Items in TSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Abstract summary : Introduction. All the living organisms are made principally of water, which is fundamental to the cell homeostasis to all levels. For this reason water transport through biological membranes has ever been a very interesting field in physiology.
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Aquaporins AQPs are members of the aquaporin water channel family that play an important role in reabsorption of water from the renal tubular fluid to concentrate urine. The renal medulla of cattle Bos taurus acted as the control.
Compared with the control, strong expression of AQP2 was observed at the apical plasma membrane and intracellular vesicles, in both the outer medullary collecting duct OMCD and the inner medullary collecting duct IMCD of camel. It may enhance our better understanding of special water metabolism mechanisms that enable camels to survive in extreme environments.
Bactrian camels serve as a very important part in the production of agriculture and the development of animal husbandry in those regions. To adapt to the harsh conditionshot and arid of deserts or semi-deserts, camels acquire a number of special characteristics.
Blood glucose levels in camels are twice those of other ruminants Al-Ali et al. Camels tolerate a high dietary intake of salt, consuming eight times more than cattle and sheep Food and Agriculture Organization of the United Nations, Aquaporins AQPs are a family of small, approximately 30 kDa integral membrane proteins that act as water channels.
AQPs are responsible for facilitated transmembrane water transport in a variety of epithelial and nonepithelial cells Huang et al. In mammals, 13 AQP subtypes, named AQP, have been identified and these are expressed in various tissues such as the kidney, brain, liver, lungs and salivary glands Ishibashi et al. Eight isoforms of AQPs , , 11 are expressed in the kidney of which five have been shown to play a role in body water balance. To our knowledge, ours is the first report that shows AQPs expression in the renal medulla of Bactrian camels.
We believe that AQPs expression and water transport in the kidney of camels in deserts or semi-deserts zone differ from other species for reduction of renal fluid loss and maintenance of body fluid balance. It has been reported that AQP2 is regulated both in trafficking short-term regulation and in abundance long-term regulation via arginine vasopressin AVP Nielsen et al. The kidneys belonging to healthy Bactrian camels 4 castrated years old were collected immediately after slaughter from a slaughter house of the Right Alasan Banner Food Company in Inner Mongolia Autonomous Region, China.
For comparison, the kidneys of healthy cattle Bos taurus; 4 castrated, years old were collected immediately after slaughter from a slaughter house of Linxia Hui autonomous prefecture, Gansu Province, China. For immunolight microscopy, specimens were dehydrated through a graded series of alcohol, cleared and embedded in paraffin wax, and sectioned at 5mm used for immunohistochemical staining. The sections were dewaxed and rehydrated, an antigen retrieval procedure was performed to unmask antigens, by treating the samples three times in a microwave oven at medium-high fire for 5 min each time in 10 mM citrate buffer, pH 6.
The primary antibody was diluted in 10 mM PBS supplemented with 0. Counterstaining was with hematoxylin staining. Counterstaining with hematoxylin staining was used to identify negative segments. In this study, renal medulla was divided into the outer and inner medulla, for collecting duct, thereby forming the outer medullary collecting duct OMCD and the inner medullary collecting duct IMCD.
It was observed different AQP4 expression in medulla between the control cattle and camel. Moreover, moderate AQP4 expression was detected in endothelium of capillary in medullary region of camels Fig.
Cattle and pig are the closest relatives of Bacterian camels, which belong to artiodactyla even-toed ungulates in taxonomy Bactrian Camels Genome Sequencing and Analysis Consortium et al. That is why cattle were acted as the control in this study. The results are in agreement with our expectation. AQP2 has been reported to occur in the principal cells along connecting tubule and collecting duct in mammalian kidneys, where it is localized to the apical plasma membranes and intracellular membrane vesicles Nielsen et al.
The transcellular route of regulation mainly occurs via modulating cell surface expression of AQP2. AVP binds to the vasopressin type-2 receptor V2R , present in the basolateral membrane of renal collecting duct principal cells and connecting tubule cells Fenton et al.
