealed that some membranes are more water permeable than others and have certain biophysical properties, such as weakly temperature-dependent water transport and enhanced osmotic compared with diffusional water permeability, which suggested water movement through a pore-like pathway. The molecular identity of the first water channel, aquaporin 1 (AQP1), was reported in 1992 (Preston et al., 1992).

AQP1 had little similarity to other known proteins, except for the major integral protein (MIP) of lens fiber, which was subsequently renamed AQP0. Soon thereafter, additional AQP family members were identified from animal, yeast, bacterial and plant sources, with at least 13 AQPs in humans. This Cell Science at a Glance article aims to highlight the biological roles of mammalian AQPs. Although some roles of AQPs, such as their function in the concentration of urine and the secretion of gland fluid, were predictable, other roles, such as those in cell migration and neural signaling, were unexpected. Following a brief review of AQP structure, function and regulation, this article will focus on the physiological roles of AQPs, with an emphasis on current knowledge of the cellular mechanisms. In addition, aquaporinopathies – AQP-related human diseases – and possibilities for AQP-based therapeutics, will be discussed.

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