Metabolic rate and directional nucleotide substitution in animal mitochondrial DNA

There is marked heterogeneity of nucleotide composition in mitochondrial DNA across divergent animals. Differences in nucleotide composition presumably reflect differences in directional nucleotide substitution for A+T or G+C nucleotides. In mitochondrial DNA, there is A+T directional nucleotide substitution in most (if not all) animals surveyed, and the magnitude of directional A+T nucleotide substitution differs greatly within and among groups. Differences in directional nucleotide substitution among lineages of mammals can be explained by changes in metabolic physiology. This relationship is thought to be mediated by the effect of oxygen radicals because these toxic compounds are by-products of aerobic metabolism and are known mutagens. Association between metabolism and nucleotide composition provides additional evidence in favor of the hypothesis that rates and patterns of nucleotide substitution in mitochondrial DNA can be influenced by factors that impinge on rates of endogenous DNA damage.      

Elemental distribution in striated muscle and the effects of hypertonicity: Electron probe analysis of cryo sections

A method of rapid freezing in supercooled Freon 22 (monochlorodifluoromethane) followed by cryoultramicrotomy is described and shown to yield ultrathin sections in which both the cellular ultrastructure and the distribution of diffusible ions across the cell membrane are preserved and intracellular compartmentalization of diffusabler ions can be quantitated. Quantitative electron probe analysis (Shuman, H., A.V. Somlyo, and A.P. Somlyo. 1976. Ultramicros. 1:317-339.) of freeze-dried ultrathin cryto sections was found to provide a valid measure of the composition of cells and cellular organelles and was used to determine the ionic composition of the in situ terminal cisternae of the sarcoplasmic reticulum (SR), the distribution of CI in skeletal muscle, and the effects of hypertonic solutions on the subcellular composition if striated muscle. There was no evidence of sequestered CI in the terminal cisternae of resting muscles, although calcium (66mmol/kg dry wt +/- 4.6 SE) was detected. The values of [C1](i) determined with small (50-100 nm) diameter probes over cytoplasm excluding organelles over nuclei or terminal cisternae were not significantly different. Mitochondria partially excluded C1, with a cytoplasmic/ mitochondrial Ci ratio of 2.4 +/- 0.88 SD. The elemental concentrations (mmol/kg dry wt +/- SD) of muscle fibers measured with 0.5-9-μm diameter electron probes in normal frog striated muscle were: P, 302 +/- 4.3; S, 189 +/- 2.9;C1, 24 +/- 1.1;K, 404 +/- 4.3, and Mg, 39 +/- 2.1. It is concluded that: (a) in normal muscle the "excess CI" measured with previous bulk chemical analyses and flux studies is not compartmentalized in the SR or in other cellular organelles, and (b) the cytoplasmic C1 in low [K](0) solutions exceeds that predicted by a passive electrochemical distribution. Hypertonic 2.2 X NaCl, 2.5 X sucrose, or 2.2 X Na isethionate produced: (a) swollen vacuoles, frequently paired, adjacent to the Z lines and containing significantly higher than cytoplasmic concentrations of Na and Cl or S (isethionate), but no detectable Ca, and (b) granules of Ca, Mg, and P = approximately (6 Ca + 1 Mg)/6P in the longitudinal SR. It is concluded that hypertonicity produces compartmentalized domains of extracellular solutes within the muscle fibers and translocates Ca into the longitudinal tubules.     

The dependence of reproductive rate on cell size and temperature in freshwater ciliated protozoa

Summary Reproductive rates have been calculated for ten species of ciliated protozoa in defined conditions. Interspecific double log regressions of generation time vs. cell volume have been computed at each of three temperatures (8.5° C, 15° C, and 20° C) indicating a significant dependence of reproductive rate on cell size. Recorded generation times varied from 6.38 h in Vorticella microstoma at 20° C to 1004 h in Spirostomum teres at 8.5° C. These values correspond to a range in r _m (day)^-1 of 2.607 to 0.017 and (day)^-1 of 13.554 to 1.017. The relationship between these data and similar published data for marine ciliates is examined and the value of such regressions in ecological studies of the protozoa is discussed.     

Ultrastructure of Babesia major vermicules from the tick Haemaphysalis punctata as demonstrated by negative staining.

