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Biomedical subjects

L M Marshall

Publications and source records attributed to L M Marshall.

31 records · Page 2Linked to original sources
PubMed1981

Membrane protein redistribution during differentiation of cultured human erythroleukemic cells.

Human erythroleukemic (K562) cells differentiate along the erythroid differentiation pathway in vitro when 0.05 mM hemin is included in the growth medium. In the presence of the inducer the cells continue to proliferate and, after a delay of 24 to 48 h, start to synthesize hemoglobin. However, during differentiation, no changes in the major cell surface proteins were detected using lactoperoxidase-catalyzed iodination, and no change in the synthesis of spectrin, the major cytoskeletal protein of the mature erythrocyte, was detected by specific immune precipitation. Despite this absence of major changes in cell surface proteins, profound changes take place in the organization of the cell membranes. A process similar but not identical to the enucleation observed in erythroid differentiation in vivo occurs in which a smooth-surfaced cell, about 10 micrometers in diameter, is divided from the nucleus-containing part of the cell. With the exception of ribosomes, these reticulocyte-like cells contain no organelles when examined by transmission electron microscopy, but contain much of the parent cell's hemoglobin, spectrin, and glycophorin.

Actins↗
PubMed1979

The interaction of lectins with the surface of differentiating erythroleukaemic cells.

Friend erythroleukaemic cells can be induced to mature along the erythroid differentiation pathway when an inducing agent such as dimethyl sulphoxide is included in the medium. In the absence of the inducing agent, the 707B line of Friend erythroleukaemic cells is highly agglutinable by the lectins concanavalin A or wheat germ agglutinin. However, 48 h after the induction of differentiation, there is a marked decrease in the agglutination of the cells in the presence of either lectin. This suggests that early in differentiation a change occurs in the cell membrane preceding the onset of globin synthesis which starts approximately 72 h after induction. The change in agglutination by concanavalin A also occurs in the presence of reagents which do not induce haemoglobin synthesis in the 707B line of Friend erythroleukaemic cells but which are able to stimulate the synthesis of this protein in other erythroleukaemic cell lines. The reduction in the agglutinability of the differentiating cells does not seem to result from a reduction in the number of concanavalin A receptors on the cells, nor does it reflect a change in the clustered distribution of concanavalin A receptors in the differentiating cells. Both the control and dimethyl sulphoxide-induced cells show a similar patchy distribution of ferritin-labelled concanavalin A when examined by electron microscopy. Polyacrylamide gel electrophoresis shows little change in the total pattern of protein synthesis by control and differentiating cells when pulse-labelled with [35S] methionine. However, use of 125I-labelled concanavalin A to stain polyacrylamide gels, on which the total proteins of control and differentiating cells had been separated, revealed a profound change in the composition of the concanavalin A-binding proteins. The control, undifferentiated cells contained eleven or more classes of concanavalin A-binding glycoproteins, many of which stained to a lesser degree as the cell density increased. After the onset of differentiation, 2 new concanavalin A-binding glycoproteins appeared within 48 h. One of these proteins has a molecular weight in excess of 180 000 while the other migrated with an apparent molecular weight of approximately 100 000. After erythroid differentiation had progressed for 120 h, these newly synthesized glycoproteins became the major concanavalin A-binding proteins of the erythroleukaemic cells.

Cell Aggregation↗
PubMed1978

Reinnervation of muscle fiber basal lamina after removal of myofibers. Differentiation of regenerating axons at original synaptic sites.

Axons regenerate to reinnervate denervated skeletal muscle fibers precisely at original synaptic sites, and they differentiate into nerve terminals where they contact muscle fibers. The aim of this study was to determine the location of factors that influence the growth and differentiation of the regenerating axons. We damaged and denervated frog muscles, causing myofibers and nerve terminals to degenerate, and then irradiated the animals to prevent regeneration of myofibers. The sheath of basal lamina (BL) that surrounds each myofiber survives these treatments, and original synaptic sites on BL can be recognized by several histological criteria after nerve terminals and muscle cells have been completely removed. Axons regenerate into the region of damage within 2 wk. They contact surviving BL almost exclusively at original synaptic sites; thus, factors that guide the axon's growth are present at synaptic sites and stably maintained outside of the myofiber. Portions of axons that contact the BL acquire active zones and accumulations of synaptic vesicles; thus by morphological criteria they differentiate into nerve terminals even though their postsynaptic targets, the myofibers, are absent. Within the terminals, the synaptic organelles line up opposite periodic specializations in the myofiber's BL, demonstrating that components associated with the BL play a role in organizing the differentiation of the nerve terminal.

Animals↗
PubMed1978

Synaptic transmission to the horizontal cells in the retina of the larval tiger salamander.

