Search PubMed⌕ Search

Biomedical subjects

Y T Lau

Publications and source records attributed to Y T Lau.

52 records · Page 3Linked to original sources
PubMed1992

The oocyte nucleus isolated in oil retains in vivo structure and functions.

We describe a technique for isolating the nucleus of the giant amphibian oocyte under paraffin oil. The method precludes the losses of small solutes and proteins that accompany isolation of nuclei into aqueous media. An individual oocyte is blotted, placed under oil, punctured near the animal pole and then squeezed to gently extrude the nucleus into the oil, thereby avoiding exposure to any aqueous environment. Light and electron microscopy of the oil-isolated nucleus demonstrate that its in vivo morphology is preserved. We also describe techniques that facilitate the study of nuclear functions under oil. Oil-isolated oocyte nuclei retain many in vivo functions for several hours, including size-selective envelope permeability, RNA synthesis and the ability to break down in response to cdc2/cyclin meiotic maturation promoting factor.

Animals↗
PubMed1991

Erythrocyte Li-Na countertransport in hypertension: lack of atrial natriuretic peptide effect.

The rate of erythrocyte Li-Na countertransport and cellular Na+ and K+ contents have been determined in normotensive (NT) and hypertensive (HT, essential hypertension) subjects in the presence and absence of atrial natriuretic peptide (ANP). The rate of Li-Na countertransport was significantly higher in erythrocytes of HT subjects, while the Na+ and K+ contents were not different between the NT and HT groups. We found that ANP (10(-9) and 10(-7) M) had no effect on either the rate of Li-Na countertransport or the cellular Na+ and K+ contents. Since ANP does not influence erythrocyte Na pump and Na-K-Cl cotransport, our results suggest that the Na transport systems of human erythrocytes do not respond to ANP and this lack of response in Li-Na countertransport is independent of the status of hypertension. These findings are consistent with the view that the rate of Li-Na countertransport of erythrocytes may serve as a useful genetic marker for essential hypertension in Chinese. However, the erythrocyte transport systems cannot provide further differentiation utilizing ANP response for essential hypertension.

Adult↗
PubMed1991

Erythrocyte Li transport following different storage conditions.

Erythrocyte Na-Li countertransport has been shown to be elevated in subjects with essential hypertension and has been proposed as a genetic marker. It is also modified by other factors which may exist in the plasma under physiological or pathophysiological conditions. In this investigation, we studied the comparison of storage conditions in plasma and isotonic KCl solution (which has been used as a preservation solution for erythrocyte's Li transport) for cellular Na economy and Na-Li countertransport in erythrocytes from normotensive and hypertensive subjects. We found that plasma-stored cells exhibited higher cellular Na concentration and higher rates of Na-Li countertransport as well as Li leak, than that of KCl solution-stored cells after 20 hr. It is likely that both Na pump and leak permeabilities are changed during plasma storage but the detailed mechanisms involved require further investigation. We also confirmed the usefulness of isotonic KCl solution as a preservation media for erythrocytes in transport studies for up to three days.

Biological Transport↗
PubMed1990

Protein synthesis in rat intestine in vitro: the acute effect of ethanol.

We studied the rate of 3H-leucine incorporation and the acute effect of ethanol on rat jejunum employing a newly-developed method originally for determining rapid solute uptake in vitro. 3H-leucine incorporation was linear up to 12 min and significantly inhibited by 10 microM of cycloheximide, a specific inhibitor for protein synthesis. The inhibition was 86% at 100 microM indicating that the rate of 3H-leucine incorporation was a good index for protein synthetic activity in the intestinal cells. Incorporation was not changed significantly by 8% dilution (with water) but was inhibited by 8% ethanol to less than 1/4 of the control level. Lower concentrations of ethanol had no consistent effects. The action of ethanol was rapid, independent of the precursor level, and was not readily reversible. Although the nature of ethanol's action was not clear, sucrose, in a dose-dependent manner, also significantly inhibited incorporation rapidly, indicated that the action of media hyperosmolality could not be eliminated as part of the cause of inhibition induced by ethanol.

Animals↗
PubMed1989

Nutrient reabsorption of intestine in vitro: effects of ethanol and caffeine.

