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Biomedical subjects

J L Costa

Publications and source records attributed to J L Costa.

At least 73 records · Page 4Linked to original sources
PubMed1979

Topography and thickness of air-dried human platelets measured by correlative transmission and scanning electron microscopy.

Human platelets rapidly air-dried on carbon-coated grids were examined by transmission and scanning electron microscopy. Whole cell mounts were photographed in a transmission electron microscope (TEM), coated with gold, and then examined in a scanning electron microscope (SEM). The thickness of the cytoplasm towards the centre of the cells was estimated to be 20-40 nm, and the rim of dense material surrounding the cells was 40 nm thick. Some dense bodies stood out as much as 100 nm above the dried cytoplasm. These measurements are important for evaluating cytoplasmic volume during microprobe analyses of air-dried platelet preparations.

Air↗
PubMed1979

Re-evaluation of the uptake of desoxyfructo-serotonin by human platelets, and of its effect on the uptake of serotonin.

Employing C14-glucose and C14-serotonin (5HT) as precursors, we have synthesized desoxyfructo-5HT [1-desoxy-1-(5-hydroxytryptamine)-D-fructose] labelled either in the sugar or 5HT moieties, and examined the uptake of the labelled substrate by washed human platelets. Desoxyfructo-5HT appears to interact with the 5HT uptake site, effectively inhibiting the uptake of H3-5HT. However, our data indicate that contrary to published reports, the entry of desoxyfructo-5HT into platelet vesicles or cytoplasm is negligible.

Biotransformation↗
PubMed1978

Monoamine oxidase activity in different density gradient fractions of human platelets.

Monoamine oxidase (MAO) activity measured in human platelets is reportedly altered by such drugs as epinephrine, lithium carbonate, and imipramine, and also reduced in a number of clinical disorders. To evaluate whether MAO activity might differ in platelet subpopulations, density gradient centrifugation with arabino-galactan was used to prepare four platelet fractions that differed in weight and volume. MAO activity in the lightest and smallest platelet subpopulation was approximately one-half that in the heaviest and largest subpopulation. Because platelet weight and size are thought to be related to platelet age, it is possible that some drug effects on platelet MAO activity might represent changes in platelet turnover. Factors other than platelet turnover rates may contribute to individual differences in platelet MAO activity, however, since one group of individuals with markedly reduced platelet MAO activity exhibited no shift in the proportion of lighter versus heavier platelets nor in the relative amount of MAO activity in each density gradient subfraction.

Blood Platelets↗
PubMed1978

Fluorinated molecule as a tracer: difluoroserotonin in human platelets mapped by electron energy-loss spectroscopy.

The intracellular distribution of fluorine has been delineated in human platelets incubated with 4,6-difluoroserotonin, utilizing a scanning-transmission electron microscope equipped with an energy-loss spectrometer. Discrete intracellular structures corresponding in location to dense bodies contained high concentrations of fluorine. Electron energy-loss spectroscopy, which apparently can detect less than 10(-20) gram of fluorine in an area of 10 square nonometers, can thus localize fluorinated tracer molecules with biological activity.

Blood Platelets↗
PubMed1978

Comparison of the X537A-induced ionophoric removal of serotonin and tryptamine from intact human platelets.

In the absence of appreciable dense-body release from platelets, X537A causes rapid movement of 90--95% of vesicular H3-5HT into the extracellular medium. X537A can in addition transport to the extracellular medium 20% of the total tryptamine sequestered in platelets. Investigation of the extraction of aqueous 5HT and tryptamine into a chloroform phase, and the subsequent extraction of each of the two amines from a chloroform to an aqueous phase, suggest that 5HT, but not tryptamine, is transported efficiently between aqueous phases through a non-polar solvent. The observed differences in the movement of the two amines through platelet membranes may be attributable to a similar phenomenon.

Anti-Bacterial Agents↗
PubMed1977

In situ observation of dense-body release from hydrated human platelets.

Human-platelet dense bodies (secretory granules) have been visualized by electron microscopy in cells maintained in a hydrated state, and their sequential release after stimulation by thrombin has been observed in situ. The pattern of dense body release from individual platelets suggests that a a portion of the dense body complement of a single cell can be extruded without appreciable change in the position of the remaining dense bodies.

Blood Platelets↗
PubMed1977

Evaluation of the uptake of various amines into storage vesicles of intact human platelets.

