Glucose Permeability Research Articles

Collagen–phosphorylcholine interpenetrating network hydrogels as corneal substitutes

A biointeractive collagen–phospholipid corneal substitute was fabricated from interpenetrating polymeric networks comprising 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide and N-hydroxysuccinimide crosslinked porcine atelocollagen, and poly(ethylene glycol) diacrylate crosslinked 2-methacryloyloxyethyl phosphorylcholine (MPC). The resulting hydrogels showed an overall increase in mechanical strength beyond that of either original component and enhanced stability against enzymatic digestion (by collagenase) or UV degradation. More strikingly, these hydrogels retained the full biointeractive, cell friendly properties of collagen in promoting corneal cell and nerve in-growth and regeneration (despite MPC's known anti-adhesive properties). Measurements of refractive indices, white light transmission and backscatter showed the optical properties of collagen–MPC are comparable or superior to those of the human cornea. In addition, the glucose and albumin permeability were comparable to those of human corneas. Twelve-month post-implantation results of collagen–MPC hydrogels into mini-pigs showed regeneration of corneal tissue (epithelium, stroma) as well as the tear film and sensory nerves. We also show that porcine collagen can be substituted with recombinant human collagen, resulting in a fully-synthetic implant that is free from the potential risks of disease transmission (e.g. prions) present in animal source materials.

Thermoplastic amphiphilic conetworks

Our main objective was the design, synthesis, characterization, and testing of a novel class of materials, thermoplastic amphiphilic conetworks (TP-APCNs). A further objective was the evaluation of TP-APCNs as biomaterials, for example, as immunoisolatory membranes in a bioartificial pancreas, or as extended-wear soft contact lenses. The synthesis of the first TP-APCNs was accomplished by blending an amphiphilic graft polymer, poly(dimethyl acryl amide)-g-polydimethylsiloxane (PDMAAm-g-PDMS), with a commercial PDMS-containing polyurethane (PU). The common PDMS segments coalesce and form a single phase, whereas the hard/crystalline segments of the PU physically crosslink the blend. The properties of TP-APCNs can be controlled by the graft/PU ratio and segment molecular weights. TP-APCNs with cocontinuous hydrophilic and hydrophobic phases were prepared as demonstrated by swelling in water and n-heptane. Depending on the blend ratio and molecular weights, optically clear water-swollen TP-APCNs with 0.5–4 MPa tensile strength, 70–280% elongation, together with 2–11 × 10−7 cm2/s glucose permeability, and 1.2–8 × 10−8 cm2/s insulin permeability were prepared. TP-APCNs are processible by casting and molding. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 682–691, 2009

A novel macroencapsulating immunoisolatory device: the preparation and properties of nanomat-reinforced amphiphilic co-networks deposited on perforated metal scaffold

This paper describes the design and preparation of the non-biological components (the "hardware") of a conceptually novel bioartificial pancreas (BAP) to correct diabetes. The key components of the hardware are (1) a thin (5-10 microm) semipermeable amphiphilic co-network (APCN) membrane [i.e., a membrane of cocontinuous poly(dimethyl acryl amide) (PDMAAm)/polydimethylsiloxane (PDMS) domains cross-linked by polymethylhydrosiloxane (PMHS)] expressly created for macroencapsulation and immunoisolation of a tissue graft; (2) an electrospun nanomat of PDMS-containing polyurethane to reinforce the water-swollen APCN membrane; and (3) a perforated hollow-ribbon nitinol scaffold to stiffen and provide geometric stability to the construct. The reinforcement of water-swollen hydrogels with an electrospun nanomat is a generally applicable new method for hydrogel reinforcement. Details of device design and preparation are discussed. The advantages and disadvantages of micro- and macro-immunoisolation are analyzed, and the requirements for the ideal immunoisolatory membrane are presented. Burst pressure, and glucose and insulin permeabilities of representative devices have been determined and the effect of device composition and wall thickness on these properties is discussed.

