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Water Homeostasis (water + homeostasi)
Selected AbstractsAquaporin 4 changes in rat brain with severe hydrocephalusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2006Xiaoyan Mao Abstract Hydrocephalus is characterized by impaired cerebrospinal fluid (CSF) flow with enlargement of the ventricular cavities of the brain and progressive damage to surrounding tissue. Bulk water movement is altered in these brains. We hypothesized that increased expression of aquaporins, which are water-permeable channel proteins, would occur in these brains to facilitate water shifts. We used quantitative (real-time) RT-PCR, Western blotting and immunohistochemistry to evaluate the brain expression of aquaporins (AQP) 1, 4, and 9 mRNA and protein in Sprague,Dawley rats rendered hydrocephalic by injection of kaolin into cistern magna. AQP4 mRNA was significantly up-regulated in parietal cerebrum and hippocampus 4 weeks and 9 months after induction of hydrocephalus (P < 0.05). Although Western blot analysis showed no significant change, there was more intense perivascular AQP4 immunoreactivity in cerebrum of hydrocephalic brains at 3,4 weeks after induction. We did not detect mRNA or protein changes in AQP1 (located in choroid plexus) or AQP9 (located in select neuron populations). Kir4.1, a potassium channel protein linked to water flux, exhibited enhanced immunoreactivity in the cerebral cortex of hydrocephalic rats; the perineuronal distribution was entirely different from that of AQP4. These results suggest that brain AQP4 up-regulation might be a compensatory response to maintain water homeostasis in hydrocephalus. [source] p.R254Q mutation in the aquaporin-2 water channel causing dominant nephrogenic diabetes insipidus is due to a lack of arginine vasopressin-induced phosphorylation,HUMAN MUTATION, Issue 10 2009Paul JM Savelkoul Abstract Vasopressin regulates human water homeostasis by re-distributing homotetrameric aquaporin-2 (AQP2) water channels from intracellular vesicles to the apical membrane of renal principal cells, a process in which phosphorylation of AQP2 at S256 by cAMP-dependent protein kinase A (PKA) is thought to be essential. Dominant nephrogenic diabetes insipidus (NDI), a disease in which the kidney is unable to concentrate urine in response to vasopressin, is caused by AQP2 gene mutations. Here, we investigated a reported patient case of dominant NDI caused by a novel p.R254Q mutation. Expressed in oocytes, AQP2-p.R254Q appeared to be a functional water channel, but was impaired in its transport to the cell surface to the same degree as AQP2-p.S256A, which mimics non-phosphorylated AQP2. In polarized MDCK cells, AQP2-p.R254Q was retained and was distributed similarly to that of unstimulated wt-AQP2 or AQP2-p.S256A. Upon co-expression, AQP2-p.R254Q interacted with, and retained wt-AQP2 in intracellular vesicles. In contrast to wild-type AQP2, forskolin did not increase AQP2-p.R254Q phosphorylation at S256 or its translocation to the apical membrane. Mimicking constitutive phosphorylation in AQP2-p.R254Q with the p.S256D mutation, however, rescued its apical membrane expression. These date indicate that a lack of S256 phosphorylation is the sole cause of dominant NDI here, and thereby, p.R254Q is a loss of function instead of a gain of function mutation in dominant NDI. © 2009 Wiley-Liss, Inc. [source] Chronic constriction injury induces aquaporin-2 expression in the dorsal root ganglia of ratsJOURNAL OF ANATOMY, Issue 5 2009Barbara Buffoli Abstract Aquaporins are a family of water channel proteins involved in water homeostasis in several tissues. Current knowledge of aquaporin expression in the nervous system is very limited. Therefore the first aim of this study was to assess, by immunohistochemistry and immunoblotting analysis, the presence and localization of aquaporin-2 in the spinal cord and dorsal root ganglia of naïve adult rats. In addition, we evaluated aquaporin-2 expression in response to chronic constriction injury of the sciatic nerve, a model of neuropathic pain. Our results showed that aquaporin-2 expression was not detectable either in the spinal cord or the dorsal root ganglia of naïve rats. However, we showed for the first time an increase of aquaporin-2 expression in response to chronic constriction injury treatment in small-diameter dorsal root ganglia neurons but no expression in the lumbar spinal cord. These data support the hypothesis that aquaporin-2 expression is involved in inflammatory neuropathic nerve injuries, although its precise role remains to be determined. [source] Liver disease and the renin,angiotensin system: Recent discoveries and