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Biomedical subjects

S Quay

Publications and source records attributed to S Quay.

10 recordsLinked to original sources
PubMed1999

Language choice in the earliest utterances: a case study with methodological implications.

In this case study we investigate how early a developing bilingual exposed simultaneously to English and Spanish can make appropriate language choices. We propose two methodological requirements for studies of this kind: (1) detailed records of the development of the child's lexicon; and (2) data collection in more than one language context. Our own study relies on detailed records of the child's cumulative vocabulary from the first word at ten months, and on weekly audiovideo recordings in both English and Spanish contexts from age 1;3. Analysis of the data shows a strong tendency for the language of the child's utterances to match that of the context at ages 1;7-1;8.

Child Language↗
PubMed1995

The bilingual lexicon: implications for studies of language choice.

Lexical gaps in vocabulary development have been acknowledged as a reason for language mixing in young bilingual children. In spite of this, most studies do not take into account whether young bilinguals have the lexical resources to make a choice between their two languages. Inferences are nevertheless still being made about whether or not young bilinguals differentiate between their two languages based on language choice. It is widely believed, however, that young bilinguals do not have the resources to make lexical choices at a pre-syntactic stage of development before age two. A bilingual case study of an infant acquiring Spanish and English from birth to age 1;10 is used to address this issue. Daily diary records and weekly video recordings in the two language contexts are used to construct the child's lexicon and to establish that translation equivalents that make possible language choice are available from the beginning of speech. The results are used to discuss the importance of translation equivalents in the bilingual lexicon for viable interpretations of language choice.

Age Factors↗
PubMed1989

Magnetic resonance imaging of acute myocardial ischemia using a manganese chelate, Mn-DPDP.

Nine adult rats underwent occlusion of the left coronary artery (LCA) to assess the ability of a manganese chelate of N, N'-Bis (pyridoxal-5-phosphate) ethylenediamine-N, N'-diacetic acid (Mn-DPDP), to delineate acute myocardial ischemia. Hemodynamic effects of the contrast medium were tested in the isolated rat heart. Gated transaxial images of the heart at the mid-ventricular level were obtained using a 2 Tesla magnet. A TE of 20 msec and a TR of 1 R-R interval (approximately 250 msec) were used. Images were taken prior to injection of 400 mumol/kg of Mn-DPDP, 2 minutes after injection, and then at 15 minute intervals for one hour. The time between LCA occlusion and injection of contrast averaged 95 minutes. The signal intensity (SI) of normal myocardium was increased by 125 +/- 9% immediately after injection, and did not significantly vary over one hour. SI of ischemic myocardium increased by only 16 +/- 14% immediately after injection, gradually rising to 44 +/- 13% after one hour. Visual discrimination between normal and ischemic myocardium was obtained throughout the study. The percent contrast between normal and ischemic myocardium was 47.2 +/- 6% at 2 minutes after injection, gradually decreasing to a final value of 31.3 +/- 4%. No hemodynamic effects were produced in the isolated heart using concentrations in the perfusate several-fold higher than those expected to be produced by the intravenous injection of 400 mumol/kg Mn-DPDP. Mn-DPDP shows the potential for delineation of the jeopardy area resulting from coronary occlusion for at least one hour after injection of the agent.

Animals↗
PubMed1985

Selective absorption of ultraviolet laser energy by human atherosclerotic plaque treated with tetracycline.

Tetracycline is an antibiotic that absorbs ultraviolet light at 355 nm and preferentially binds to atherosclerotic plaque both in vitro and in vivo. Tetracycline-treated human cadaveric aorta was compared with untreated aorta using several techniques: absorptive spectrophotometry, which demonstrated a distinct absorptive peak at 355 nm in tetracycline-treated plaque that was absent in treated normal vessel; ultraviolet microscopy, which showed that treated atheroma acquired the characteristic fluorescence of tetracycline under ultraviolet light; and tissue uptake of radiolabeled tetracycline, which showed 4-fold greater uptake by atheroma than by normal vessel. In addition, intravenous tetracycline administered to patients undergoing vascular surgery demonstrated characteristic fluorescence in surgically excised diseased arteries. Because of tetracycline's unique properties, we exposed tetracycline-treated and untreated aorta to ultraviolet laser radiation at a wavelength of 355 nm. We found enhanced ablation of tetracycline-treated atheroma compared with untreated atheroma. The plaque ablation caused by ultraviolet laser radiation was twice as extensive in tetracycline-treated vs nontreated plaque (2.2 +/- 0.25 mm vs 1.3 +/- 0.55 mm, p less than 0.017). This study demonstrates the potential of tetracycline plaque enhancement for the selective destruction of atheroma by ultraviolet laser radiation.

Absorption↗
PubMed1981

Voltage-dependent conductance induced by alamethicin-phospholipid conjugates in lipid bilayers.

Alamethicin, a linear 20-amino acid antibiotic, forms voltage-dependent channels in lipid bilayer membranes. We show here that alamethicin-phospholipid conjugates can be prepared by photolysis of unilamellar vesicles containing alamethicin and a phosphatidylcholine analogue with a carbene precursor at the end of the C-2 fatty acyl chain. This result indicates that at least a portion of the alamethicin molecule is in contact with the hydrocarbon moiety of the membrane in the absence of an applied voltage. Furthermore, the alamethicin-phospholipid photoproduct is able to induce a voltage-gated conductance similar to that of natural alamethicin. The importance of these results in terms of mechanisms for channel gating is discussed.

Alamethicin↗
PubMed1977

Effect of pH on the interaction of benzoate and D-amino acid oxidase.

The kinetic and equilibrium dissociation constants of the reversible binding of benzoate to hog kidney D-amino acid oxidase (DAAO) were studied at 19 degrees C over the pH range 5.3-10.5 by means of a stopped-flow apparatus and spectrophotometric titrations. A simple bimolecular reaction of the form second order-first order was observed; a two-step reaction was seen. Analysis of the pH dependence of the bimolecular rate constants and equilibrium dissociation constants is consistent with three ionizable groups which are important for benzoate binding. The pK values of the enzyme-related ionization are 6.3, 9.2, and 9.6. Analysis of the change in extinction coefficient at 360 nm indicates the pK of 9.6 can be assigned to the 3-imino group of the enzyme-bound flavin. The effect of benzoate on the apparent pK for the ionization of the 3-imino group of the enzyme-bound Fad has been reexamined. The presence of benzoate causes an apparent shift of this ionization from a pK value of 9.6 to 10.7.

Animals↗
PubMed1975

Binding proteins and membrane transport.

The recent studies have clearly established two types of active transport systems. One type is membrane-bound and can be observed in membrane vesicles and the other type is osmotic-shock-sensitive and requires binding proteins to produce active transport. It appears that the membrane-bound systems derive cellular energy from the energy-rich membrane state which can be formed from respiration or ATP-hydrolysis, while the binding protein systems are more directly coupled to phosphate bond energy derived from glycolysis or oxidative phosphorylation. The following conclusions concerning the role of the binding proteins are offered: 1. The binding proteins are present in relatively large amounts (approximately 10(-6) or 10%-5) M) and appear to reside in the periplasmic space. 2. They do not appear to be involved in solute translocation steps, although they cantain a second binding site that could interact with membrane components. 3. The binding proteins appear to increase the affinity of the transport system for the solute by interacting with a membrane component. This may substrate for the membrane transport system.

Biological Transport↗