Preparation and properties of a chitosan-based carrier of corneal endothelial cells

A novel chitosan-based membrane that was made of hydroxypropyl chitosan, gelatin and chondroitin sulfate was used as a carrier of corneal endothelial cells. The characteristics of the blend membrane, such as transparency, equilibrium water content, permeability, mechanical properties, protein absorption ability, hydrophilicity and surface morphology, were determined. To study the effects of the membrane on cell attachment and growth, rabbit corneal endothelial cells were cultured on this artificial membrane. The biodegradability and biocompatibility of the blend membrane were in vivo evaluated by its implantation into the muscle of the rats. Glucose permeation results demonstrated that the blend membrane had higher glucose permeability than natural human cornea. Scanning electron microscopy (SEM) analysis of the membranes demonstrated that no fibrils were observed. As a result, the optical transparency of the membrane was as good as the natural human cornea. The average value of tensile strength of the membrane was 13.71 MPa for dry membrane and 1.48 MPa for wet membrane. The value of elongation at break of the wet was 45.64%. The cultured rabbit corneal endothelial cells formed a monolayer on the blend membrane which demonstrated that the membrane was suitable for corneal endothelial cells to attach and grow. In addition, the membranes in vivo showed a good bioabsorption property. The mild symptoms of inflammation at sites of treatment could be resolved as the implant was absorbed by the host. The results of this study demonstrated that the hydroxypropyl chitosan-chondroitin sulfate-gelatin blend membrane can potentially be used as a carrier for corneal endothelial cell transplantation.

Osmotic Water Transport with Glucose in GLUT2 and SGLT

Carrier-mediated water cotransport is currently a favored explanation for water movement against an osmotic gradient. The vestibule within the central pore of Na+-dependent cotransporters or GLUT2 provides the necessary precondition for an osmotic mechanism, explaining this phenomenon without carriers. Simulating equilibrative glucose inflow via the narrow external orifice of GLUT2 raises vestibular tonicity relative to the external solution. Vestibular hypertonicity causes osmotic water inflow, which raises vestibular hydrostatic pressure and forces water, salt, and glucose into the outer cytosolic layer via its wide endofacial exit. Glucose uptake via GLUT2 also raises oocyte tonicity. Glucose exit from preloaded cells depletes the vestibule of glucose, making it hypotonic and thereby inducing water efflux. Inhibiting glucose exit with phloretin reestablishes vestibular hypertonicity, as it reequilibrates with the cytosolic glucose and net water inflow recommences. Simulated Na+-glucose cotransport demonstrates that active glucose accumulation within the vestibule generates water flows simultaneously with the onset of glucose flow and before any flow external to the transporter caused by hypertonicity in the outer cytosolic layers. The molar ratio of water/glucose flow is seen now to relate to the ratio of hydraulic and glucose permeability rather than to water storage capacity of putative water carriers.

Liquid Crystal Membranes for Serum-Compatible Diabetes Management-Assisting Subcutaneously Implanted Amperometric Glucose Sensors

