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R D Mitchell

Publications and source records attributed to R D Mitchell.

45 records · Page 3Linked to original sources
PubMed1983

Purification of morphologically intact triad structures from skeletal muscle.

A procedure has been devised for isolation of triads (t-tubule/sarcoplasmic reticulum (SR) junctional complexes) from rabbit skeletal muscle. The procedure consists of preparation of a heavy microsomal fraction followed by two sequential 90-min sucrose gradient centrifugations to enrich the triads. A pyrophosphate/phosphate/magnesium buffer system was introduced to decrease aggregation in order to achieve effective separation. The preparation time is 12 h. Some differences between purified triads isolated by two variants of this method are noted. The purity of the triad fractions has been estimated by particle counting to be in the vicinity of 50%. There is good retention of morphology and Ca++-loading activity and enrichment in Na+,K+-ATPase and adenylate cyclase. The triads are practically devoid of contractile elements, mitochondria, and free plasmalemma, and low in content of light SR. The method for obtaining enriched triads is reproducible, and sufficient yields are obtained for structural, biochemical, and functional characterization.

Adenylyl Cyclases↗
PubMed1983

Morphology of isolated triads.

The triad is the junctional association of transverse tubule with sarcoplasmic reticulum terminal cisternae. A procedure for the isolation of highly enriched triads from skeletal muscle has been described in the previous paper. In the present study, the structural features of isolated triads have been examined by thin-section, negative-staining, and freeze-fracture electron microscopy. In isolated triads, key features of the structure observed in situ have been retained, including the osmiophilic "feet," junctional structures between the transverse tubule and terminal cisternae. New insight into triad structure is obtained by negative staining, which also enables visualization of feet at the junctional face of the terminal cisternae, whereas smaller surface particles, characteristic of calcium pump protein, are not visualized there. Therefore, the junctional face is different from the remainder of the sarcoplasmic reticulum membrane. Junctional feet as viewed by thin section or negative staining have similar periodicity and extend approximately 100 A from the surface of the membrane. Freeze-fracture of isolated triads reveals blocklike structures associated with the membrane of the terminal cisternae at the junctional face, interjunctional connections between the terminal cisternae and t-tubule, and intragap particles. The intragap particles can be observed to be closely associated with the t-tubule. The structure of isolated triads is susceptible to osmotic and salt perturbation, and examples are given regarding differential effects on transverse tubules and terminal cisternae. Conditions that adversely affect morphology must be considered in experimentation with triads as well as in their preparation and handling.

Animals↗
PubMed1983

Preparation of representative samples of subcellular fractions for electron microscopy by filtration with dextran.

A simple method is described for obtaining a representative field of subcellular fractions for thin section electron microscopy. The prefixed sample is admixed together with high molecular weight dextran, filtered onto a Millipore filter, and embedded in polymer. Filtration serves to uniformly distribute structures of different sizes and densities. The dextran serves as a nonosmophilic spacer, increasing the space between individual structures and preventing sample compression during filtration onto Millipore filters. Sample aggregation can also readily be assessed by the procedure.

Dextrans↗
PubMed1979

Cicatricial pemphigoid: a review of eleven cases.

Eleven cases of cicatricial pemphigoid are presented. The clinical, histopathological and immunopathological features of the disease as well as present methods of treatment and dental management are also discussed.

Adolescent↗
PubMedDate not supplied

Oxygen saturation as a screening test for critical congenital heart disease: a preliminary study.

The aim of this study was to assess the utility of arm and leg oxygen saturation as a candidate screening test for the early detection of ductal-dependent left heart obstructive disease. We measured arm and leg oxygen saturation in 2876 newborns admitted to well baby nurseries and 32 newborns with congenital heart disease. Fifty-seven newborns in the well baby nurseries (0.02%) had an abnormal test (leg saturation less than 92% in room air or 7% lower saturation in the leg than in the arm). Four of the 57 had critical congenital heart disease, including 1 with coarctation of the aorta. Of the 32 newborns with congenital heart disease, 11/13 (85%) with left heart obstructive disease had abnormal oxygen saturation tests, as did 15/19 (79%) with other forms of congenital heart disease. Pulse oximetry deserves further study as a screening test for critical congenital heart disease.

Baltimore↗
PubMedDate not supplied

Addition of enemas to oral lavage preparation for colonoscopy is not necessary.

To evaluate whether the addition of enemas to oral electrolyte lavage is helpful for colonoscopic preparation, we conducted a prospective, randomized, observer-blinded trial to compare oral lavage plus enemas with oral lavage alone. The quality of preparation, mucosal visualization, and the volume of retained colonic fluid did not differ between the two groups. Twenty-two percent of the patients in the group who received oral lavage plus enemas compared with 12% of the patients in the group that only received oral lavage stated that they would refuse to repeat the preparation for future colonoscopic examination. Seventeen percent of the patients in the group that received oral lavage plus enemas demonstrated anorectal trauma or inflammation compared with only 5% in the group that received oral lavage alone (p = 0.09). These results indicate that the addition of enemas to oral lavage preparation for colonoscopic evaluation cannot be routinely recommended. However, enemas may be considered on an individual basis in the occasional patient unable to consume the complete oral lavage or in whom residual stool is found during colonoscopic evaluation after oral lavage preparation.

Colonoscopy↗
PubMedDate not supplied

Genotype and sexual influences on growth and muscle development of chicken embryos.

The influence of sex and genotype on growth of chick embryos was studied using eggs from commercial broiler hens mated with broiler strain males (BrBr) or with bantam males (BaBr) and using eggs from bantam females mated to bantam males (BaBa) or to broiler strain males (BrBa). Male BrBr embryos were first significantly heavier than females at 9 days of incubation. The influence of sire's genotype was expressed between 6 and 16 days of incubation but not at 20 days. Dam's genotype, and the associated difference in egg weight, significantly affected embryo weight by 12 days of incubation and by 20 days it alone influenced embryo weight. Plasma insulin-like growth factor-I (IGF-I) levels of BrBr and BaBr embryos did not differ at 8, 10, 12, or 14 days of incubation, nor were there sex differences. There were no genotype differences in whole body protein concentration, DNA concentration or protein:DNA ratios at 4 or 8 days of incubation. At 12 days the pectoralis major DNA concentration of BaBa embryos was significantly higher than that of all other groups. Pectoralis muscle protein concentration of BrBa embryos was significantly lower than those of BaBr embryos at 12 days of incubation, but by 16 days it was highest. The protein:DNA ratios of embryos developing in bantam eggs were significantly lower than those in broiler eggs at 12 days. In summary, genotypic and sex differences in body weight and muscularity that develop after hatching appear to be predetermined by differences in embryonic growth patterns, but there is no clear relationship between embryonic growth, plasma IGF-I concentration or the concentration of DNA or protein in pectoralis muscle.

Age Factors↗