Name: aquaporins and membrane transport
Uploaded: 2023-04-30T10:10:47.000Z
Duration: 1 min 25 s
Channel: JoVE

Water molecules are polar in nature, hence, they cannot diffuse rapidly across the non-polar lipid bilayer.
Therefore, cell membranes have special channel proteins called aquaporins that selectively transport water molecules according to the osmotic gradient.
These proteins function as tetrameric clusters, with each monomer acting as an independent water channel.
A single aquaporin channel comprises six transmembrane alpha-helices connected by five loops, of which two hydrophobic loops contain a conserved amino acid motif &#8211; Asparagine-Proline-Alanine or NPA.
The NPA residues form a constricted site that confines the water molecules into a single file as they pass through the channel.
Additionally, repulsion from the hydrophobic walls of the channel accelerates the movement of the water molecules.
While passing through the constricted site, the oxygen atoms interact with the asparagine residues of the NPA motif, interrupting the hydrogen-bonded bridges between the water molecules that would have otherwise allowed protons to hop in and pass through the channel.
Disruption of the hydrogen-bonded network prevents proton movement, making the aquaporin selectively permeable to water.

aquaporins

Aquaporins

Aquaporins or AQPs are a family of integral membrane proteins whose primary function is to transport water, while some called aquaglyceroporins also transport glycerol. In addition, aquaporins have also been suspected to be involved in transporting volatile substances, such as carbon dioxide and ammonia, across membranes. Such AQPs that act as gas channels are often highly expressed in cells involved in the gaseous exchange, such as red blood cells, epithelial cells, and pulmonary capillaries.
In contrast, the water selective AQPs are widely expressed and are crucial in water-transporting organs and tissues such as the kidneys, the exocrine glands, and the central nervous system. Nonetheless, these channels are also found in the lungs, the skeletal muscles, and the gastrointestinal organs, although they may not be functionally significant. While the water-selective AQPs are essential for cell migration, neuroexcitation, and epithelial fluid transport, the aquaglyceroporins are involved in adipocyte metabolism, skin hydration, and cell proliferation.
Due to their involvement in physiological functions, overexpression or deficiency of AQPs have been associated with several human diseases, including renal dysfunction, epilepsy, skin disease, cancer, neurological disorder, and cardiac ailments. For example, mutations in human AQP1 or AQP2 can result in defective urine concentrating processes. In rare instances, loss of function mutation in AQP2 leads to non-X-linked nephrotic diabetes insipidus or NDI, a condition characterized by unusually high urine output. Similarly, mutations in the major intrinsic protein of AQP (AQP0) of the eye lens can lead to congenital cataracts. Due to their significance in various human illnesses, many scientists have shown active interest in targeting AQPs for therapy.
Although most aquaporins function as open channels, some of them, especially in plants, have evolved to have a gated mechanism. Such aquaporins close down in response to harsh conditions of the environment, such as drought, stress, or flooding, under which the exchange of water can be harmful to the organism.

Aquaporins or AQPs are a family of integral membrane proteins whose primary function is to transport water, while some called aquaglyceroporins also ...

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JoVE Core

Cell Biology

Unit 1

Channels and the Electrical Properties of Membranes

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KEY TERMS AND CONCEPTS

aquaporins and membrane transport

Aquaporins are membrane proteins that move water across cell membranes. Some aquaporins, called aquaglyceroporins, also transport glycerol. A few aquaporins may also help move volatile substances such as carbon dioxide and ammonia.

These channels are found in many different tissues. Water-selective aquaporins are important in the kidneys, exocrine glands, and central nervous system. Aquaporins that may act as gas channels are often highly expressed in red blood cells, epithelial cells, and pulmonary capillaries, where gas exchange occurs.

Aquaporins also support several cell functions. Water-selective aquaporins help with cell migration, neuroexcitation, and epithelial fluid transport. Aquaglyceroporins are involved in adipocyte metabolism, skin hydration, and cell proliferation.

Changes in aquaporin levels or function can be linked to disease. These proteins have been associated with renal dysfunction, epilepsy, skin disease, cancer, neurological disorder, and cardiac ailments. Mutations in AQP1 or AQP2 can disrupt urine concentration, and loss of AQP2 function can cause non-X-linked nephrotic diabetes insipidus, a condition with very high urine output. A mutation in AQP0, the major intrinsic protein of the eye lens, can lead to congenital cataracts.

Because of these connections, scientists are interested in aquaporins as possible therapy targets. Most aquaporins are open channels, but some plant aquaporins use a gated mechanism. These channels can close in response to drought, stress, or flooding, which helps prevent harmful water movement in harsh conditions.

Aquaporins and Membrane Transport

Aquaporins are membrane proteins that move water across cell membranes. Some aquaporins, called aquaglyceroporins, also transport glycerol. A few aquaporins may also help move volatile substances such as carbon dioxide and ammonia. These channels are found in many different tissues. Water-selective aquaporins are important in the kidneys, exocrine glands, and central nervous system. Aquaporins that may act as gas channels are often highly expressed in red blood cells, epithelial cells, and...

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the-role-of-ion-channels-in-neuronal-computation

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key terms and concepts

Explore how aquaporins move water and glycerol across membranes, affect cells and organs, and connect to disease in high school biology.

Aquaporins and Membrane Transport | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Aquaporins and Membrane Transport

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