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Biomedical subjects

J M Wilkinson

Publications and source records attributed to J M Wilkinson.

At least 145 records · Page 8Linked to original sources
PubMed1976

The identification of two inhibitory cells in each segmental ganglion of the leech and studies on the ionic mechanism of the inhibitory junctional potentials produced by these cells.

The present study identifies a pair of inhibitory cells that are located on each anterolateral margin of a leech segmental ganglion. These cells, which we label as cells 119, are electrically interconnected. These cells give rise to inhibitory junctional potentials (ijp's) in contralteral longitudinal body wall muscle cells. The latencies of the ijp's following spikes in cell 119 are variable. The ijp's are caused by transient increases in premeability to the Cl- ion. Previous studies demonstrated that 5-HT causes a hyperpolarization of body wall muscle cells by increasing the permeability of muscle membrane to the Cl- ion. Accordingly, 5-HT was searched for in the 119 cell bodies, but autoradiography, fine structure, and gas chromatography-mass spectrometry gave no indication that 5-HT was present in these cells. However, the variable latencies of the ijp's may indicate that there is a neuron interposed between cell 119 and the muscle cells. If this is the case, then the interposed neuron should be analyzed for 5-HT. Further experiments to locate the terminals of cells 119 and the cell bodies of the presumed interposed neurons are thus desirable.

Action Potentials↗
PubMed1975

Axonal numbers and sizes in the connectives and peripheral nerves of the leech.

The present study is an electron microscopic analysis of the numbers and sizes of axons in the connectives and nerves of the medicinal leech. In either the right or left connectives for ganglia 14-18, there are approximately 2860 (+/- 294 S.D.) axons. Ninety-seven percent of these axons are less than one micron in diameter. The median connective, Faivre's nerve, contains 97 (+/- 3 S.D.) axons, and 94% of these fibers are smaller than one micron. In the peripheral nerve roots for ganglia 14-18, there are approximately 2351 (+/- 311 S.D.) axons. Ninety-eight percent of the axons in the nerves are less than one micron in diameter. Thus, there are approximately 20,000 axons associated with each of the segmental ganglia 14-18 in the leech, and the vast majority of these fibers are less than one micron in diameter.

Animals↗
PubMed1975

Experience in implementing the Mark III Rad 8 system for radiotherapy dose computations.

Rad 8 is a small, in-house computer system for calculating radiotherapy dose distributions, both for multiple field and rotational external beam techniques and for interstitial and intracavitary redium treatments. Implementing the system has its difficulties, particularly in obtaining the necessary beam profile information. Several approaches have been tried and finally a separate profile generator program was written. Other difficulties encountered with beam data storage were overcome by making minor changes to the system programs. The various calculation techniques have been evaluated, and in general found to be satisfactory, and suitable factors to be used in the inhomogeneity correction for 4 MV X rays have been calculated based on previously published measured data. An option to change beam weightings exists and this can be used to renormalize dose distributions to give percentage isodose curves relative to the prescribed tumour dose. If this procedure is followed dose homogeneity over the target volume can readily be assessed, and the exposure times may easily be calculated from the new weightings. Certain shortcomings in the rotating beam program and the radium program may easily lead to error if extreme care is not exercised.

Computers↗
PubMed1975

The amino acid sequence of troponin I from rabbit skeletal muscle.

The complete amino acid sequence of rabbit skeletal muscle troponin I was determined by the isolation of the cyanogen bromide fragments and the tryptic methionine-containing peptides. Troponin I contains 179 amino acid residues and has a molecular weight of 20864. Its N-terminus is acetylated. Detailed evidence on which the sequence is based has been deposited as Supplementary Publication SUP 50055 (23 pages) at the British Library (Lending Division), Boston Spa, Wetherby, West Yorkshire LS23 7QB, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1975) 145, 5.

Amino Acid Sequence↗
PubMed1972

The regulatory proteins of the myofibril. Separation and biological activity of the components of inhibitory-factor preparations.

1. Inhibitory-factor preparations isolated from myofibrils were shown to consist principally of proteins with molecular weights of 37000 and 23000. Under certain preparative procedures an additional component of molecular weight 14000 was present. 2. The 23000-dalton protein, the inhibitory factor, was the major active component. Its activity was enhanced by tropomyosin. 3. The 14000-dalton component also possessed inhibitory activity, although less than that of the 23000-dalton component when compared on a molar basis. Its activity was not always enhanced by tropomyosin. The 14000-dalton component could not be detected in whole fresh myofibrils and the limited evidence available is compatible with its formation during the preparation of the troponin complex. 4. The 37000-dalton component could not replace the inhibitory factor, calcium-sensitizing factor or tropomyosin as components of the relaxing-protein system. 5. All three components had distinctive amino acid compositions, particularly in their cysteine content.

Actomyosin↗
PubMed1971

Allotypically related sequences in the Fd fragment of rabbit immunoglobulin heavy chains.

The sequence has been completed of the N-terminal 94 residues of the variable section of the Fd fragment of heavy chains from rabbit immunoglobulin G (IgG) of allotype As1. Most of the sequence of the same section from IgG of allotype Aa3 is also reported. These results, in conjunction with a substantial sequence of the variable region of allotype Aa2 reported elsewhere (Fleischman, 1971), show the presence of 16 positions (including six consecutive positions) in which the residue present correlates with the allotype. No allotype-related sequence variation has been found in the constant section of the Fd fragment. This evidence supports the view that two genes code for the heavy chain and it can be used as evidence in favour of somatic mutation as the origin of the variability in the sequence of the N-terminal section. The evolutionary origin of the ;a' locus allotypes of rabbit immunoglobulins remains obscure.

Amino Acid Sequence↗