Renal Disease; Fluid and Electrolyte Disorders
John S. Axford, Chris A. O'Callaghan in Medicine for Finals and Beyond, 2023
Unlike many ions and molecules, water cannot be pumped directly in the body. Instead, water moves between sites by osmosis if there is an osmotic gradient and if the barrier separating the two sites contains pores or channels through which it can pass. Aquaporin molecules form water channels in most cell membranes. Intra- and extracellular fluid compartments are normally in approximate osmotic equilibrium. The Na+/K+ATPase pumps sodium out of cells and potassium into cells so: Intracellular fluid has high potassium and low sodium concentrations.Extracellular fluid has low potassium and high sodium concentrations.
Basics of CSF production
Jyotirmay S. Hegde, Hemanth Vamanshankar in CSF Rhinorrhea, 2020
Transport of water, solutes, and ions in a bi-directional manner, in response to both hydraulic pressure and passive osmotic gradients, is controlled by aquaporins. These are highly selective of the molecule being transported, and at the same time provide rapid transport.35 Of the many aquaporins found (about 14 are identified), six are reported to be present in the brain.36–38 Permeability is specific to each of them; AQP3 and 9- permeable to small solutes and water; AQP8 to ions; and AQP 1, 4, 5 are water permeable. Of these, AQP1 is important in CSF formation; AQP9 in energy metabolism; AQP4 in the clearance of K+ released in neuronal activity and formation/resolution of brain edema.36 AQP4 channels move water by simple diffusion and vesicular transport – this is currently the most accepted theory of the function of AQP4 (Figure 2.2 C).39 Further, AQP4-rich areas like BBB and glia limitans at the subpial zones may also act as water channels for ISF-CSF drainage in extreme conditions.40 The discovery of aquaporins by Peter Agre, which resulted in his receiving a Nobel Prize in Chemistry in 2003, has led us to a greater understanding of biological fluid homeostasis and turnover.41
History of Asphyxia-related Deaths
Burkhard Madea in Asphyxiation, Suffocation,and Neck Pressure Deaths, 2020
The working group of Kondo (see also Chapter 15) investigated the suitability of the expression of aquaporin-3 and aquaporin-1 as vitality markers of strangulation marks (Ishida et al. 2018). Aquaporins are membrane water channels that play critical roles in controlling the water contents of cells. They are expressed in many epithelia and endothelia that can regulate osmolality throughout the body. Aquaporin-1 is expressed in vascular endothelial cells throughout the body, including the skin. Epidermal aquaporin-3 is increased in a cutaneous burn wound. A total of 24 neck compression marks by ligatures were investigated. After immunostaining, a total of ten high power fields were selected randomly. Antemortem neck compression enhanced aquaporin-3 expression in the keratinocytes. These results have been confirmed by this author's own working group (Figure 1.40). Aquaporin-3 might be useful as a marker of all kinds of antemortem skin injuries.
Therapeutic effects of Bombax ceiba flower aqueous extracts against loperamide-induced constipation in mice
Published in Pharmaceutical Biology, 2023
Liuping Wang, Shiyuan Xie, Xuan Jiang, Caini Xu, Youqiong Wang, Jianfang Feng, Bin Yang
Aquaporins are mainly expressed in the intestinal canal (Sun et al. 2020), which mediate the passive transport of free water across biofilm, thereby maintaining the homeostasis of the intracellular and extracellular environment (Matsuzaki et al. 2004). Moreover, the abnormal expression of aquaporins in the gastrointestinal tract is related to the occurrence of some diseases, such as constipation, gastritis, diarrhoea and gastric cancer (Liu et al. 2020). AQP3 is an important aquaporin located in the colon and is permeable to water (Li and Wang 2017). Previously studies have revealed the relationship between AQP3 and constipation, particularly morphine-induced constipation (Kon et al. 2015), promotes AQP3 expression level in the colon and subsequently increases water absorption from the luminal side to vasculature, which dries and hardens stool (Ikarashi et al. 2016). In the present study, the expression level of AQP3 was detected and the results showed that phenolphthalein and BCE relieve the symptoms of loperamide-induced constipation by decreasing the level of AQP3 in the colon of mice. However, the precise mechanisms remain to be further elucidated.
The aquaporin-4 water channel and updates on its potential as a drug target for Alzheimer’s disease
Published in Expert Opinion on Therapeutic Targets, 2023
Bret Silverglate, Xiaoyi Gao, Hannah P. Lee, Peter Maliha, George T. Grossberg
Until the discovery of aquaporins in 1992, the general question of how water crossed biological membranes remained a mystery. While researching the Rhesus factor, Peter Agre’s team at Johns Hopkins made the serendipitous discovery of what is now known as aquaporin-1 [3]. Agre was later awarded the Nobel Prize in Chemistry in 2003 for this work. AQP4 was discovered nearly simultaneously by Agre’s group at Johns Hopkins University and Verkman’s group at UCSF and was so named because it was the fourth aquaporin discovered. Unlike the three previously discovered, it was localized primarily in the central nervous system (CNS) of rats, with only minute amounts found in the lungs and kidneys [4]. Thus, AQP4 was hypothesized to be a primary regulator of water balance in the CNS. Although there had been some previous descriptions of aquaporins in the CNS, Agre’s paper established the existence of a separate one located near-exclusively in the CNS [5,6].
Anti-cataract therapies: is there a need for a new approach based on targeting of aquaporins?
Published in Expert Opinion on Therapeutic Targets, 2021
Barbara K. Pierscionek
An important class of lens proteins, which are far lower in proportion that the crystallins, but which play a vital role in water transport, microcirculation and homeostasis in protein/water balance in the lens are the aquaporins [21]. Aquaporins are small membrane proteins found in a number of tissues in humans and animals. The three main aquaporins that are expressed in the human lens are aquaporin 0, 1, and 5 [21]. These aquaporins are water transporting proteins [22]. Aquaporin 0 (also known as Membrane Intrinsic Protein) is found in the fiber cells throughout the lens, constituting over half of the protein concentration of the cell membranes [22]. Aquaporin 1 is found in the epithelial cells [22] and aquaporin 5 has been detected in all parts of the lens [23] and is the second most prevalent of the aquaporins in mature lens fiber cells [23]. Aquaporin 7, an aquaglyceroporin which facilitates transport of small molecules as well as water and may be active in transport of nutrients, has also been detected in the eye lens epithelium [22]; it has a significantly lower water permeability than aquaporin 1 [24].
Related Knowledge Centers
- Alpha Helix
- Asparagine
- Bacteria
- Lipid Bilayer
- Proline
- Cell Membrane
- Ion Channel
- Protein Family
- Major Intrinsic Proteins
- Cell