Biomedical subjects

D G Simpson

Publications and source records attributed to D G Simpson.

At least 19 recordsLinked to original sources

PubMed1992

Electrophoresis and chromatography of wheat proteins: available methods, and procedures for statistical evaluation of the data.

Analysis of gluten proteins from the wheat grain endosperm has long challenged the analytical chemist. Several hundred unique polypeptides are present, many in large polymers. This complexity, plus useful relationships of composition to genotype and quality, encouraged development and application of electrophoresis and chromatography for gluten analysis. We review the methods of polyacrylamide gel electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, isoelectric focusing and high-performance liquid chromatography available for study of wheat proteins. Singly and in combination, they provide rapid, reproducible, high-resolution separations based on size, charge, or surface hydrophobicity. As challenging and important as the analyses themselves, however, is interpretation of data. Subjective evaluation is sometimes possible, but statistical methods such as similarity scores, clustering, principal components, multiple linear regression, and partial least squares now are increasingly used for data analysis. We review the use of these procedures, and precautions necessary to avoid misinterpretation of data. Optimal evaluation of protein analytical data will enhance the value of such analyses in wheat breeding, marketing, and processing.

Chromatography↗

PubMed1990

Morphological analysis of contracting and quiescent adult rabbit cardiac myocytes in long-term culture.

Isolated rabbit ventricular cardiac myocytes adapt readily to primary culture. As the myocytes spread and flatten over the culture substratum, the myofibrillar apparatus retains a "rod-like" orientation. Development of contractile activity is crucial in the maintenance of the integrity of the myofibrillar apparatus during prolonged culture. Myocytes that fail to beat display morphological indications of atrophy; conversely, myocytes that commence beating show no such morphological signs of myofibrillar disorganization. The subcellular organization of other elements of the contractile apparatus, including the transverse tubular system and the sarcoplasmic reticulum, retain their structural relationship with the myofibrils in beating myocytes but not in quiescent cells. Cultured adult myocytes represent an important model to investigate the influence of mechanical factors on the organization and maintenance of the adult cardiac phenotype.

Animals↗

PubMed1990

Distribution of vinculin in the Z-disk of striated muscle: analysis by laser scanning confocal microscopy.

Vinculin is a major cytoskeletal component in striated muscle, where it has been reported to form a rib-like structure between the cell membrane and the Z-disk termed a costamere. This arrangement of vinculin has been purported to be involved in the alignment of the myofibrils. However, the three-dimensional arrangement of vinculin in relation to the Z-disk of the myofibril was not known. In the present study, we examined the distribution of vinculin in striated muscle with monospecific antibodies using immunofluorescence and laser scanning confocal microscopy. Isolated cardiac and skeletal muscle cells from a variety of species, tissue sections, and neonatal myocytes with developing myofibrils were examined. Optical sectioning in the X-Y and X-Z planes demonstrated that vinculin immunoreactivity was heaviest at the periphery of the cell; however, the immunoreactivity was also distributed within the Z-disk although at a relatively reduced level. This distribution is potentially significant in understanding the physiological significance of vinculin in striated muscle function and in myofibrillogenesis.

Actinin↗

PubMed1990

Steady-state visually evoked potential topography associated with a visual vigilance task.

This paper describes data which demonstrate a correlation between the magnitude of the Steady-State Visually Evoked Potential (SSVEP) and visual vigilance. The SSVEP was recorded from 64 scalp sites and elicited by a 13Hz uniform visual flicker presented continuously while subjects undertook a visual vigilance task. Fifteen right-handed males were required to view three times a series of 180 geometrical shapes comprising a sequence of 60 squares, 60 circles and a further 60 squares. Each viewing of the 180 shapes constituted a trial. Trials 1 and 2 were identical while trial 3 differed from the first two in that one of the circles was modified. Subjects were ignorant as to the location of the modified circle and prior to the third trial, were challenged to identify the modified circle. A comparison of trials 2 and 3 indicated that the appearance of the modified circle was associated with an attenuation of the SSVEP in the occipito/parietal region. The same comparison indicated a pronounced SSVEP attenuation in the centro/parietal region during the interval that subjects were anticipating the appearance of the modified circle. These results suggest a distinction between the cortical activation patterns occurring during different phases of a visual vigilance task.

Adolescent↗

PubMed1989

BUMP: a FORTRAN program for identifying dose-response curves subject to downturns.

BUMP is a FORTRAN implementation of a modified Jonckheere-Terpstra test, proposed by Simpson and Margolin, to test nonparametrically for a dose-response curve when a downturn is possible at high doses. The Jonckheere-Terpstra statistic is commonly used to test for increasing or decreasing trends in dose-response relationships. In many experimental settings, however, a test agent has more than one effect, and a "bump"-shaped dose-response can occur. For instance, increasing the concentration of a certain nutrient on a petri dish may increase the growth rate at low doses yet decrease the growth rate at high doses because of toxicity. The modified test allows one to assess the significance of the initial increase in the dose-response curve and yet to minimize the effect on the conclusions of any downturn at higher doses. A complete system which operates directly on SYSTAT/MYSTAT files is available for the IBM-PC and compatibles; it includes a utility which converts ASCII data files to the SYSTAT/MYSTAT format. The FORTRAN 77 source code is available for those who would like to run BUMP on other machines.

Data Interpretation, Statistical↗

PubMed1986

Assembly and remodelling of myofibrils and intercalated discs in cultured neonatal rat heart cells.

The reorganization of myofibrils and the re-formation of intercalated discs was examined in neonatal rat cardiac muscle cells during the first 72 h of culture. Rhodamine phalloidin was used to monitor the organizational state of the myofibrils and antibodies to desmoplakin and vinculin were used as markers for the presence of desmosomes and fasciae adherentes, respectively. Tiny punctate desmosomes were observed between muscle cells after 24 h and apparently increased in number and/or size between 24 and 48 h in culture. Fasciae adherentes were not detectable with antibodies to vinculin until after 48 h in culture. Well-defined sarcomeres were restored after 48 h in culture. Once formed the sarcomeric organization of the myofibrils was found to be stable provided they were attached to the sarcolemma via intercalated discs. However, if the myofibrils attached to regions of the membrane that lacked intercalated discs the sarcomeres appeared to break down gradually centripetally. When myofibrils attached to the membrane at the free edges of cells that were not in contact with other muscle cells, the striations stopped abruptly at a considerable distance before the myofibril attached to the membrane. These non-striated terminals elongated between 48 and 72 h and were associated with focal contacts that contained vinculin. Overall the results suggest that cell-cell contact may be critical for the stabilization of normal myofibrillar structure in the heart.

Animals↗

PubMed1974