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Renal Disease; Fluid and Electrolyte Disorders
Published in John S. Axford, Chris A. O'Callaghan, 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.
Altitude, temperature, circadian rhythms and exercise
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Henning Wackerhage, Kenneth A. Dyar, Martin Schönfelder
So how does the thermoregulatory centre regulate sweating? A key brain area for sweating seems to be the brainstem and here the rostral ventromedial medulla, which is activated when humans sweat (52). This then innervates sweat glands through neurons that use acetylcholine and noradrenaline as neurotransmitters. Acetylcholine is the key neurotransmitter for sweating in response to temperature, as especially the eccrine sweat glands express the acetylcholine-binding M3-muscarinic receptors and some noradrenaline-binding adrenoceptors (48). The M3-muscarinic receptors are coupled to G proteins which then via some intermediate steps triggers a Ca2+ release, which, in turn, induces a translocation of aquaporin 5 water channels to the membrane. More aquaporin 5 channels in the membrane allow more water to enter the sweat gland, resulting in sweat production and secretion (48). The Aquaporin 5 (gene symbol: Aqp5) water channel seems essential for sweating, because the number of active sweat glands is dramatically reduced in Aqp5 knockout mice (53).
Hyponatremia in pregnancy
Published in Nadia Barghouthi, Jessica Perini, Endocrine Diseases in Pregnancy and the Postpartum Period, 2021
Anthony Parravani, Bethany Pellegrino
Nonpregnant state, maintenance of serum osmolality and sodium:Under nonpregnant conditions, serum osmolality is maintained within a narrow range of 275–295 mOsm/L.Any changes in serum osmolality are sensed by osmoreceptors which respond to correct the change.An increase in serum osmolality by 1–2% results in the release of ADH from the posterior pituitary, which acts on the Arginine Vasopressin Receptor 2 (AVPR2) on the basolateral membrane of the collecting ducts in the kidneys. This leads to the upregulation of aquaporin 2 channels and increased water absorption by the kidneys.Any increase in serum osmolality also stimulates the thirst center in the hypothalamus, resulting in water intake to assist in correction of the hypertonic state.4
Anti-cataract therapies: is there a need for a new approach based on targeting of aquaporins?
Published in Expert Opinion on Therapeutic Targets, 2021
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].
Optimization of an oral mucosa in vitro model based on cell line TR146
Published in Tissue Barriers, 2020
Grace C. Lin, Tamara Leitgeb, Alexandra Vladetic, Heinz-Peter Friedl, Nadine Rhodes, Angela Rossi, Eva Roblegg, Winfried Neuhaus
Aquaporins (AQP), integral membrane proteins forming water channels for rapid fluid transport, are very strongly expressed by, e.g., the salivary glands. Therefore, characterization of aquaporins is mostly referred to mouse, rat, or human salivary glands, but a thorough characterization for the human oral mucosa is still missing.70 In our oral mucosa model, we demonstrated the expression of AQP1, AQP3, AQP6, AQP7, AQP9, AQP10, and AQP11. The biopsy samples of the human oral mucosa showed a similar expression pattern as our model. A consistent expression for AQP1, AQP3, AQP7, AQP9, AQP10, and AQP11, a weak expression for AQP4 and no expression for AQP6, AQP8 and AQP12A was obtained. This confirms the similarity of our cell line-based model to the human model. Even though the expression of aquaporins was mostly described in the salivary glands, AQP3 and AQP9 were also found in rat buccal mucosa epithelium at the mRNA and protein level. Moreover, a correlation was suggested between AQP3 localization and the differentiation of keratinocytes.71 To understand the expression of aquaporins in our human buccal mucosa model, further investigations on their functionality in the oral mucosa are necessary.
A New Rabbit Model of Chronic Dry Eye Disease Induced by Complete Surgical Dacryoadenectomy
Published in Current Eye Research, 2019
Robert Honkanen, Wei Huang, Liqun Huang, Kevin Kaplowitz, Sarah Weissbart, Basil Rigas
Complete suppression of STT post dacryoadenectomy did not occur in our model. Failure to completely ablate all tear production with lacrimal gland removal is not surprising and has been documented in multiple other species including mice,46 rat,47 rabbits,48 squirrel monkey,13 and even humans.49 Although the complete removal of all LG tissue in most of these reports is unlikely, the definitive source of this residual tear production remains elusive. In our model, careful anatomic dissection at necropsy showed tear production was not due to regrowth of any LG tissues. Other possible sources for the residual tear fluid include the largely untouched accessory LGs, fluid from other conjunctival sources and plasma leakage from conjunctival vessels.50–52 Previous works have provided evidence that conjunctival and/or corneal tissues have the ability to secrete or transport fluid into the tear film.48,51,53,54 Changes in aquaporin expression and/or function may underlie some of the residual tear production.15 Harder’s gland is an unlikely source as it produces a small amount of a predominantly lipid-based emulsion.35,55 Because our simple and safe surgical method completely ablates all of the orbital LG tissues, our model provides an excellent means to study the in vivo compensatory mechanisms of the conjunctival and corneal tissues in a setting of aqueous deficient DED.