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Related Concept Videos

Transcellular Transport of Solutes01:23

Transcellular Transport of Solutes

Transcellular transport of solutes is the movement of substances like monosaccharides and amino acids through polarized cells. This transport mechanism is primarily seen in epithelial and endothelial cells aided by membrane transport proteins such as channels and transporters. The tight junctions between these cells confine the membrane proteins to the two sides of the cell. The epithelial cells have distinct apical and basolateral domains. In contrast, the endothelial cells show the luminal...
Membrane Proteins01:30

Membrane Proteins

Plasma membranes have integral transmembrane proteins involved in facilitated transport. These proteins are collectively referred to as transport proteins, and they function as either channels for the material or as carriers themselves. Channel proteins have hydrophilic domains exposed to the intracellular and extracellular fluids and a hydrophilic channel through their core that provides a hydrated opening for solutes to pass through the membrane layers. Passage through the channel allows...
Aquaporins01:25

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.
The Significance of Membrane Transport01:44

The Significance of Membrane Transport

The transport of solutes across the cell membrane is essential for metabolic processes, like maintaining cell size and volume, generating the action potential, exchanging nutrients and gases, etc. Membrane transport can be either passive or active. It can be simple diffusion, facilitated, or mediated transport aided by transport proteins such as transporters and channels.
Transporters facilitate either an active or passive movement of solutes. They can allow a single-molecule transport down its...
The Significance of Membrane Transport01:44

The Significance of Membrane Transport

The transport of solutes across the cell membrane is essential for metabolic processes, like maintaining cell size and volume, generating the action potential, exchanging nutrients and gases, etc. Membrane transport can be either passive or active. It can be simple diffusion, facilitated, or mediated transport aided by transport proteins such as transporters and channels.
Transporters facilitate either an active or passive movement of solutes. They can allow a single-molecule transport down its...
Fluid Movement Between Compartments01:18

Fluid Movement Between Compartments

The force applied by fluids against a surface, known as hydrostatic pressure, initiates the transfer of fluid among different compartments. Within our blood vessels, the blood's hydrostatic pressure is a result of the heart's pumping action. At the arteriolar end of capillaries, hydrostatic pressure (capillary blood pressure) exceeds the opposing colloid osmotic pressure created primarily by plasma proteins like albumin. This discrepancy in pressure propels plasma and nutrients from the...

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Related Experiment Video

Updated: Jun 16, 2026

Measuring the Osmotic Water Permeability Coefficient (Pf) of Spherical Cells: Isolated Plant Protoplasts as an Example
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Measuring the Osmotic Water Permeability Coefficient (Pf) of Spherical Cells: Isolated Plant Protoplasts as an Example

Published on: October 8, 2014

Water-transporting proteins.

Thomas Zeuthen1

  • 1Nordic Center for Water Imbalance Related Disorders, Institute of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, Blegdamsvej 3C, 2200N, Copenhagen, Denmark. tzeuthen@sund.ku.dk

The Journal of Membrane Biology
|January 22, 2010
PubMed
Summary

Water transport occurs via osmosis or cotransport with solutes. Cotransport, especially in epithelial cells, explains uphill water movement and ion-water coupling, challenging osmosis as the sole mechanism.

Area of Science:

  • Cellular Biology
  • Physiology
  • Membrane Transport

Background:

  • Water transport across cell membranes is crucial for physiological processes.
  • Osmosis, driven by osmotic pressure, is a primary model for water movement.
  • The role of cotransport in water transport remains incompletely understood.

Purpose of the Study:

  • To elucidate the mechanisms of water transport beyond simple osmosis.
  • To investigate the role of cotransport in epithelial water and ion transport.
  • To reconcile observed water transport phenomena with existing models.

Main Methods:

  • Review of existing literature on water transport mechanisms.
  • Analysis of water transport in various transporter types (cotransporters, uniporters).

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Expression, Solubilization, and Purification of Eukaryotic Borate Transporters
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Expression, Solubilization, and Purification of Eukaryotic Borate Transporters

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Last Updated: Jun 16, 2026

Measuring the Osmotic Water Permeability Coefficient (Pf) of Spherical Cells: Isolated Plant Protoplasts as an Example
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  • Consideration of experimental evidence, including aquaporin knockout studies.

    • Main Results:

    • Water transport occurs via osmosis, cotransport, or a combination of both.
    • Cotransport of water is coupled to substrate flux within protein pathways.
    • Specific transporters like K(+)/Cl(-) and Na(+)/K(+)/2Cl(-) cotransporters exhibit entirely cotransported water.
    • Glucose uniporters and Na(+)-coupled transporters utilize both osmosis and cotransport.
    • Water cotransport provides a mechanism for uphill water transport and ion-water coupling in epithelia.
    • Aquaporins enhance osmotic water transport, approaching isotonicity.

    Conclusions:

    • Water cotransport is a significant mechanism, particularly in epithelial transport, explaining uphill movement and ion-water coupling.
    • Osmosis alone cannot fully account for all observed water transport phenomena.
    • Understanding water cotransport is essential for comprehending epithelial physiology.