Membranes formed of thermodynamically stable cubic phase lyotropic liquid crystals (LLCs) could replace the presently used polymeric membranes, applied to reduce the flux of glucose in semicontinuous, subcutaneously implanted, user-replaced, miniature, amperometric glucose sensors, assisting in the management of diabetes. LLC-forming amphiphilic compounds set and toughen spontaneously after mixing with water, without undergoing chemical change. When applied by doctor-blading, they form membranes having three-dimensionally interconnected water channels of uniform diameter, with reproducible glucose transport-characteristics. We find that the best studied cubic phase LLCs, which are formed of monoolein and water, are not useful in their intended application because they are hydrolyzed by serum lipases. Those formed of phytantriol, a liquid at ambient temperature, and water, are not hydrolyzed but change their shape and size in a dehydration and rehydration cycle. Because glucose sensors are sterilized and stored in a sealed package in a dry atmosphere, drying and rehydration must not change the transport characteristics. A third, novel, LLC-forming, amphiphile 1-O-beta-(3,7,11,15-tetramethylhexadecyl)-d-ribopyranoside, I, was synthesized, and its phase diagram was tailored by adding Vitamin E acetate, to form a cubic phase. The phase was stable through the 20 degrees C-90 degrees C temperature range in excess of water and had the desired glucose-transport characteristics. A preferred LLC, II, was formed of water and I containing 7 wt % of Vitamin E acetate. When II was applied to a wired glucose oxidase bioelectrocatalyst, sensors of reproducible glucose-sensitivity were formed. At a 0.1 mm thickness of II, the membrane reduced the glucose flux 5-fold and increased the 90% response-time by less than 2 min. The membrane was mechanically rugged, withstanding the approximately 1 N m(-2) maximal shear stress at 5 mm diameter electrodes rotating at 4000 rpm. The activation energy for glucose permeation through II was reduced to 15.6 kJ/mol, making the sensors's current less temperature-dependent than that of the polymeric-membrane overcoated implantable glucose sensors.

Effect of pancragen on blood glucose level, capillary permeability and adhesion in rats with experimental diabetes mellitus

The effects of tetrapeptide pancragen (Lys-Glu-Asp-Trp-NH2) on blood glucose level and permeability and adhesion of mesenteric capillaries were studied in Wistar rats with experimental streptozotocin-induced diabetes mellitus. Oral pancragen produced a pronounced hypoglycemic effect during treatment. Intramuscular pancragen normalized the adhesion of mesenteric capillary endothelium, but did not modify capillary permeability. The results indicate homeostatic and endothelioprotective effects of pancragen during the early period of diabetes mellitus.

Third‐generation amphiphilic conetworks. III. Permeabilities and mechanical properties

AbstractWhile two of our earlier papers on poly(dimethyl acryl amide)/polymethylhydrosiloxane/polydimethylsiloxane (PDMAAm/PMHS/PDMS) amphiphilic conetworks concerned synthesis and biological properties, respectively, the present contribution focuses on oxygen and insulin permeabilities, and select mechanical properties. We show that by increasing the PDMAAm content from 20 to 60% (i.e., by decreasing the hydrophobic content from 80 to 40%), oxygen permeabilities decrease from ∼240 to ∼130 barrers. Evidently, oxygen permeability is a function of the sum of the oxyphilic components, PDMS + PMHS, in the conetworks. In contrast, insulin permeability is a function of the hydrophilic component, and reaches a desirable 1.5 × 10−7 cm2/s at 61% PDMAAm. We also studied the permeabilities of glucose, dextran, and albumin through a PDMAAm61/PMHS6/PDMS33 membrane and found, unsurprisingly, that the permeability of these molecules follows their hydrodynamic radii, and we project that the permeability of IgG is infinitesimally low. Tensile strengths and ultimate elongations of water‐swollen membranes are also a function of conetwork composition: by increasing the PDMAAm content from 30 to 60%, strengths decrease from 1.6 to 1.2 MPa, and elongations from ∼60 to ∼40%. Overall, the permeabilities and the mechanical properties of these membranes are appropriate for implantation and, specifically, for immunoisolation of living tissue. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4276–4283, 2007

