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Biomedical subjects

S Hwang

Publications and source records attributed to S Hwang.

140 records · Page 8Linked to original sources
PubMed1977

Systems approach to vaginal delivery of drugs IV: methodology for determination of membrane surface pH.

A physical model including a diffusional layer in series with the membrane was developed for studying the possible differences between the pH at the membrane surface and that in the bulk solution. Both the membrane-secreted substances (acids and bases) and buffer constituents in the bulk solutions are assumed to contribute to the surface pH. Equations derived for this situation, together with experimental determinations of the acidic dissociation constant of the secreted material, the total secretion flux, the flux of total secreted acidic species, and the diffusion layer thickness, allow estimates to be made of the pH at the membrane surface. With the rabbit vagina, the membrane surface pH was close to that of the bulk solution in most cases. These results were supported by the fact that the absorption of 1-alkanoic acids in pH 2.2 phosphate buffers was relatively constant over the buffer concentration range of 0.003-0.1 M phosphate.

Absorption↗
PubMed1977

Systems approach to vaginal delivery of drugs V: in situ vaginal absorption of 1-alkanoic acids.

The vaginal absorption of a homologous series of ionizable compounds, the 1-alkanoic acids, was studied using a perfusion method with a rib-cage cell surgically implanted in the rabbit vagina. The absorption rates of these compounds followed first-order kinetics. The physical model previously used for the 1-alkanols, but accounting for the pKa and pH effects in the present case was employed in the analysis of the carboxylic acid data. The aqueous diffusion layer thickness was 0.031 cm. The permeability coefficient for the lipoidal pathway increased 3.5-fold per methylene group. Both values agree reasonably well with those obtained in the alcohol study.

Absorption↗
PubMed1976

Kinetics and stoichiometry of light-induced proton release and uptake from purple membrane fragments, Halobacterium halobium cell envelopes, and phospholipid vesicles containing oriented purple membrane.

We have used flash spectroscopy and pH indicator dyes to measure the kinetics and stoichiometry of light-induced proton release and uptake by purple membrane in aqueous suspension, in cell envelope vesicles and in lipid vesicles. The preferential orientation of bacteriorhodopsin in opposite directions in the envelope and lipid vesicles allows us to show that uptake of protons occurs on the cytoplasmic side of the purple membrane and release on the exterior side. In suspensions of isolated purple membrane, approximately one proton per cycling bacteriorhodopsin molecule appears transiently in the aqueous phase with a half-rise time of 0.8 ms and a half-decay time of 5.4 ms at 21degreesC. In cell envelope preparations which consist of vesicles with a preferential orientation of purple membrane, as in whole cells, and which pump protons out, the acidification of the medium has a half-rise time of less than 1.0 ms, which partially relaxes in approx. 10 ms and fully relaxes after many seconds. Phospholipid vesicles, which contain bacteriorhodopsin preferentially oriented in the opposite direction and pump protons in, show an alkalinization of the medium with a time constant of approximately 10 ms, preceded by a much smaller and faster acidification. The alkalinization relaxes over many seconds. The initial fast acidification in the lipid vesicles and the fast relaxation in the envelope vesicles are accounted for by the misoriented fractions of bacteriorhodopsin. The time constants of the main effects, acidification in the envelopes and alkalinization in the lipid vesicles correlate with the time constants for the release and uptake of protons in the isolated purple membrane, and therefore show that these must occur on the outer and inner surface respectively. The slow relaxation processes in the time range of several seconds must be attributed to the passive back diffusion of protons through the vesicle membrane.

Bacteriorhodopsins↗
PubMed1976

Systems approach to vaginal delivery of drugs II: In situ vaginal absorption of unbranched aliphatic alcohols.

The absorption of unbranched aliphatic alcohols in the rabbit vagina was studied using a perfusion method, and the absorption rates were found to be first order with respect to the drug concentration in the vagina from methanol to octanol. A physical model involving an aqueous diffusion layer in series with a membrane consisting of aqueous pores and lipoidal pathways was used for analyzing the data. The physically based parameters in the model were determined. An effective diffusion layer thickness ("unstirred layer") of around 0.035 cm was found. The increase in the permeability coefficient for the lipoidal pathway per methylene group was around 2.5 for this homologous series.

Absorption↗
PubMed1976

Systems approach to vaginal delivery of drugs III: Simulation studies interfacing steroid release from silicone matrix and vaginal absorption in rabbits.

A composite physical model involving the simultaneous receding boundary release of drug from a drug suspension-silicone polymer matrix system, diffusion across the aqueous layer, and passive transport across the vaginal membrane consisting of parallel lipoidal and aqueous pore pathways is described. Simulation studies with progesterone and hydrocortisone illustrate matrix release-limiting, membrane absorption, and aqueous diffusion layer-limiting cases when the cylindrical silicone delivery device is interfaced with the vaginal membrane of the rabbit.

Cell Membrane↗
PubMed1975

Systems approach to vaginal delivery of drugs I: development of in situ vaginal drug absorption procedure.

