Catalase depression in malignant liver from chickens with myeloblastosis and Marek's disease.

In rapidly frozen livers from chickens affected with myeloblastosis and Marek's disease and from unaffected control birds there exists a strong correlation between catalase activity and catalase Electron Paramagnetic Resonance (EPR) signal intensities. The diseased chickens had activities and signals reduced to as little as 10% of control values. There were no changes in the EPR parameters in diseased liver and the data support the hypothesis that the lowering in activity is due to lowered catalase levels rather than to catalase inhibition. The rate of transformation of catalase to catalase-formate in liver was studied by freeze-clamping liver in anaesthetised chickens, then warming to 37 degrees for 1 or 2 minutes anaerobiosis, and then refreezing. The only difference of significance in this transformation between diseased and normal livers was the greater percentage of total catalase present as catalase-formate (approximately + 15%) in aerobic diseased liver, which may indicate a lowered production of hydrogen peroxide, relative to formate, in these livers. The rate of transformation was far faster in chickens (t1/2 less than 1 min) than in the rat (t1/2 = 7.7 min).

Electron spin resonance spin label studies of the erythrocyte membrane in Duchenne muscular dystrophy.

The membrane organisation of erythrocytes from patients with Duchenne muscular dystrophy (DMD) and from asymptomatic carriers was studied by the electron spin resonance (ESR) spin label technique. Following the work of Sato et al [1978], we used 2-(14-carboxytetradecyl)-2-ethyl-4, 4-dimethyl-3-oxazolidinyloxyl as probe. We found no significant difference in lipid fluidity at 30 degrees C, measured by the ratio of the line height at central field to that at high field ho/h-1, in DMD patients or carriers compared to appropriate control persons. Our conclusions for the dystrophic boys differ from those of Sato et al [1978], although our data are consistent with theirs within experimental error. We also studied the variation of the ratio ho/h-1 over the temperature range 5-35 degrees C in these individuals. For normal erythrocytes there is a discontinuity in this plot around 15 degrees C that is absent in the erythrocytes of DMD patients [in agreement with the findings of Sato et al, 1978] and also absent in DMD carriers. We suggest the slope of this logarithmic temperature plot over the range 15-35 degrees C is a more useful empirical parameter as the presence of these discontinuities is sometimes uncertain, and using this parameter, we find a clear separation between carriers and controls.

Measurement of erythrocyte membrane elasticity as a diagnostic aid in Duchenne muscular dystrophy.

Using a micropipette aspiration technique, erythrocyte membrane shear elastic modulus was determined for 23 patients with Duchenne muscular dystrophy, for 14 female carriers, and for three control groups (age matched boys and adult males and females). On average the elastic modulus was slightly greater than normal for both affected males and female carriers. However, there was overlap in the values from all groups. The decreased deformability of dystrophic membranes demonstrated by the test is not great enough to be used for carrier detection nor to make the possibility of prenatal diagnosis likely.

Erythrocyte membrane elasticity during in vivo ageing.

Changes in the ability of senescent erythrocytes to pass through the microcirculation may cause them to be trapped in the spleen and removed from the blood. To help understand this process we have measured erythrocyte membrane elasticity, to see whether it changes during in vivo ageing. Human and rabbit red cells were fractionated by isopycnic sedimentation to obtain samples of aged and young cells. These were subjected to micropipette analysis in order to determine their membrane shear elastic modulus. We found that the membrane rigidity did not significantly alter as red cells aged. Previously we have also demonstrated that the changed size and shape of aged cells is unlikely to explain their removal from the circulation (Nash, G.B. and Wyard, S.J. (1981) Biorheology, in the press). Thus we conclude that the lifespan of erythrocytes is not determined by factors related to membrane flexibility or cell shape but may depend on changes in their viscous properties (as suggested by Williams, A.R. and Morris, D.R. (1980), Scand. J. Haematol. 24, 57--62).

Physics.

It is tempting for a lecturer in physics to present medical students with a course which, though sound and vigorous, is more suited to a physicist or engineer. At Guy's Hospital Medical School, physics is taught at a level which the student can follow and the relevance of the subject to the practice of medicine is made clear.

Electron spin resonance spin-label studies of mouse olfactory epithelium.

Three classes of interaction of spin-labeled odors with olfactory membrane of mouse were identified by electron spin resonance spectroscopy and correlated with the olfactory potencies of those odors. Also, variation of fluidity in this membrane was probed using spin-labeled lipids in which the nitroxide group was at increasing distances from the lipid headgroup. A cooperative model of olfactory transduction in agreement with the results is introduced, and typical dose response curves are computed that can predict molecular features necessary for a strong odor.