On-Chip Microdialysis System with Flow-Through Glucose Sensing Capabilities

Microdialysis is a sampling technique based on controlling the mass transfer rate of different-sized molecules across a semipermeable membrane. Because the dialysis process has minimal effects on the surrounding fluid, it is viewed as a tool for continuous monitoring of human metabolites. In diabetes treatment, microdialysis probes have been used as sampling systems coupled to a glucose biosensor but may struggle to obtain high recoveries of analytes, as the sampling housing, probes, and glucose sensors are fabricated as separate pieces and then assembled, resulting in a large dead volume, which limits sensing frequency. An in situ combination of a miniaturized microdialysis probe with an integrated glucose sensor could help solve some of these problems. The system was fabricated by bonding a 6-mum-thick polycarbonate track-etch membrane with 100-nm-diameter pores onto microfluidic channels with the electrochemical glucose sensing electrodes patterned within the microchannels. In vitro experiments demonstrating glucose microdialysis with continuous sensing were conducted. The permeability of glucose to the polycarbonate membrane with a 100-nm-diameter pore size was obtained to be 5.44 mum/s. Glucose recovery of 99% was observed using this microdialysis system at a perfusion flow rate of 0.5 microl/min. Experiments monitoring fluctuating glucose concentrations in the time domain at 99% recovery were also performed. The lag time was measured to be 210 seconds with 45 seconds contributed by mass transfer limitations and the rest from dead volume within the experimental setup. The electrochemical sensing component was able to continuously track concentration changes in the reservoir. This system is expected to have the proper sensitivity to track physiologically relevant concentration changes of glucose with a lag time of less than 1 minute and minimal amplitude reduction for continuous glucose monitoring for diabetes treatment.

Glycated haemoglobin (HbG) as a stable indicator of blood glucose status in ostrich

Glycated haemoglobin (HbG) concentration is a retrospective measure of mean blood glucose level and is not affected by recent stresses, food ingestion or exercise. HbG has been determined in various wild and domestic animals such as kestrels, mankhor, mouflon, aoudad, deer, goat, sheep, dog, camel and horse. But there is no information regarding HbG in ostrich and its relation to blood glucose. The purposes of this study were to determine the normal values of HbG in ostriches and to investigate its relation to fasting plasma glucose. Blood samples were collected from jugular veins of 30 clinically healthy ostriches after 12 h of fasting. After separation and washing of red blood cells, haemolysate was prepared and subjected to weak cation exchange chromatography for determination of HbG. Glucose was measured in plasma samples. Fasting plasma glucose and HbG were 11.23 ± 0.80 mmol/l and 1.20 ± 0.2% of total haemoglobin, respectively. It was shown that HbG percent and fasting plasma glucose were correlated (P < 0.05; r = 0.93). To determine if low HbG percent in ostrich is related to low permeability of erythrocytes to blood glucose, haemolysates incubated with glucose (11.21 mmol/l final glucose concentrations) were subjected to chromatography under the same conditions. It was shown that HbG was significantly increased in glycosylated haemolysates. It was concluded that low HbG percent in ostrich is related to low glucose permeability of erythrocytes.

Radiosynthesis of hydrogel confined to hollow-fiber membranes for the design of a bioartificial extra-corporeal liver

Current bioartificial extra-corporeal systems are bioreactors where cells are separated from the surrounding media by porous polymeric membranes. The present work focuses on the design of membranes that allow the differential diffusion of plasma metabolites and proteins such as immunoglobulin (IgG). This design will improve catabolites removal and reduce possible immune response and virus infection. We demonstrate the feasibility to synthesize the hydrogels confined to the macroporous structure of membranes by radiation-induced in situ polymerization. The hollow-fiber membranes were soaked in aqueous monomeric solution, rinsed and irradiated while submerged in oil. This procedure confined the hydrogel to the void internal volume of the pores of the membrane. Hydrogels of polyacrylamide and polyHEMA were synthesized this way by irradiation at 10 kGy. Hydraulic permeability and diffusion of glucose, albumin and IgG were measured in these hydrogel-filled membranes. Polyacrylamide 0.5 M showed the best compromise between albumin diffusion (1.2×10 −7 cm 2/s) and HSA/IgG selectivity (2.2).