In the framework of the development of drug delivery systems for locally administered contraceptive drugs, a reliable method that can afford quantitative evaluation of drug absorption behavior was explored using the rabit doe. A system was constructed based upon perfusing the drug solution in the vaginal tract. For this purpose, a "rib-cage" type cell was constructed and surgically implanted in the rabbit prior to an experiment. The primary purpose of the present paper is to evaluate the method, including the surgical operation and the perfusion system. The absorption experiments were carried out using n-butanol-1minus 14C as the model solute to survey the reproducibility of the absorption behavior. Experiments were conducted with a number of rabbits on several successive days to determine the day-to-day and animal-to-animal variations. The drug disappearance in the reservoir followed first-order kinetics from which the apparent permeability coefficient was calculated. The results indicated that a set of experiments may be carried out on a single animal and that the method generally affords rather high precision.

Absorption↗
PubMedDate not supplied

Characterization of a cDNA encoding the 20-kDa photosystem I light-harvesting polypeptide of Chlamydomonas rinhardtii.

A cDNA encoding the precursor to a major 20-kDa thylakoid polypeptide of Chlamydomonas reinhardtii (P22), previously localized to the photosystem I light-harvesting complex (LHCI), was characterized. N-terminal sequencing of P22 identified the precursor cleavage site. Genomic Southern blots and polymerase chain reaction analyses show that the gene for P22 (Lhca1*1) is single-copy and contains at least one intron. Northern-blot analyses show that Lhca1*1 mRNA is highly regulated in light-dark synchronized cells. The primary sequence and predicted topology of P22 has features characteristic of light-harvesting chlorophyll a/b-binding proteins from higher plants. Sequence comparisons indicate that P22 has significantly greater identity with the Type-I LHCI protein of tomato, compared to other LHC proteins. This result suggests that the divergence of LHCI proteins into the classes found in higher plants may have occurred early in evolution, prior to the separation of green algae and land plants.

Amino Acid Sequence↗
PubMedDate not supplied

Concurrent validity of negative symptom assessments in treatment refractory schizophrenia: relationship between interview-based ratings and inpatient ward observations.

The concurrent validity of interview-based ratings of negative symptoms in 35 inpatients with chronic, treatment refractory schizophrenia was evaluated. Correlations were examined between interview-based ratings of negative symptoms, measured by the Brief Psychiatric Rating Scale and the Positive and Negative Syndrome Scale, and the naturalistic behavior of inpatients as assessed by the Time Sample Behavior Checklist. Higher levels of interview-based negative symptoms were related to reduced interpersonal activity on the inpatient ward, but not to entertainment, instrumental or self-maintenance activities. These findings offer partial support for the concurrent validity of office-based ratings of negative symptoms, and highlight the importance of longitudinal observations of patients for accurate identification of negative symptoms.

Adolescent↗
PubMedDate not supplied

A new strategy for site-specific protein modification: analysis of a Tat peptide-TAR RNA interaction.

Site-specific modification of proteins and peptides with reporter molecules provides a powerful research tool in chemistry and biology. We report the synthesis and application of a tyrosine analogue, N-alpha-Fmoc-3-acetyl-L-tyrosine, for selective modification of proteins. As a model system, we synthesized the human immunodeficiency virus type 1 (HIV-1) Tat peptide (amino acids 47-56) containing the arginine rich RNA-binding region and replaced the Tyr-47 with 3-acetyl-tyrosine. The acetyl-Tyr-Tat peptide was subsequently labeled with a fluorescein derivative to study RNA-protein interactions by fluorescence energy transfer experiments. Our results showed that the Tat peptide binds to the rhodamine labeled TAR RNA with a dissociation constant (KD) of 1.0 +/- 0.5 nM. This strategy of selective protein modification offers a versatile new procedure for labeling peptides of biological interest at a desired site when several nucleophilic side chains of lysine and cysteine are present. These methods would provide tools for postsynthetic peptide modification and introducing biophysical probes for structural and functional analysis of proteins.

Contrast Media↗
PubMedDate not supplied

The housing/health relationship: what do we know?

Research into the relationship between housing and health has frequently been narrowly focused, fragmented, and of marginal practical relevance to either housing or health policy. From an extensive review of the literature, this paper reports on the current state of knowledge about the relationship between housing and health. The research falls into four distinct categories: (1) specific physical or chemical exposures; (2) specific biological exposures; (3) physical characteristics of the house; and (4) social, economic, and cultural characteristics of housing. Much of the general literature on the effects of housing on health cites previous studies and then proceeds to advocate housing policies and strategies that are aimed at improving population health. Studies providing original data on the relationship, which is the vast majority of the literature, focus on very specific physical, chemical, and biological exposures with a known or suspected effect on health within the house, or they focus on the social, economic, and cultural characteristics of the house. The mechanisms through which specific aspects of housing affect health are extremely complicated, but they do exist. Researchers have made a great deal of progress in clarifying some of these mechanisms. A large gap still exists in our knowledge about the links and pathways between housing, socio-economic status and health status.

Environmental Exposure↗