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At least 127 records · Page 7Linked to original sources
PubMed2004

Localised mapping of water movement and hydration inside a developing bioadhesive bond.

Few studies have investigated the internal processes involved in bioadhesive bond formation, particularly where mucus and hydrated polymer contribute jointly to bond structure. This paper reports the first study to spatially map the internal environment within a developing bioadhesive bond, utilising nuclear magnetic resonance (NMR) microscopy to measure localised water self-diffusion coefficients (SDC) and confocal laser scanning microscopy (CLSM) to estimate mucin concentration. In a model bioadhesive bond formed between an alginate matrix and mucin gel, characteristic profiles were observed in which fluorescence measurements showed a region of increasing mucin concentration in the mucus layer region adjacent to the matrix, corresponding closely with a zone of restricted water SDC in the diffusion profiles. These regions extended 144 microm (a normal human gastric layer thickness [Clin. Sci. 95 (1998) 97]) into the mucin layer after just 30 s, increasing to 800 microm after 30 min. The formation of a hydrated polymer layer at the matrix surface, confirmed visually, was also reflected in corresponding gradient changes. The results suggest a progressive dehydration of the mucus gel during bond formation, and the study demonstrates how together, these microscopies can provide non-invasive, quantitative, spatial and time-resolved evidence of internal hydration behaviour during bioadhesive bond formation.

Adhesiveness↗
PubMed2002

Channel-mediated water movement across enclosed or perfused mouse intrahepatic bile duct units.

We previously reported the development of reproducible techniques for isolating and perfusing intact intrahepatic bile duct units (IBDUs) from rats. Given the advantages of transgenic and knockout mice for exploring ductal bile formation, we report here the adaptation of those techniques to mice and their initial application to the study of water transport across mouse intrahepatic biliary epithelia. IBDUs were isolated from livers of normal mice by microdissection combined with enzymatic digestion. After culture, isolated IBDUs sealed to form intact, polarized compartments, and a microperfusion system employing those isolated IBDUs developed. A quantitative image analysis technique was used to observe a rapid increase of luminal area when sealed IBDUs were exposed to a series of inward osmotic gradients reflecting net water secretion; the choleretic agonists secretin and forskolin also induced water secretion into IBDUs. The increase of IBDU luminal area induced by inward osmotic gradients and choleretic agonists was reversibly inhibited by HgCl2, a water channel inhibitor. With the use of a quantitative epifluorescence technique in perfused mouse IBDUs, a high osmotic water permeability (P(f) = 2.5-5.6 x 10(-2) cm/s) was found in response to osmotic gradients, further supporting the presence of water channels. These findings suggest that, as in the rat, water transport across intrahepatic biliary epithelia in mice is water channel mediated.

Animals↗
PubMed1977

Water movement between myocardial tissue and capillary blood during and after coronary reactive hyperemia as studied by continuous measurement of colloid osmotic pressure of cardiac venous blood.

Colloid osmotic pressure (COP) of blood from the great cardiac vein was continuously measured by the use of a membrane colloid osmometer during reactive hyperemia resulting from temporary occlusion of the anterior descending branch of left coronary artery. The COP increased sharply but transit was concluded that a measurable amount of water moved from the capillary blood into the myocardial tissue and then flowed back slowly into the capillary blood.

Animals↗
PubMed1996

Main intrinsic polypeptide and water movement--recent developments and future prospects.

Age-related lens opacity is the major cause of loss of vision affecting more than half of the world's blind. The development of cataract is associated with changes in the structure of the lens. The lens consists largely of closely packed fibre cells forming a transparent syncytium. The main intrinsic polypeptide (MIP) of the lens fibre cells forms 40% of the fibre membrane, and forms a system of membrane channels. The precise structure and function of these channels remains obscure, although their role as large water-filled channels has been suggested in maintenance of structural integrity as well as their role in transport of nutrients. MIP is a member of a large family of channels of common ancestry. Some of the most recent studies of structure and function of this family have been carried out on CHIP (a water channel found in red blood cells) which is a member of this family closely related to MIP. Both CHIP and MIP m-RNA's have been expressed in oocyte membranes, and water permeabilities per channel have been measured. Surprisingly, CHIP and MIP channels have high and low water permeabilities, respectively. This is discussed in terms of recent high resolution structure determinations, the lens fibre MIP function, and future studies.

Animals↗
PubMed1996

pH-dependent structural changes in the active site of p-hydroxybenzoate hydroxylase point to the importance of proton and water movements during catalysis.

Deprotonation of p-hydroxybenzoate to the phenolate and reprotonation of the hydroxylated dienone intermediate to form the product are essential steps in the reaction catalyzed by p-hydroxybenzoate hydroxylase (PHBH). The mechanism by which protons are transferred in these reactions is not obvious, because the substrate bound in the active site is isolated from solvent. Structure analyses of wild-type and mutant PHBH, with bound p-hydroxybenzoate or p-aminobenzoate, reveal a chain of proton donors and acceptors (the hydroxyl groups of Tyr201 and Tyr385, and two water molecules) that can connect the substrate 4-OH to His72, a surface residue. This chain could provide a pathway for proton transfer to and from the substrate. Using various combinations of pH and substrates, we show that in crystalline PHBH ionizable groups in the chain may rotate and change hydrogen-bond orientation. Molecular dynamics simulations have been used to predict the preferred orientation of hydrogen bonds in the chain as a function of the ionization states of substrate and His72. The calculations suggest that changes in the ionization state of the substrate could be associated with changes in orientation of the hydrogen bonds in the chain. Transfer of water between the chain of proton donors and the solvent also appears to be an essential part of the mechanism that provides reversible transfer of protons during the hydroxylation reaction.

4-Hydroxybenzoate-3-Monooxygenase↗