Biomedical subjects

W Chu

Publications and source records attributed to W Chu.

129 records · Page 8Linked to original sources

PubMedDate not supplied

Potentiation of acetylcholine-induced responses in freshly isolated rabbit aortic endothelial cells.

Acetylcholine (ACh)-induced membrane hyperpolarization was studied in freshly isolated endothelial cells from rabbit aorta. Ten microM ACh induced transient hyperpolarization due to the opening of Ca(2+)-sensitive K+ channels, sensitive to TEA and charybdotoxin (CTX). The membrane potential response was accompanied by an increase in intracellular Ca2+ [Ca2+]i. Pretreatment of endothelial cells with 20 microM ATP, 0.2 microM bradykinin or 0.1 microM platelet-aggregating factor, which induced either a transient hyperpolarization or no response, changed the subsequent ACh-induced response to a large maintained hyperpolarization. This sustained membrane hyperpolarization was also due to the opening of Ca(2+)-activated K+ channels as confirmed by CTX and TEA blockade, and was related to elevated [Ca2+]i measured by fura-2 fluorescence. Pertussis toxin blocked potentiation, indicating involvement of a G protein. The linkage to receptor-operated Ca2+ (ROC)-entry was suggested by observations that the maintained hyperpolarization during potentiation was dependent on extracellular Ca2+ and was abolished by the ROC blockers SKF-96365 and Ni2+. Inhibition of the Ca2+ pump of the endoplasmic reticulum mimicked the potentiating effect of the agonists. The results suggest that crosstalk between the agonists in endothelial cells involves Ca2+ movements and that this crosstalk is important for the generation of endothelial secretions.

Acetylcholine↗

PubMedDate not supplied

The reaction mechanisms and kinetics of removing azo reactive dye by indirect photolysis approaches.

The photodegradation of azo reactive dye (RR2) in the presence of acetone (ACE) or triethylamine (TEA) via indirect photolysis was investigated. Photolytic experiments were conducted in a merry-go-round photoreactor with 253.7-nm monochromatic UV lamps. The photodegradation of RR2 in aqueous ACE or TEA solution was found to be kinetically controlled by pseudo-first- and zero-order kinetics, respectively. Typically, the photodegradation reaction is more favorable at higher pH. In the presence of TEA, the rate enhancement primarily is a result of the electron transfer from TEA to RR2 and results in the photoreduction of dye chromophore. Photosensitization is likely the dominant mechanism in the presence of ACE. With respect to the decoloration rate, ACE proved to be a promising rate enhancer at elevated concentrations, and the solution color faded rapidly within 5 minutes of retention time. The photodecoloration of RR2 was found to co-occur with photodechlorination and was followed by photodesulfonation at a later stage in which the mineralized end products, including hydrogen, chloride, and sulphorate ions, were detected in approximately stoichiometric amounts.

Acetone↗

PubMedDate not supplied

Modulation of protein release from chitosan-alginate microcapsules using the pH-sensitive polymer hydroxypropyl methylcellulose acetate succinate.

The release characteristics of protein from chitosan-alginate microcapsules prepared using an electrostatic droplet generator were evaluated. The release studies were undertaken in-vitro in simulated gastrointestinal fluids covering the pH range 1.2-8. Chitosan-alginate microcapsules showed unsatisfactory release properties, losing 94% of the encapsulated proteins (bovine serum albumin) over a 24 h period at pH 1.2. Incorporation of a pH-sensitive polymer, hydroxypropyl methylcellulose acetate succinate (HPMCAS), in the microcapsules, by coating the capsule membrane as well as blending with the capsule core polymer in varying ratios, produced significant changes in the release profiles of the microcapsules. At pH 1.2, the modified microcapsules retained up to 60% of the encapsulated protein after 24 h. The results obtained highlight the potential of HPMCAS as a release-modifier in chitosan-alginate microcapsules.

Aerosols↗