We studied the effect of ethanol and caffeine on the intestinal reabsorption (jejunum from SD rats) of glucose (Glu) and amino acids. Since most of the studies on the effect of ethanol utilized high concentration, we first characterized the effect of 8% (approximately 1.4 M) ethanol on the activity of Na(+)-coupled nutrient transport. Consistent with previous reports, ethanol (greater than 1 M) was found to inhibit the uptake rates of glucose and its non-metabolizable analogue 3-O-methyl-glucose (3-OMG) by 30%, while leucine (Leu) uptake was inhibited by 60%. Phloridzin, a specific inhibitor for Na(+)-coupled sugar transport, at 1 mM concentration could inhibit Glu and 3-OMG uptake by more than 60% without affecting Leu uptake. We then compared the effects of various concentrations of ethanol on about 20 intestinal segments taken from the same animal. We consistently observed transport inhibition at high concentration of ethanol but at low concentrations (up to 200 mM), there was no consistent effect, while phloridzin or low-Na media (86% of Na replaced by choline) significantly reduced the rate of nutrient uptake in the same experiment. Thus, it appeared that low concentrations of ethanol had no significant effect on Na(+)-coupled nutrient uptake. We also determined the effect of caffeine on intestinal 3-OMG uptake. At concentration of 0.05 mM, caffeine inhibited 3-OMG uptake by about 15% (p less than 0.05). The level of inhibition was not significantly different at 0.5 mM, but a slightly higher level of inhibition (20%) was reached at 5 mM. The action of caffeine could be mimicked by dibutyryl cAMP (1 mM).

3-O-Methylglucose↗
PubMed1988

Potassium salt microinjection into Xenopus oocytes mimics gonadotropin treatment.

Gonadotropin stimulates protein synthesis and growth in ovarian oocytes. The hormone is also known to modify transfollicular K+ fluxes and is now shown to cause increased intraoocytic K+ activity (aK). The hormone's effect on aK was duplicated by microinjecting K+ salts into oocytes which were incubated in paraffin oil. This treatment mimicked the influence of gonadotropin on both the rate of protein synthesis and the synthesis of specific polypeptides. These findings suggest that gonadotropin-stimulated oocyte growth is attributable largely to the hormone's influence on transfollicular K+ fluxes. They support the hypothesis that the K+ flux and aK changes observed during cell activation are critical in causing subsequent increases in protein synthesis and growth.

Animals↗
PubMed1988

A function that relates protein synthetic rates to potassium activity in vivo.

A newly developed experimental system allows the controlled alteration of intracellular K+ activity (aK) and the measurement of amino acid incorporation rates in a single cell, the Xenopus oocyte. We found that as aK is increased by microinjecting a K+ salt, [3H]leucine incorporation (R) varies over a 100-fold range, first stimulated and then inhibited as it passes through four response regions (A-D). In region A (aK approximately 60-100 mM), R is at a nongrowth or maintenance level and is stimulated weakly by increasing aK. In region B (aK approximately 100-130 mM), R is stimulated intensely by increasing aK, roughly tripling with every 10 mM increase. In region C (aK approximately 130-160 mM), R is inhibited intensely by increasing aK. Finally, in region D (aK greater than 160 mM), R is inhibited weakly as aK increases. Collectively, the four response regions constitute the oocyte's R/aK response function. The function provides a comprehensive description of how K+ activity influences the rate of protein synthesis in an intact cell. In the subsequent discussion, we compared the oocyte response function with the K+ response determined in cell-free translational systems. While in vivo and in vitro functions are similar, differences exist that may be important in a cellular control system. We then considered the relevance of the oocyte R/aK response function to "normal" processes in the oocyte and in somatic cells, i.e., those in which aK is varied by physiological changes in the plasma membrane. We concluded that the intensely stimulatory region B is importantly involved in hormonal action and other growth-activating processes and that the entire R/aK response function may play a role in control of protein synthesis during the cell cycle.

Animals↗
PubMed1988

Penicillium marneffei infection: an underdiagnosed disease?