1 The uptake of various 3H-labelled amines into a thrombin-releasable compartment of human platelets, thought to represent the platelet vesicular storage pool, has been evaluated. Measurable amounts of 5-hydroxytryptamine (5-HT), dopamine, tyramine, octopamine, and tryptamine accumulate in this pool, and also in a non-thrombin-releasable (cytoplasmic) pool during a 30 min incubation period with 10(-5) M extracellular amine concentrations. 2 No differences in the accumulation of vesicular or cytoplasmic 5-HT, dopamine, and tyramine are found in platelets treated with deprenyl to inhibit platelet monoamine oxidase as compared to controls. 3 Extracellular tyramine or dopamine in concentrations as high as 10(-5) M does not alter the initial rate of 5-HT uptake across the platelet plasma membrane. Similarly, sizable cytoplasmic pools of either amine do not alter the initial rate at which small amounts of 5-HT enter platelet cytoplasm or storage vesicles. 5-HT thus appears to be the preferred substrate for uptake into platelets and for movement from cytoplasm to vesicles.

Biogenic Amines↗
PubMed1977

Quantitative evaluation of the loss of human platelet dense bodies following stimulation by thrombin or A23187.

1. Distributions of dense bodies per platelet were evaluated in unstimulated human platelets and in platelets stimulated to secrete by the addition of varying amounts of thrombin or the ionophore A23187. Since distributions were not Gaussian, they were compared by non-parametric methods. 2. Most distribution obtained following varying levels of dense-body release differed significantly from the control (unstimulated) distribution. In general, distribution from points widely separated in terms of per cent release of total dense-body content also differed significantly. Distributions obtained at points where the total number of dense bodies lost was approximately the same did not differ significantly, regardless of the drug and incubation conditions used to produce the dense-body loss. 3. Dense bodies were lose from platelets during the secretory process (measured as the release of either calcium or ATP), and the number of dense bodies lost correlated at a significant level with the amounts of both substances secreted. 4. Following maximal secretion produced by either thrombin or A23187, a population of dense bodies (refractory dense bodies) remained in platelets. The refractory dense bodies could not have been distributed uniformly among the control populations of either platelets or dense bodies. The distribution of refractory dense bodies could, however, be described by a model in which platelets containing large numbers of dense bodies had a greater proportion of their dense-body complement refractory than did platelets containing fewer dense bodies.

Adenosine Triphosphate↗
PubMed1977

Evaluation of the utility of air-dried whole mounts for quantitative electron microprobe studies of platelet dense bodies.

A variety of electronmicroscope techniques have been used to examine how the air-drying process may affect the dense bodies in whole mounts of platelets. (a) Selected-area-diffraction and electron microprobe studies suggest that the air-drying process can result in the formation of crystalline precipitates of sodium chloride on grid films and platelets. However, no crystals were detected in the calcium-and-phosphorus-containing matrix of dense bodies. (b) Tilting studies show that dense bodies in human platelets are spherical or ellipsoidal in shape. Dense bodies in rabbit platelets, in contrast, appear flattened in a horizontal plane. (c) Human-platelet dense bodies probed with a small (20 nm diameter) spot vary widely in their peak/background ratios for calcium and phosphorus-a finding that suggests that the two elements may not be evenly distributed throughout the dense-body matrix. Nevertheless, when dense bodies are probed with a larger (200 nm diameter) spot, they do not appear to differ appreciably among themselves in their calcium or phosphorus content. The data suggest that with human platelets, air drying may be a preparative procedure which permits comparison by microprobe techniques of dense-body matrix content in platelet populations.

Animals↗
PubMed1977

Subcellular localization of lead in synaptosomes.

The neurotoxicology of lead is reported to involve effects on cholinergic and monoaminergic pathways. However, no information is available on the site of action at which lead exerts neurotoxic effects. The technique of x-ray elemental analysis coupled scanning-transmission mode electron microscopy has been applied to study the in vitro interactions of lead with synaptosomes. To minimize possible translocation effects on elemental distribution, isolated synaptosomes were air dried on EM grids; no fixing or staining procedures were used. In such preparations, synaptosomes and intrasynaptosomal mitochondria were distinguishable. Lead was found only in mitochondria in association with Ca ad P. Thus, lead appears to enter isolated nerve terminals and to be sequestered in mitochondria.

Animals↗