1. The receptive field diameter for most horizontal cells far exceeds the lateral spread of processes for any cell. Therefore horizontal cells probably receive synaptic input from neighbours as well as from the photoreceptors. The electrical effects of these two synaptic inputs were studied. 2. We have characterized the electrical properties of the horizontal cell inputs by determining the current-voltage curves in dark and light. These curves were compared with those obtained in the presence of Co2+ or Mg2 was nearly identical to the curve in the light. 4. The putative transmitter substances glutamate, aspartate and GABA depolarized the cells by increasing conductance. Current-voltage curves measured in the presence of these substances intersected the dark and light curves at +50 mV, the same level at which the dark and light curves intersect. 5. The light response of cells uith broad receptive fields, between 1.0 and 2.0 mm, showed little or no change in conductance associated with the light response. The input resistance was near 20 Momega, and the current-voltage curves intersected at an extrapolated potential level near 200 mV. 6. In the presence of ACh, electrical properties of the broad field cells reverted to those of the narrow field cells: the receptive field was reduced to 0.5 mm, the imput resistance increased, and the current-voltage curves intersected near +50 mV. Thus ACh appeared to interrupt synaptic input from neighbouring horizontal cells. 7. The results confirm the suggestion that horizontal cells receive a tonic excitatory input from the photoreceptors which is decreased by light. They show that horizontal cells receive an additional input from their neighbours, not associated with a measurable conductance change. The input from neighbours is selectively interrupted by ACh, but the nature of this synapse and of the cholinergic action is not known.

Acetylcholine↗
PubMed1977

Reinnervation of original synaptic sites on muscle fiber basement membrane after disruption of the muscle cells.

Regenerating axons form new synapses precisely at sites of original synapses in denervated skeletal muscle. To determine what role the muscle cell plays in this phenomenon, we studied reinnervation of frog muscle at intervals after crushing the nerve and damaging the muscle fibers. Damaged muscle fibers degenerate and are phagocytized, but their basement membrane persists and acts as a scaffold for regenerating muscle cells. Specializations of the basement membrane serve to mark original synaptic sites after nerve and muscle have degenerated. Regenerating axons enter the region of damage and form functional synapses with regenerating myofibers. The new nerve terminals are found almost exclusively at the original synaptic sites, demonstrating that the integrity of the original postsynaptic cell is not necessary for topographically precise reinnervation of denervated muscle.

Animals↗
PubMedDate not supplied

Presynaptic control of synaptic channel kinetics in sympathetic neurones.

The kinetic properties of synaptically activated ion channels are an important determinant of the duration of the synaptic currents that produce postsynaptic potentials in autonomic neurones and skeletal muscle. In the two types of principal neurones in frog sympathetic ganglia, B and C cells, a twofold difference in the mean open time of the nicotinic acetylcholine (ACh-gated) ion channels accounts for the twofold difference in the decay rate of their fast excitatory postsynaptic currents (e.p.s.cs). The B and C cells are selectively innervated by two distinct classes of cholinergic preganglionic axons called B and C fibres, respectively. The present study examined the influence of the preganglionic nerve on the expression of synaptic ion channel properties in sympathetic neurones. B cells were denervated surgically and allowed to become innervated solely by preganglionic C fibres. These B cells, innervated by C fibres, acquired slowly decaying e.p.s.cs and long channel open times, characteristics normally seen in C cells only. These findings provide the first evidence that the kinetic properties of postsynaptic channels can be determined by the particular class of axon innervating a neurone.

Action Potentials↗
PubMedDate not supplied

Multiple chemical sensitivity: discriminant validity of case definitions.

In this study, the authors used the University of Toronto's Health Survey self-administered questionnaire to determine discriminant validity of multiple chemical sensitivity definitions. The authors distributed a total of 4,126 questionnaires to adults who attended general, allergy, occupational, and environmental health practices. The authors then matched responses to features selected from existing case definitions posited by Thomson et al.; the National Research Council; Cullen; Ashford and Miller; Randolph; Nethercott et al.; and the 1999 Consensus (references 4-7, 2, 9, and 10, respectively, herein). The overall response rate was 61.7%. The prevalence of reported symptoms was lowest in general practices, was intermediate in occupational health and allergy practices, and was highest in environmental health practices. Features from the definitions presented by Nethercott et al. and the 1999 Consensus (references 9 and 10, respectively, herein) correctly identified more than 80% of environmental health practice patients and more than 70% of general practice patients. Combinations of 4 symptoms (i.e., having a stronger sense of smell than others, feeling dull/groggy, feeling "spacey," and having difficulty concentrating) also discriminated successfully. In summary, features from 2 of 7 case definitions assessed by the University of Toronto Health Survey achieved good discrimination and identified patients with an increased likelihood of multiple chemical sensitivity.

Adolescent↗