The overall process results in a concentration of the urine. Comparing with the control, we observed strong AQP2 expression at the apical cell membrane in the IMCD and OMCD of camels, it may be result of long-term V2R stimulation, which was consistent with the high water permeability of collecting duct, thereby camels can produce highly concentrated urine.
However, the specific function and mechanisms of this observation is not clear and this issue should be investigated further. It has been suggested that AQP3 and AQP4 are localized in the basolateral membrane of principal cells of the collecting duct and will normally produce a net flow of water into the interstitium Ecelbarger et al.
AQP3 has been shown to be important for the urine concentrating mechanism, as AQP3 knockout mice have an increased urine volume, lower urine osmolality and a reduced osmotic water permeability of the basolateral membrane of the collecting duct Ma et al. We speculated whether there was a innate regulatory mechanism in water reabsorption for camels as above Namely, more AVP has been secreted in the hypothalamus since long-term adaptation to drought, than AVP combined with V2R and induced a series of signaling cascade; eventually lead to upregulation of aquaporin proteins in renal inner medulla and outer medulla, thereby enhancing water reabsorption and effectively reserving water of body.
This result of observation in this paper is basically consistent with our speculation, however, further research on specific mechanisms is still needed. Driven by the transcellular osmotic gradient, water then will enter principal cells through AQP2 and enters the blood via AQP3 and AQP4 water channels, which are expressed in the basolateral membrane, resulting in concentrated urine Ishibashi et al.
It is suggested that this observation maybe explain water entering the blood via AQP4 water channels in the endothelium.
To adapt to the harsh conditions of hot and arid deserts or semi-deserts, camels tolerate a high dietary intake of salt and can produce highly concentrated urine. AQPs may play a key role in body water balance, thereby maintaining water homeostasis. Our findings may also improve our understanding of special water metabolism mechanisms that enable camels to survive in extreme environments. In addition, it is important to study other AQPs in the camel kidney to better understand the exact functions in water reabsorption.
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O mecanismo do transporte facilitado de auga e a probable existencia de poros acuosos interesou aos investigadores desde A presenza de canles de auga incrementa a permeabilidade de membrana para a auga. Na Galipedia, a Wikipedia en galego. Xunta de Galicia. Proc Am Thorac Soc 3 1 : 5—
2012, Número 1
Aquaporins AQPs are members of the aquaporin water channel family that play an important role in reabsorption of water from the renal tubular fluid to concentrate urine. The renal medulla of cattle Bos taurus acted as the control. Compared with the control, strong expression of AQP2 was observed at the apical plasma membrane and intracellular vesicles, in both the outer medullary collecting duct OMCD and the inner medullary collecting duct IMCD of camel. It may enhance our better understanding of special water metabolism mechanisms that enable camels to survive in extreme environments. Bactrian camels serve as a very important part in the production of agriculture and the development of animal husbandry in those regions. To adapt to the harsh conditionshot and arid of deserts or semi-deserts, camels acquire a number of special characteristics. Blood glucose levels in camels are twice those of other ruminants Al-Ali et al.
Aquaporins , also called water channels , are integral membrane proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells , mainly facilitating transport of water between cells. Two hydrophobic loops contain conserved asparagine-proline-alanine NPA motif which form a barrel surrounding a central pore-like region that contains additional protein density. Water can pass through the cell membrane through simple diffusion because it is a small molecule, and through osmosis , in cases where the concentration of water outside of the cell is greater than that of the inside. However, because water is a polar molecule this process of simple diffusion is relatively slow, and the majority of water passes through aquaporin. The Nobel Prize in Chemistry was awarded jointly to Peter Agre for the discovery of aquaporins  and Roderick MacKinnon for his work on the structure and mechanism of potassium channels. Genetic defects involving aquaporin genes have been associated with several human diseases including nephrogenic diabetes insipidus and neuromyelitis optica. The mechanism of facilitated water transport and the probable existence of water pores has attracted researchers since