clinical implicationsJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 9 2008John S Lubel Abstract The renin,angiotensin system (RAS) is a key regulator of vascular resistance, sodium and water homeostasis and the response to tissue injury. Historically, angiotensin II (Ang II) was thought to be the primary effector peptide of this system. Ang II is produced predominantly by the effect of angiotensin converting enzyme (ACE) on angiotensin I (Ang I). Ang II acts mainly through the angiotensin II type-1 receptor (AT1) and, together with ACE, these components represent the ,classical' axis of the RAS. Drug therapies targeting the RAS by inhibiting Ang II formation (ACE inhibitors) or binding to its receptor (angiotensin receptor blockers) are now in widespread clinical use and have been shown to reduce tissue injury and fibrosis in cardiac and renal disease independently of their effects on blood pressure. In 2000, two groups using different methodologies identified a homolog of ACE, called ACE2, which cleaves Ang II to form the biologically active heptapeptide, Ang-(1,7). Conceptually, ACE2, Ang-(1,7), and its putative receptor, the mas receptor represent an ,alternative' axis of the RAS capable of opposing the often deleterious actions of Ang II. Interestingly, ACE inhibitors and angiotensin receptor blockers increase Ang-(1,7) production and it has been proposed that some of the beneficial effects of these drugs are mediated through upregulation of Ang-(1,7) rather than inhibition of Ang II production or receptor binding. The present review focuses on the novel components and pathways of the RAS with particular reference to their potential contribution towards the pathophysiology of liver disease. [source] Der Epitheliale Natrium Kanal.BIOLOGIE IN UNSERER ZEIT (BIUZ), Issue 5 200915 Jahre Kanalarbeiten Abstract Epitheliale Natrium Kanäle (ENaCs) sind Natrium leitende Ionenkanäle, die in der apikalen Membran vieler Epithelien vorkommen. Sie sind der zentrale Faktor zum transepithelialen Transport von Natrium , und damit einhergehend von Wasser. ENaCs tragen zu einer Vielzahl physiologischer Prozesse bei: Regulation des Salz- und Wasserhaushalts, des Blutdrucks oder des Wassergehaltes der Lunge. Auch Erkrankungen wie Bluthochdruck oder Lungenödeme lassen sich auf gestörte Regulationen des ENaC zurückführen. Dieser Artikel beschreibt die Funktion und Physiologie Epithelialer Natrium Kanäle, sowie zelluläre Mechanismen, die die Aktivität dieser Ionenkanäle bestimmen. Epithelial sodium channels (ENaCs) are sodium-conducting ion channels that are located in the apical membrane of various epithelia. They represent the rate-limiting step for transeptihelial sodium- and thereby water-transport. ENaCs contribute to a variety of physiological processes including the regulation of salt and water homeostasis, blood pressure or the water content of the lung. Further, malfunctions in ENaC regulation contribute to the pathogenesis of diseases like hypertension or pulmonary oedema. This article describes the function and physiology of epithelial sodium channels as well as cellular mechanisms that determine the activity of these ion channels. [source] TRANSLATIONAL RESEARCH GOES BOTH WAYS: LESSONS FROM CLINICAL STUDIESCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2008John W Funder SUMMARY 1It is currently assumed that translational research goes from benchtop to bedside; that aldosterone elevates blood pressure via its effects on salt and water homeostasis; that mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) share a common immediate ancestor; and that aldosterone plays a deleterious role in essential hypertension and heart failure. 2Meta-analysis of clinical trials in essential hypertension, in which eplerenone was dose-titrated to attain diastolic blood pressure < 90 mmHg, showed no relationship between blood pressure response and electrolyte effects, as judged by change in plasma (K). 3Reexamination of sequence data, and insights from the S810L MR mutant gene causing juvenile hypertension exacerbated by pregnancy, suggest that MR were the first to branch off the primordial ancestor for MR, GR, androgen receptors (AR) and progesterone receptors (PR). 4In clinical trials of MR blockade in heart failure and essential hypertension baseline aldosterone levels are in the low to normal range and sodium status unremarkable. Under such circumstances cortisol appears to be responsible for MR activation, thus exculpating aldosterone in these conditions. 5On the basis of these clinical studies, there is need to revisit the basic biology of aldosterone and MR as translational research very clearly goes both ways. [source] | |||||||||||||