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Biomedical subjects

J Coombs

Publications and source records attributed to J Coombs.

47 records · Page 3Linked to original sources
PubMed1967

Studies on the biochemistry and fine structure of silica shell formation in diatoms. Chemical composition of Navicula pelliculosa during silicon-starvation synchrony.

Changes are reported in total cellular organic carbon, nucleic acids, proteins, carbohydrates, lipids and chlorophylls during the course of silicon-starvation synchrony of Navicula pelliculosa. All constituents increased at the same rate, relative to cell number, for 30 hours of exponential growth during which silicon was depleted from the medium. Increase in cell number then stopped, but net synthesis of most components continued for a further 5 to 7 hours before ceasing. Deoxyribonucleic acids and lipids accumulated throughout the 14 hour silicon-starvation period. When silicon was resupplied, lipid synthesis ceased and organic carbon and carbohydrates decreased slightly. Net synthesis remained low during the 4 hour silicon uptake period but was resumed at higher rates as cell number began to rise. In cultures transferred to the dark 1 hour prior to readdition of silicon, total carbon, carbohydrates, and lipids decreased markedly during silicon uptake and cell separation. This was due in part to conversion of protein which maintained the protein level of the dark cells close to that of cells kept in the light. Mechanisms by which silicon starvation and reintroduction of silicon might affect rates of cellular synthesis are discussed.

Cell Division↗
PubMed1967

Studies on the biochemistry and fine structure of silica shell formation in diatoms. Photosynthesis and respiration in silicon-starvation synchrony of Navicula pelliculosa.

Rates of photosynthesis, measured by oxygen electrode or by (14)CO(2) fixation, dark respiration and (32)P-phosphate incorporation are reported for the silicon-starvation synchrony of the fresh water diatom Navicula pelliculosa. During late exponential growth the rates were consistent with increase in carbon mass. During silicon starvation, rates of carbon dioxide fixation, oxygen evolution and (32)P incorporation fell, and the saturating light intensity decreased from 27,000 lux to 5000 lux. Reintroduction of silicon led to immediate transients in all parameters studied, followed by a prolonged increase in rate of dark respiration and a gradual increase in apparent photosynthesis. During release of daughter cells, the rates of dark respiration decreased as photosynthesis and (32)P incorporation increased. These results are discussed in relation to effects of silicon on the energy metabolism of the diatom.

Carbon Dioxide↗
PubMedDate not supplied

Cyclosporine nephropathy: inhibition of osmoregulatory renal cell transport.

The immunosuppressant agent cyclosporine (Sandimmune) is a calmodulin inhibitor that has potent nephrotoxic properties. Recently, it has been observed that osmoregulation in the proximal tubules of the bony fish Carassius auratus (goldfish) is a calmodulin-regulated cell function. As their mammalian counterparts do, these renal tubule cells swell when exposed to hypotonic solutions. This is followed by a slower volume regulatory decrease phase owing to KCl efflux and osmotically obligated water. The extrusion of potassium and chloride is, in this preparation, a calcium and calmodulin regulated process, respectively. With videometric methods, the effects of both cyclosporine (5, 10, and 50 microM) and Cremophor EL (0.65 mg per ml) on osmoregulation were studied in isolated renal tubules. The tubules were stimulated with hypotonic Ringer's solution in the presence and absence of cyclosporine and Cremophor EL. Cremophor EL did not have toxic effects on cell volume regulation; cyclosporine, however, induced a dose-dependent inhibition of osmoregulation. This is due to a hindrance of ionic efflux rather than a decrease in cellular water permeability. It is concluded that the influence of cyclosporine on cell volume control is due to inhibition of the calmodulin-regulated ionic efflux required for osmoregulation.

Animals↗