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Biomedical subjects

D S Smith

Publications and source records attributed to D S Smith.

At least 343 records · Page 19Linked to original sources
PubMed1977

Postsynaptic membranes in the electric tissue of Narcine: I. Organization and innervation of electric cells. Fine structure of nicotinic receptor-channel molecules revealed by transmission microscopy.

The ventral, postsynaptic membranes of the electroplaques of Narcine were examined for structures corresponding in location, numbers, position and form with nicotinic acetylcholine receptor-channel molecules. Electron micrographs of conventionally fixed material showed that the thickened outer lamina of these membranes contained about 6100 stained structures/micron 2; and calculations from this packing density and the estimated area of postsynaptic membranes/g tissue yielded a total number of structures within a factor of two of the number of receptor molecules/g determined from the binding of alpha-bungarotoxin. Examination of tissue prepared with a tannic acid/glutaraldehyde fixative revealed that the structures were uniform in character, cylindrical in shape, transmembrane in position, and that each contained a central core. Their diameter matched that of isolated receptor molecules, and their size can account for most of the receptor protein. We conclude that these receptor molecules are largely intramembranous, cylindrical and exhibit transmembrane pores.

Animals↗
PubMed1977

Postsynaptic membranes in the electric tissue of Narcine: IV. Isolation and characterization of the nicotinic receptor protein.

The nicotinic receptor protein of the electric tissue of Narcine was purified in several different media by partial isolation of postsynaptic membranes and affinity chromatography. Protease inhibitors were found to be necessary to prevent degradation of the protein, and both EDTA and Tris buffer were used in addition to prevent intramolecular crosslinking of 44,000 and 58,000 dalton subunits by tissue factors. The intact protein was found to have a molecular weight close to 400,000, and appears to be composed of four subunits of 44,000 daltons, two to three of 48,000, one of 58,000 and one of 65,000. All the subunits are glycoproteins and their amino acid compositions show similar hydrophobicity and acidity, suggesting similar positioning in postsynaptic membranes. Crosslinking experiments showed that acetylcholine and alpha-bungarotoxin bind to the smallest subunit, and suggest the juxtaposition of at least two of these subunits, and of all four toxin molecules bound to a receptor molecule. Morphological studies of the protein in membranes and after purification indicated cylindrial molecules with central cores.

Acetylcholine↗
PubMed1977

Estimation of serum gentamicin by quenching fluoroimmunoassay.

A new type of non-isotopic immunoassay, applied to the determination of serum gentamicin, is reported. The method is based on partial quenching of fluorescence observed when fluorescein-labelled gentamicin is bound by anti-gentamicin serum. The fluorescence intensity of the labelled gentamicin in an unseparated immunoassay incubation mixture therefore serves to indicate the extent of binding, which is related to the amount of competing unlabelled gentamicin present. Precision and accuracy are shown to be similar to those of the best existing methods for gentamicin, while the new assay is more rapid and technically simpler, and avoids the use of expensive radio-chemicals with their attendant health hazard. Assays of patient samples correlate with established bioassay and polarisation fluoroimmunoassay methods.

Evaluation Studies as Topic↗
PubMed1977

Structural cross-bridges between microtubules and mitochondria in central axons of an insect (Periplaneta americana).

The distribution of microtubules and mitochondria in central axons of an insect (Periplaneta americana) is assessed by comparison between counts on micrographs and computed axon random 'models'. These studies show that the observed multiple association of microtubules with individual mitochondria is statistically highly significant. Electron micrographs of thin sections show that linkage is effected by physical cross-bridge, possibly comprising components from the microtubule and mitochondrion. Linear particle arrays are described on the outer mitochondrial membrane in freeze-fracture replicas, and tentatively related to the bridges seen in thin sections. The results are discussed in terms of proposed roles of microtubules in neurons and other cells.

Animals↗
PubMed1976

Polarisation fluoroimmunoassay of gentamicin.