A highly conserved hydrophobic motif in the exofacial vestibule of fructose transporting SLC2A proteins acts as a critical determinant of their substrate selectivity

The substrate specificity of the facilitated hexose transporter, GLUT, family, (gene SLC2A) is highly varied. Some appear to be able to translocate both glucose and fructose, while the ability to handle 2-deoxyglucose and galactose does not necessarily correlate with the other two hexoses. It has become generally accepted that a central substrate binding/translocation site determines which hexoses can be transported. However, a recent study showed that a single point mutation of a hydrophobic residue in GLUTs 2, 5 & 7 removed their ability to transport fructose without affecting the kinetics of glucose permeation. This residue is in the 7th transmembrane helix, facing the aqueous pore and lies close to the opening of the exofacial vestibule. This study expands these observations to include the other class II GLUTs (9 & 11) and shows that a three amino acid motif (NXI/NXV) appears to be critical in determining if fructose can access the translocation mechanism. GLUT11 can also transport fructose, but it has the motif DSV at the same position, which appears to function in the same manner as NXI and when all three residues are replaced with NAV fructose transport lost. These results are discussed in relation to possible roles for hydrophobic residues lining the aqueous pore at the opening of the exofacial vestibule. Finally, the possibility that the translocation binding site may not be the sole determinant of substrate specificity for these proteins is examined.

Glucose Recovery with Bare and Hydrogel-Coated Microdialysis Probes: Experiment and Simulation of Temporal Effects

In vitro microdialysis glucose sampling was used to test the transient and steady-state suitability of antifouling hydrogel coatings, composed of 2-hydroxyethyl methacrylate, vinylpyrrolidinone, and poly(ethylene glycol). The in vitro glucose diffusion coefficients of bare microdialysis membranes and hydrogel coatings were determined experimentally to be 1.1 x 10-6 and 3.2 x 10-6 cm2/s, respectively. These values were used to numerically simulate the effect of the hydrogel on glucose transport across the microdialysis membrane using a convection-diffusion transport model. The times for dialysate at the exit of the bare and hydrogel-coated microdialysis probes to reach 95% of steady state were calculated to be 20 and 66 s, respectively. However, the experimental data showed that 95% of steady-state glucose recoveries were reached after 4-5 min. Numerical simulations incorporating the Taylor dispersion in the outlet tubing showed the time difference was caused almost completely by convective transport in the outlet tubing with negligible contribution from analyte profile broadening. These data indicated that the hydrogel coatings imposed 44% reduction in glucose permeability and consequently 26% reduction in the percent recovery. The effect of hydrogel coatings on the time to reach the steady-state recovery was insignificant compared with the time required for convection of glucose in the outlet tubing.

Modeling Leakage Kinetics from Multilamellar Vesicles for Membrane Permeability Determination: Application to Glucose

The glucose permeability of bilayers formed from phosphatidylcholine, Brij30, and sodium octadecyl sulfate has been determined via an enzymatic reaction. Glucose is encapsulated in either uni- or multilamellar vesicles (MLV) and its concentration in the dispersion medium is monitored by spectrophotometry analysis through the rate of glucose oxidase-catalyzed reaction of glucose oxidation. A kinetic model of leakage, taking explicitly into account one, two, or n w-walls ( n w » 1) for the vesicles and assuming an enzymatic Michaelis-Menten behavior, is proposed and used to fit the experimental data. The two-wall model was chosen to fit experimental data obtained on MLV since an average value of 1.7 bilayers was estimated for MLV by cryo-TEM imaging. A permeability value of 5.8 ± 4.4 10 −9 cm/s was found. The proposed model is validated by the measurement of the bilayer permeability deduced from the modeling of glucose leakage from unilamellar vesicles with the same composition. In this latter case, a value of 8.3 ± 0.7 10 −9 cm/s is found for the permeability, which is within the error bar of the value found with MLV.