Penicillium marneffei is a rare human pathogen that often causes problems in clinical and histological diagnosis. A patient who presented with autoimmune haemolytic anaemia and hepatosplenomegaly, and was subsequently found to be suffering from disseminated Penicillium marneffei infection, is reported. The liver biopsy showed epithelioid cell granulomas only, and tuberculosis was initially considered the most likely diagnosis. The correct diagnosis became evident in a subsequent colonic biopsy, which showed extensive infiltration by penicillium-laden macrophages.

Bacterial Infections↗
PubMed1984

Water, potassium, and sodium during amphibian oocyte development.

Water, K+, and Na+ were measured in Rana pipiens oocytes during growth and prematurational development using low-temperature microdissection. Whole oocytes were analyzed during previtellogenic and vitellogenic growth. Ooplasm and germinal vesicle (nucleus) were analyzed at the onset and conclusion of vitellogenic growth. In previtellogenic oocytes (less than 40 micrograms), water, K+, and Na+ concentrations resembled those in somatic cells and were independent of cell size. With the onset of yolk deposition, water and K+ concentrations progressively decreased and Na+ progressively increased. These changes were restricted to ooplasm, the site of yolk deposition. In full-grown oocytes, vegetal ooplasm, with greater yolk density than animal ooplasm, contained less water and K+ and more Na+ than animal ooplasm. Collectively, the data indicate that yolk is poorer in water and K+ and richer in Na+ than yolk-free ooplasm (cytoplasm) or nucleoplasm. Yolk concentrations were estimated to be approximately 32%, water, approximately 69 meq K+/liter H2O, and approximately 94 meq Na+/liter H2O. Several nonyolk parameters, such as cation activities and nucleoplasmic binding, also appear to change during oogenesis.

Animals↗
PubMed1984

Regional water changes during oocyte meiotic maturation: evidence of ooplasmic segregation.

Cryomicrodissection was used to measure the intraoocytic distribution of water before and during meiotic maturation in Rana pipiens oocytes. Animal ooplasm contained about 10% more water in matured than in ovarian oocytes. The increase was not dependent on the uptake of extracellular water, occurring even when oocytes were matured in a paraffin oil medium. Rather, animal ooplasm hydration appeared to be due to an increase in the volume fraction occupied by cytoplasm (reduced yolk density) through: (1) migration of cytoplasm from the vegetal to animal hemisphere and (2) mixing of ooplasm with nuclear sap during germinal vesicle breakdown (GVBD). Cytoplasmic migration (or ooplasmic segregation) began prior to GVBD, probably within an hour of exposure to progesterone and appeared to continue through the period of GVBD. The volume of cytoplasm that moved significantly reduced water concentrations in vegetal ooplasm at 6 hr postprogesterone and offset any subsequent water gain due to the mixing of nuclear sap and vegetal ooplasm at GVBD. The findings suggest that segregational movements are among the early maturational changes entrained by progesterone. Ooplasmic segregation is considered in the context of theories of cytomatrix movement in which control resides in regional Ca2+ activity gradients. We address the problem of the vegetal----animal directionality of movement and suggest that the annulate lamellae play a role.

Animals↗
PubMed1984

Artifacts caused by cell microinjection.

The effects of microinjection on Rana pipiens oocytes were determined using cryomicrodissection to measure Na, K, water, and injected radiolabeled sucrose (in gelatin) in the nucleus, animal, and vegetal ooplasm and injected bolus (reference phase, RP). The results point to potential problems in the interpretation of microinjection experiments. When oocytes were injected and incubated in Ringer's solution, nucleus, ooplasm, and RP lost K and sucrose and gained Na. Patterns of loss and gain were complex but were consistent with continuous solute leakage at the injection site causing artifactual intracellular diffusion gradients. In spite of leakage, oocytes completed scheduled meiotic maturation when exposed to progesterone. When oocytes were microinjected and incubated in paraffin oil (a medium in which polar solutes cannot exchange), nuclear and ooplasmic Na, K, and water concentrations remained identical to those in uninjected cells. Neither microinjection per se nor the injected bolus affected intraoocytic solute distributions. These findings imply that, after microinjection in aqueous media, metabolites are lost from and redistribute in cells, and that these artifactual changes are inadequately reflected in the ability of the cell to carry out a complex process. They also show that injection artifacts can be avoided by injecting and incubating cells under paraffin oil.