A polarisation fluoroimmunoassay has been developed for the routine determination of gentamicin levels in serum. The method employs fluorescein-labelled gentamicin which is easily, reproducibly and economically prepared and has excellent shelf-life. The assay is fast (minimum incubation time 2 min) and requires 1.25 mul of serum. There is no separation step prior to readout of results. Recovery experiments reveal no serum effects. Intra- and inter-assay coefficients of variation are of the order of 10% or less. Estimations of gentamicin levels in patient serum samples correlate closely with those obtained by bioassay (r = 0.93) and radioimmunoassy (r = 0.97).

Biological Assay↗
PubMed1976

The treatment of connective tissue diseases with antilymphocyte globulin.

Immunosupprissive therapy was carried out using steroids, azathiprine and antilymphocyte globulin in one patient with systemic lupus erythematosus (SLE) and four with dermatomyositis. Response to treatment was based upon clinical evaluation. The patients with SLE and two of the four with dermatomyositis responded favourably to the regime. It is suggested that this preliminary study is sufficiently promising to warrant the creation of a rigidly controlled investigation.

Aged↗
PubMed1975

Structural modulations in the tsetse fly milk gland during a pregnancy cycle.

Gross ultrastructural and histochemical details of the integumental milk glands of the tsetse fly Glossina morsitans have been examined during the pregnancy cycle. Structural evidence for protein secretion is found between Days 3-8 of the nine-day cycle: termination of activity is completed on the day of parturition. Onset of lactation is synchronized with the eclosion of the first instar larva. The changes in cell volume (notably in the extracellular reservoir) occurring throughout the pregnancy cycle are illustrated in electron micrographs, and a one hundred-fold volume increase in the reservoir volume between the inactive phase and the active period is illustrated and discussed in terms of membrane modulation of the limiting membrane of the reservoir. Intracellular membrane changes during the cycle, particularly the development of extensive ER arrays in the actively secreting cell, are illustrated and discussed. It is suggested that cytoplasmic microtubules play a part in maintaining the form of the distended secretory cell, at the height of secretory release and storage. Histochemical observations on the milk secretion, and the contents of the larval gut are presented.

Animals↗
PubMed1975

The distribution of orthogonal assemblies and other intercalated particles in frog sartorius and rabbit sacrospinalis muscle.

Freeze-fracture replicas have been prepared from two fast-acting vertebrate muscles (frog sartorius and rabbit sacrospinalis) and are described with particular reference to the distribution of intercalated particles in the plasma membrane. T-tubule and SR cisternae. Orthogonal assemblies of small particles are present on the A face plasma membrane in each instance, and their distribution (in sartorius) is found to be random with respect to the underlying myofibrillar sarcomere repeat. Such assemblies are not present on A or B faces of T-tubule or SR cisternae. Asymmetric particle distribution is described for fracture faces of the T-tubules and SR: the profuse particle packing of the SR A face is uniform from terminal cisternae to medial fenestrated collar. Intercalated particles are present on A and B faces of T-tubule fractures; more commonly on the latter. These results are compared with studies on insect muscles, and a comparative approach to further studies on the correlation between membrane structure and function is discussed.

Animals↗
PubMed1975

Alveolar type II cells: studies on the mode of release of lamellar bodies.

There is increasing evidence that type II alveolar cells are capable of synthesizing surface active material like that obtained from the airways. However a number of problems remain to be solved before it can be stated conclusively that type II cells synthesize the surface active material of the terminal airspace. Among these problems is that of secretion. A number of previous studies have given evidence of the release of lamellar bodies by merocrine secretion. In this study morphologic evidence is presented which supports the view that secretion of lamellar bodies is accomplished by exocytosis. At the apical surface of type II cells, sites can be found where the limiting membrane of the lamellar body is clearly fused with the type II cell plasma membrane and an open channel exists between the contents of the lamellar body and the alveolar space. At these sites the lamellar contents extrude into the airspace with consequent loss of the highly compact organization of intracellular lamellar bodies. The intactness and continuity of the membranes can be traced for the full extent of the exocytosis site. Freeze-etch replicas of the membranes of type II cells show depressions which may represent the sites of discharged lamellae. In addition, tongue-like folds are seen which could be explained as the extensions of cytoplasm which surround the releasing lamellar body and which may flap over the exocytosis pit after discharge. Micrographs of the alveolar space show disorganized lamellar whorls which appear to be unravelling to produce tubular myelin. In view of the unusually large size and lipid composition of lamellar bodies, a mechanism involving hydration of mucopolysaccharide contents as an aid to expulsion of lamellar contents is suggested.