Glucose biosensor with a hydrophilic polyurethane (HPU) blended with polyvinyl alcohol/vinyl butyral copolymer (PVAB) outer membrane

A high-performance glucose sensor capable of continuous monitoring has been developed. The sensor is based on an enzyme immobilization technique using electropolymerization of a non-conducting poly( p-aminophenol) (pAP) film on a plasma-deposited platinum electrode, followed by the introduction of a hydrophilic polyurethane (HPU) membrane mixed with polyvinyl alcohol/vinyl butyral copolymer (PVAB) as an outer membrane. Use of non-conducting polymer films for immobilization of glucose oxidase (GOx) results in the creation of a uniform film surface well suited for high enzyme loading. The biocompatible HPU membrane blended with optimized amount of amphiphilic PVAB membrane on the enzyme layer displays excellent characteristics that result in extended linear range, prevent sensor fouling and effectively eliminate interferences from sample solutions. The physical properties of mixed outer membranes, such as O 2 and glucose permeability, were also tested. The optimized glucose sensor capable of continuous monitoring was found to have good sensitivity, a wide response range and fast response time (<5 s). The lifetime of the sensor in a buffer solution was over 20 days, while the lifetime in human serum was about 3 days.

Glucose Partition Coefficient and Diffusivity in the Lower Skin Layers

This work aims to estimate the diffusivity and partitioning of glucose in the dermis and the viable epidermis of human skin. The partition coefficient of glucose between phosphate-buffered saline and dermis, tape-stripped epidermis (TSE), stratum corneum (SC), and split-thickness skin, was measured in vitro using human cadaver skin. Glucose permeability across dermis and tape-stripped split-thickness skin (TSS) was measured using side-by-side diffusion cells. Glucose desorption from TSE and human epidermal membrane (HEM) was measured. All measurements were conducted at 32 degrees C. The partition coefficient for glucose [mean +/- SD (no. of samples)] was 0.65 +/- 0.09 (n = 25) for dermis, 0.81 +/- 0.06 (n = 10) for TSE, and 0.53 +/- 0.12 (n = 9) for SC. Glucose diffusivity in dermis was calculated to be 2.64 +/- 0.42 x 10(-6) cm2/s (n = 14). Glucose diffusivities in the viable epidermis estimated from TSS permeation, TSE desorption, and HEM desorption were 0.075 +/- 0.050 x 10(-6) cm2/s (n = 5), 0.037 +/- 0.018 x 10(-6) cm2/s (n = 4), and 1.0 +/- 0.6 x 10(-6) cm2/s (n = 4), respectively. The tissue/buffer partition coefficient of glucose in all skin layers was found to be less than unity, suggestive of excluded volumes in each layer. Glucose diffusivity in human dermis was found to be one third of its value in water, indicative of hindered diffusion related to the structural components of the tissue. A substantially lower value for glucose diffusivity in viable epidermis is suggested.

Dendrimer crosslinked collagen as a corneal tissue engineering scaffold: Mechanical properties and corneal epithelial cell interactions

Generation 2 polypropyleneimine octaamine dendrimers were used to generate highly crosslinked collagen with mechanical properties that would make it appropriate for use as a corneal tissue-engineering scaffold. Crosslinking of a highly concentrated collagen solution (2-4%) was effected using the water-soluble carbodiimide 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC). The multifunctional dendrimers were introduced as novel multifunctional crosslinkers after the activation of the carboxylic acid groups of glutamic and aspartic acid residues in collagen. Glutaraldehyde, a common collagen crosslinker, was used as comparison, as was EDC, itself an alternative crosslinker, which forms "zero-length or self-crosslinking". The mechanical properties resultant gels were determined. Young's modulus of the dendrimer crosslinked gels was significantly higher than that observed with the other crosslinkers, increasing to 5 MPa compared with 0.1 MPa for the EDC crosslinked gels. Transmission electron microscopy (TEM) analysis of the gels demonstrated the presence of fibrils in the thermally gelled collagen controls; no fibrils were observed in the dendrimer crosslinked gels. As a result, the optical transparency of the dendrimer crosslinked collagen was significantly better than that of the collagen thermal gels. The EDC and glutaraldehyde crosslinked gels were generally less transparent than those crosslinked with the dendrimers. Glucose permeation results demonstrated that the dendrimer crosslinked collagen had higher glucose permeability than natural human cornea. Dendrimer crosslinked collagen gels supported human corneal epithelial cell growth and adhesion, with no cell toxicity. In comparison, some potentially cytotoxic effects were observed with glutaraldehyde crosslinked collagen. Overall, the dendrimer crosslinked collagen gels showed promising properties that suggest that these might be suitable scaffolds for corneal tissue engineering and potentially other tissue engineering applications.

