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Biomedical subjects

J Thompson

Publications and source records attributed to J Thompson.

At least 811 records · Page 45Linked to original sources
PubMed1970

Parallel spindle systems in the small muscles of the rat tail.

1. The examination consisted of a histological analysis using paraffin sections, gold chloride staining and osmic acid techniques.2. The parallel spindle system found in the rat tail muscles is compared with that found in frog muscles. The rat spindle system occasionally included extrafusal fibres.3. It was evident that there are basic Class differences between the frog and rat tail parallel spindles, but it is suggested that they may serve a similar proprioceptive role in muscles having almost isometric contractions.4. Other short muscles of the rat that might have an analogous function to the tail muscles were examined, but only the capitus and deep masseter muscles showed parallel spindle systems, and none contained extrafusal fibres.5. Of other mammals examined, the muscles of the tails of the cat, rabbit, mouse and guinea-pig contained parallel spindles, while the dog and mole showed none in the small sample taken.6. Nerve trunk fibre size histograms, including de-efferented trunks, indicated a high proportion of sensory nerve fibres from the tail (55%), a low motor unit ratio (1:60) and a beta axon motor supply both to the spindles and to the small muscles of the tail.7. A generalized schema of the rat tail anatomy is presented, and a tabulation of the large sensory endings expected to be found in any particular small tail muscle.8. It was concluded that the rat tail has a spindle density enough to provide a proprioceptive sensitivity equivalent to that of a caudal digit.

Animals↗
PubMed1970

Stability and comparative transport capacity of cells, mureinoplasts, and true protoplasts of a gram-negative bacterium.

The outer layers of the cell envelope of a pseudomonad of marine origin were removed by washing the cells in 0.5 m NaCl followed by suspension in 0.5 m sucrose. The term mureinoplast has been suggested for the rod-shaped forms which resulted from this treatment. As previously established, these forms lacked the outer cell wall layers but still retained a rigid peptidoglycan structure. Mureinoplasts remained stable if suspended in a balanced salt solution containing 0.3 m NaCl, 0.05 m MgSO(4), and 0.01 m KCl but, unlike whole cells, lost ultraviolet (UV)-absorbing material if suspended in 0.5 m NaCl or 0.05 m MgCl(2). Sucrose added to the balanced salt solution also enhanced the loss of UV-absorbing material. Addition of lysozyme to suspensions of mureinoplasts in the balanced salt solution produced spherical forms which, by electron microscopy and the analysis of residual cell wall material, appeared to be true protoplasts. Only undamaged mureinoplasts, as judged by their capacity to fully retain alpha-aminoisobutyric acid, were capable of being converted to protoplasts. Protoplasts and undamaged mureinoplasts retained 100% transport capacity when compared to an equal number of whole cells. The Na(+) requirement for transport of alpha-aminoisobutyric acid and the sparing action of Li(+) on this Na(+) requirement were the same for both protoplasts and whole cells. These observations indicate that, in this gram-negative bacterium, the cell wall does not participate in the transport process though it does stabilize the cytoplasmic membrane against changes in porosity produced by unbalanced salt solutions. The results also indicate that the requirements for Na(+) for transport and for the retention of intracellular solutes are manifested at the level of the cytoplasmic membrane.

Aminoisobutyric Acids↗
PubMed1970

K plus-dependent deplasmolysis of a marine pseudomonad plasmolyzed in a hypotonic solution.

When cells of a marine pseudomonad were washed with a solution consisting of 0.3 m NaCl, 0.05 m MgSO(4), and 0.01 m KCl (complete salts), they maintained their normal morphology. When washed with a solution of 0.05 m MgSO(4), they became plasmolyzed as indicated by both phase and electron microscopy. Suspensions of cells washed with 0.05 m MgSO(4) showed an increase in optical density (OD) when 0.3 m NaCl was added, and this was followed by a decrease in OD upon the further addition of 0.01 m KCl. Salts of other monovalent cations were not effective in replacing K(+) in producing the OD decrease. Phase-contrast microscopy revealed that the increase in OD was accompanied by a decrease in cell size, and the decrease in OD, by an increase in the cell size. Both phase and electron microscopy showed that the K(+)-dependent decrease in OD was accompanied by deplasmolysis of the cells. Na(+) was required in the suspending medium in addition to K(+) to obtain deplasmolysis. The intracellular K(+) concentration in cells which had been washed with complete salts and which had retained their normal morphology was found to be 0.290 m. In cells plasmolyzed by washing with 0.05 m MgSO(4), the intracellular K(+) concentration was 0.004 m. Deplasmolyzed cells contained 0.330 m K(+). The membrane profile of plasmolyzed cells was retained when protoplasts were formed. The protoplasts became spherical if incubated in a solution permitting the deplasmolysis of the parent cells. The evidence obtained indicates that plasmolysis and deplasmolysis under the conditions described was due to the loss and gain, respectively, of K(+) by the cells. The effect of Na(+) could be ascribed to its capacity to control the porosity of the cytoplasmic membrane of this organism.

Biological Transport, Active↗
PubMed1969

Cation-activated nucleotidase in cell envelopes of a marine bacterium.

Isolated cell envelopes of a marine bacterium, M.B.3, have been prepared which possess a nonspecific, cation-activated nucleotidase. The cell envelope comprises approximately 35% (dry weight) of the whole cell and contains protein, 60.2%; lipids, 20.7%; hexose, 3.4%; and ribonucleic acid, 4.6%. No deoxyribonucleic acid could be detected in the preparations. The nucleotidase has an essential requirement for Mg(2+); maximum activation at pH 8.0 occurs at a divalent cation concentration of approximately 80 mm. At a Mg(2+) to adenosine 5'-triphosphate (ATP) ratio of 2:1, the enzyme was further stimulated by monovalent cations Na(+), K(+), NH(4) (+), and Li(+). Maximum activity was found at a monovalent ion concentration of approximately 0.3 m. The envelope preparation liberated inorganic orthophosphate (P(i)) from ATP, adenosine 5'-diphosphate (ADP), and adenosine 5'-monophosphate (AMP) at similar rates. Thin-layer and ion-exchange chromatography show that when AMP, ADP, and ATP were utilized as substrate, approximately 1, 2, and 3 moles of P(i), respectively, were produced per mole of adenosine. P(i) was also liberated from the 5'-triphosphates of guanosine, uridine, and cytidine. The enzyme preparation did not attack p-nitrophenyl phosphate, beta-glycerophosphate, or inorganic pyrophosphate. Sulfhydryl inhibitors p-chloromercuribenzoate, N-ethyl maleimide, and iodoacetate had little effect upon the nucleotidase activity. Ca(2+) and ethylenediaminetetraacetic acid caused complete inhibition of the system, whereas ouabain had no effect upon the enzyme activity. The concentrations of Na(+) (0.3 m) and Mg(2+) ions (60 to 80 mm) required for maximum ATP-hydrolyzing activity were similar to those concentrations necessary for maintenance of cell integrity and for the prevention of cell lysis.

Adenine Nucleotides↗