Animals↗
PubMed1982

Bath osmolality: effect on water permeability of epithelial tissue.

When hyperosmotic gradients from 100 to 500 mosM are used to produce a water flux, the water permeability of live and potassium cyanide (KCN)-poisoned frog skin decreases with increasing osmotic gradients. In addition, as the total bath osmolality (corium + epithelial) increases there is a reduction in tissue water. Examination of the tissue cellular and extracellular compartments shows that cell shrinkage caused by the increasing hyperosmolality of the bathing medium correlates with the decrease in osmotic permeability. When the bath osmolality is held constant and cell volume decreases, there is a decrease in the water permeability. High potassium in the external bathing medium causes cell swelling that is associated with an increase in water permeability. These data support the hypothesis that a number of conditions known to affect the water permeability of frog skin do so partly or wholly as a result of a change in the cell volume, which either directly or indirectly alters the osmotic permeability of a rate limiting barrier, possibly the cell membrane.

Animals↗
PubMed1981

Effects of antidiuretic hormone on kinetic and energetic determinants of active sodium transport in frog skin.

The effects of antidiuretic hormone (ADH) on the rate of transepithelial active Na transport JaNa and the rate of suprabasal O2 consumption of Jsbr were studied in paired hemiskins of frog. Within some 30 min following administration of ADH both JaNa and Jsbr increased to near-maximal levels and then remained stable for at least an hour. On symmetric perturbation of the transepithelial electrical potential delta psi at 6-min intervals, the dependence of JaNa and Jsbr on delta psi was near-linear, both in control and experimental hemi-skins. The stability and near-linearity of the system permitted systematic analysis of the parameters of linear non-equilibrium thermodynamic (NET) and electrical equivalent circuit (EC) formulations. ADH (100 mU/ml) stimulated two of the three NET phenomenological L coefficients, as well as A, the affinity (negative Gibbs free energy) of a metabolic reaction driving transport. Observations at partially depressed levels of transport indicated that the effects of kinetic and energetic factors are to some extent discrete. EC analysis showed stimulation of the amiloride-sensitive conductance Ka, but not of the apparent electromitive force of Na transport 'ENa'. Similar effects were produced by 10 mU/ml of ADH or by 10 mM dibutyryl cyclic AMP, although less marked effects on the L coefficients were noted with the lower concentration of hormone. It is suggested that, in contrast to EC analysis, the NET formulation distinguishes between kinetic and energetic determinants of transport, supporting a dual mechanism of action of ADH.

Animals↗
PubMed1979

Water movement across split frog skin.

A net inward fluid reabsorption (salt-linked flow) has been observed in isolated skin epithelium (split skin) with the same magnitude as in whole skin when identical NaCl Ringer solutions were used to bathe both sides. Split skins also respond to a hyperosmotic sucrose solution bathing the outer (epithelial) surface by generating an outward osmotic flow. A non-linear relationship between osmotic flow and the osmotic gradient has been found in split skin similar to that found in whole skin.

Animals↗
PubMed1979

Evaluation of the rate of basal oxygen consumption in the isolated frog skin and toad bladder.

In the study of active transport it is important to distinguish between oxygen consumption sustaining transepithelial transport and that responsible for other tissue functions (basal metabolism). Since amiloride blocks transepithelial active sodium transport and the associated oxygen consumption in the frog skin and toad bladder, we and others have employed this agent to evaluate the rate of basal metabolism. This technique has recently been criticized in a report that amiloride (and ouabain) increased oxygen consumption when no sodium was available for transport. We have been unable to corroborate these observations. With magnesium-Ringer as external bathing solutions, amiloride and ouabain failed to stimulate oxygen consumption. With sodium-Ringer as external bathing solution amiloride reduced oxygen consumption about 30%, to a level indistinguishable from that found on external substitution of magnesium-Ringer for sodium-Ringer. We conclude that the use of amiloride permits evaluation of the rate of basal metabolism with acceptable accuracy; a possible slight depressant effect of ouabain on basal metabolism remains to be investigated.

Amiloride↗