Transport in sulfonated poly(phenylene)s: Proton conductivity, permeability, and the state of water

The transport properties of a series of sulfonated poly(phenylene)s were found to strongly correlate to the ion exchange capacity of the polymer. Sulfonated poly(phenylene) membranes have shown promise as proton exchange membranes for fuel cells. In general, these materials have minimal methanol and glucose crossover while maintaining high proton conductivity, which is necessary for efficient operation of fuel cells powered by liquid fuels. Proton conductivity in addition to methanol and glucose permeability were compared to Nafion as a function of ion exchange capacity. It was found that the transport in Nafion membranes was much higher than that in the sulfonated poly(phenylene)s for a given ion exchange capacity. Water content and its absorbed state within membranes were elucidated by differential scanning calorimetry in order to provide insight as to how the transport properties varied between the materials studied. The domain morphology of these ionomers was imaged with transmission electron microscopy in order to contrast the morphological differences between Nafion and the sulfonated poly(phenylene) series.

Kinetics of endothelin‐induced inhibition and glucose permeability of astrocyte gap junctions

Gap junctions contribute to important functions of communicating glial cells in brain physiology and pathology. Endothelins (ETs), a vasoactive family of peptides present in the brain, have been described as potent inhibitors of astrocyte gap junctional communication. Through dye-coupling studies we demonstrate here that this inhibition occurs rapidly and then successively reverses and returns to control levels after 90 min of continuous ET1 or ET3 exposure. In addition, long-term exposure of cells to ET3, which acts mainly on ETB receptors, also desensitized the acute action of ET1, which was previously shown to act through either ETA or ETB receptor sites, or both. The gap junction blocker carbenoxolone did not show any time-dependent desensitization and was fully effective also in cultures treated with ETs for prolonged times. The ETs inhibitory effects were partially prevented when blocking pertussis toxin-sensitive G-proteins, chelating intracellular Ca2+, or omitting extracellular Ca2+. We further show that ETs modulate gap junction-mediated transfer of 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-Y1)amino]-2-deoxyglucose (2-NBDG), a fluorescent glucose molecule, indicating a role of astrocyte gap junction coupling in metabolic trafficking and suggesting the importance of these peptides in the control of intercellular diffusion of energetic compounds. These findings might have particular relevance in early tissue reactions after various cerebral injuries, which commonly involve increased cerebral ET levels.

Preparation and characterization of alginate–carrageenan complex films

AbstractAlginate–carrageenan (Al–Ca) complex films were synthesized and characterized. The Al–Ca ratio and the crosslinking agent type were important factors in determining the pore size of the complex film. The pore size decreased with an increasing carrageenan content and was reduced further by a crosslinking reaction with CaCl2. The most uniform and flexibile film was formed at an Al–Ca ratio of 6:4. The degree of swelling of crosslinked films increased with an increasing carrageenan content. With a combination of CaCl2and ZnSO4, the water content of the film due to swelling was smallest, which was more suitable than with CaCl2alone. The permeabilities of glucose and dextrans for Al–Ca complex films increased as the alginate content increased, because complex films with a high alginate content had large pores. The partition coefficients of glucose and dextrans for films were in a range of 0.2 to 1.0 depending on the contents of alginate and carrageenan. A 6:4 Al–Ca complex film was most stable in a phosphate buffer solution, indicating that the 6:4 content ratio was suitable to maintain the mechanical strength of alginate–carrageenan chains. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3483–3490, 2006