Animals↗
PubMed1975

Purification of monolayer cell cultures of the endocrine pancreas.

Experimental use of primary cultures of endocrine pancreas is constrained by early, vigorous proliferation of fibroblastoid cells. The addition of heavy metals, sodium ethylmercurithiosalicylate, phenyl mercuric acetate, phenyl mercuric nitrate and sodium aurothiomalate to the culture media selectively destroys these fibroblastoid cells yielding highly enriched, morphologically intact, functionally competent endocrine cells that are capable of cell replication. This action of heavy metals appears to be due to reversible inhibition of sulfhydryl enzymes since glutathione and thioglycolate were demonstrated to completely inhibit the cytotoxic effects of the mercury and gold containing agents, respectively. Certain variables in the application of the mercurial agents to pancreatic endocrine cell cultures were defined, most notably the enhanced sensitivity of fetal vs. neonatal tissue, and in inverse relationship of cell density to effective toxicity. After removal of the heavy metal agent from the culture media, many pancreatic islets send out cytoplasmic projections, containing large numbers of oriented microtubules which serve as bridging units to adjacent endocrine cells. The sustained availability of virtually pure pancreatic endocrine cell cultures, which results from the application of mercury to the culture media will undoubtedly permit many aspects of the cell biology of the endocrine pancreas to be directly and sequentially assailed.

Animals↗
PubMed1975

Fenestrated endothelium of the adrenal gland: freeze-fracture studies.

Little is known of how adrenal hormones pass from the interstitial to the vascular space. We have begun to examine the adrenal endothelium as a barrier to hormone passage, by the freeze-fracturing technique. The endothelium of both cortex and medulla is fenestrated. Fractures from both regions show endothelial cells to be extremely thin in regions where fenestrations are abundant. En face fractures show fenestrae disposed in tracts; the fenestrae reaching a distribution of 35/mu2. In both cortex and medulla there are areas of continuous endothelium which contain caveolae. Structures believed to represent fenestra diaphragms contain randomly disposed particles and occasional pits. We have not identified in replicas the central ring and pore described in thin-sectioned material (Elfvin, 1965). The main differences between freeze-fractured aspects of cortical and medullary endothelium are the greater abundance of caveolae in the medulla and the size of the fenestrae (fenestra rims in the medulla are 525-780 A in diameter; in the cortex 570-1660 A). These differences may reflect the different embryological origins of the medulla and cortex. While caveolae may participate in hormone transport, there is no evidence for this. In the medulla the caveolae are more numerous and may have a function not necessarily related to transport. Possibly, caveolae play a role in processing hormones and related substances. For example, ATP and specific proteins are released as well as epinephrine during exocytosis from chromaffin cells. Epinephrine enters the vascular space but ATP does not. ATPase enzymes are a common feature of caveolae of other endothelia and may occur as well in adrenal endothelium.

Adrenal Cortex↗
PubMed1975

Study of the Gregory blood group in an English family.

An example of anti-Gy-a found during routine antenatal testing is the first recorded example in Europe to be described. Five other Gy(a-) siblings were found in the patient's family from whom blood donations were obtained in the event of a needed transfusion. Although anti-Gy-a was detected in the infant's serum, there was no evidence of haemolytic disease of the newborn, presumably due to the fact that the Gy-a antigen is poorly developed at birth.

Blood Group Antigens↗