Gamma-tubulin in chicken erythrocytes: changes in localization during cell differentiation and characterization of cytoplasmic complexes.

The mechanism of marginal band (MB) formation in differentiating erythroid cells is not fully understood, and the proteins involved in nucleation of MB microtubules are largely unknown. To gain insights into the function of gamma-tubulin in MB formation, we have followed its distribution in developing chicken erythrocytes and characterized soluble forms of the protein. In early stages of erythroid cells differentiation, gamma-tubulin was present in microtubule-organizing centers, mitotic spindles, as well as on MB. Its subcellular localization changed in the course of differentiation, and in postnatal peripheral erythrocytes gamma-tubulin was found only in soluble forms. After cold-induced depolymerization gamma-tubulin in erythroid cells formed large clusters that were not observed in matured cells, and re-growth experiments demonstrated that gamma-tubulin was not present in distinct nucleation structures at the cell periphery. Soluble gamma-tubulin formed complexes of various size and large complexes were prone to dissociation in the presence of high salt concentration. Interaction of gamma-tubulin with tubulin dimers was revealed by precipitation experiments. gamma-Tubulin occurred in multiple charge variants whose number increased in the course of erythrocyte differentiation and corresponded with decreased binding to MB. The presented data demonstrate for the first time that gamma-tubulin is a substrate for developmentally regulated posttranslational modifications and that the binding properties of gamma-tubulin or its complexes change during differentiation events.     

Potassium transport in Langendorff-perfused mouse hearts assessed by 87Rb NMR spectroscopy.

We studied the fluxes of a potassium congener (Rb(+)) in mouse hearts by (87)Rb MRS at 8.4T. The hearts were loaded with Rb(+) by perfusion with Krebs-Henseleit buffer, in which 50% of K(+) was substituted with Rb(+). We initiated Rb(+) efflux by changing the perfusion medium to Rb(+)-free buffer. Spectra were acquired every 1.85 min, and the kinetics of Rb(+) transport were analyzed by means of monoexponential fits. The rate constants of Rb(+) uptake and efflux were 0.0680 +/- 0.0028 and 0.0510 +/- 0.0051 min(-1), respectively (approximately 30% faster than in the rat heart). The ATP-sensitive potassium channel opener, P-1075 (5 microM), and mitochondrial uncoupler, 2,4-dintrophenol (50 microM), activated Rb(+) efflux from mouse hearts by approximately 35%. The mechanisms responsible for the differences in Rb(+) uptake and efflux under baseline conditions and stimulation, in comparison with rat hearts, are discussed. These data provide a background for studies of cardiac potassium transport in transgenic mouse strains.     

Occurrence of alkaline phosphatase-positive fibers in experimental muscle disorders

The alkaline phosphatase (AP) reaction was carried out on muscle sections from a large series of rats under various experimental neuromuscular disorders. Only denervated and non-innervated muscle fibers stained positively with the AP reaction. In other conditions including degenerating, regenerating, tenotomized and immature muscles the AP reaction was negative. This suggests that the presence of AP-positive fibers in human neuromuscular disorders reflects a concomitant denervation process.     

Computer-aided intrapatient comparison of brain SPECT images: the gray-level normalization issue applied to children with epilepsy.

A tool was developed for automated intrapatient comparison of brain SPECT images, with specific emphasis on gray-level normalization. METHODS: Ictal and interictal (99m)Tc-ethyl cysteinate dimer SPECT images were acquired for 6 children with partial epilepsy (age range, 2-10 y). For each patient, 3-dimensional rigid geometric ictal-to-interictal image registration optimizing different classic criteria (correlation coefficient, ratio uniformity) in a multiscale translation-rotation 6-parameter space was first performed. Gray-level normalization was then performed with different methods, using a 1- or 2-parameter linear model. In the 1-parameter case, the scaling factor was equal to the interictal-to-ictal ratio of the maximum, mean, or median values calculated within different reference volumes (whole brain or cerebellum) or obtained by linear regression between ictal and interictal counts in the brain or by maximizing a robust criterion, the number of deterministic sign changes in the subtraction images. In the 2-parameter case, the scaling factor and additive constant were estimated using these last 2 methods. For each patient, registration validity and normalization plausibility were assessed by considering the correlation scatterplot together with the different normalization lines and by comparing interictal and registered normalized ictal images using a twin display (with isocontours) in the 3 orthogonal planes. Three-dimensional volumes of interest could be selected on coupled interictal-subtraction images for further focused numeric comparison. RESULTS: After a satisfactory and stable geometric registration with both criteria, the different normalization methods led to similar subtraction images for 5 of 6 patients, except the maxima ratio, which gave noticeably different results in 2 patients. For the remaining patient, with highly dissimilar ictal-interictal images, the maxima ratio normalization was obviously wrong and the other 1-parameter methods probably better depicted the data than did the 2-parameter methods. CONCLUSION: When comparing intrapatient brain SPECT images, one should be aware of the potential impact of the gray-level normalization method on clinical interpretation. For ictal-interictal images, simple robust scaling should be recommended. In particular, image maximum should generally not be considered a valid reference, and no additive constant is needed in the linear gray-level normalization model.     

Some international differences in treatment and survival in breast cancer

In a recent study, 5-year survival rates for breast cancer patients in Boston (Massachusetts), Glamorgan (Wales), Slovenia (Yugoslavia) and Tokyo (Japan) were 57.3%, 49.5%, 41.9% and 74.9%, respectively. In this report, data are presented on the types of treatment used in the four areas and on the relationship of differences in treatment practices to the differences in survival rates. Generally, surgically treated patients who also had radiotherapy had lower survival rates than patients in the same area who had similar operations without radiotherapy. In each area, the survival rate was higher for patients who had radical mastectomy than for those who had simple mastectomy. The Japenese patients had the highest survival rate within nearly every treatment and extent-treatment category. Thus, the high survival rate of these patients was not explained by the variables considered. Survival differences between Boston, Glamorgan and Slovenia were largely explained by differences in extent of disease and type of treatment. As the nature of the treatment—survival trends was consistent with the interpretation that treatment tended to be selected according to apparent prognosis, the degree to which treatment customs were determinants of the differences in survival rate among the three areas is uncertain.