Biomedical subjects

D G Simpson

Publications and source records attributed to D G Simpson.

35 records · Page 2Linked to original sources

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