The ultrastructure of Babesia major vermicules was studied in samples derived from the haemolymph of Haemaphysalis punctata adults and negatively stained with phosphotungstic acid. Most of the organelles observed were typical of those found in apicomplexan parasites. These were the apical complex with the polar ring and the ribs, micronemes and subpellicular microtubules. The number of ribs was 27 or 28. The outer membrane of the pellicle was composed of a large number of fibrils running along the length of the parasite. The inner membrane had large numbers of irregularly scattered holes. A cytoplasmic organelle similar to the granular body described in Theileria annulata ookinetes was seen for the first time in a B. major vermicule.     

Linkage of bipolar affective disorders to markers on chromosome 11p is excluded in a second lateral extension of Amish pedigree 110.

Linkage between markers on chromosome 11p and bipolar affective disorders can be excluded in a second large lateral extension of the original Amish Pedigree 110. These results, together with previous negative linkage findings, suggest that there is not one single gene on 11p conferring susceptibility for bipolar affective disorders among the Old Order Amish.     

A P-NMR saturation transfer study of the regulation of creatine kinase in the rat heart

(1) ³¹P nuclear magnetic resonance was used to measure the creatine kinase-catalysed fluxes in Langendorff-perfused rat hearts consuming oxygen at different rates and using either of two exogenous substrates (11 mM glucose or 5 mM acetate). (2) Fluxes in the direction of ATP synthesis were between 3.5–12-times the steady-state rates of ATP utilization (estimated from rates of O₂-consumption), demonstrating that the reaction is sufficiently rapid to maintain the cytosolic reactants near their equilibrium concentrations. (3) Under all conditions studied, the cytosolic free [ADP] was primarily responsible for regulating the creatine kinase fluxes. The enzyme displayed a K_m for cytosolic ADP of 35 μM and an apparent V_max of 5.5 mM/s in the intact tissue. (4) Although the reaction is maintained in an overall steady-state, the measured ratio of the forward flux (ATP synthesis) to the reverse flux (phosphocreatine synthesis) was significantly greater than unity under some conditions. It is proposed that this discrepancy may be a consequence of participation of ATP in reactions other than the PCr /ag ATP or ATP /ag ADP + P_i interconversions specifically considered in the analysis. (5) The results support the view that creatine kinase functions primarily to maintain low cytosolic concentrations of ADP during transient periods in which energy utilization exceeds production.     

Effect of hypoproteinemia on lung fluid balance in awake newborn lambs

To study the influence of plasma protein concentration on fluid balance in the newborn lung, we measured pulmonary arterial and left atrial pressures, lung lymph flow, and concentrations of protein in lymph and plasma of eight lambs, 2-3 wk old, before and after we reduced their plasma protein concentration from 5.8 +/- 0.3 to 3.6 +/- 0.6 g/dl. Each lamb underwent two studies, interrupted by a 3-day period in which we drained protein-rich systemic lymph through a thoracic duct fistula and replaced fluid losses with feedings of a protein-free solution of electrolytes and glucose. Each study consisted of a 2-h control period followed by 4 h of increased lung microvascular pressure produced by inflation of a balloon in the left atrium. Body weight and vascular pressures did not differ significantly during the two studies, but lung lymph flow increased from 2.6 +/- 0.1 ml/h during normoproteinemia to 4.1 +/- 0.1 ml/h during hypoproteinemia. During development of hypoproteinemia, the average difference in protein osmotic pressure between plasma and lymph decreased by 1.6 +/- 2 Torr at normal left atrial pressure and by 4.9 +/- 2.2 Torr at elevated left atrial pressure. When applied to the Starling equation governing microvascular fluid balance, these changes in liquid driving pressure were sufficient to account for the observed increases in lung fluid filtration; reduction of plasma protein concentration did not cause a statistically significant change in calculated filtration coefficient. Protein loss did not influence net protein clearance from the lungs nor did it accentuate the increase in lymph flow associated with left atrial pressure elevation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fluxes of methane and carbon dioxide from a small productive lake to the atmosphere

The fluxes of CH₄ and CO₂ to the atmosphere, and the relative contributions of ebullition and molecular diffusion, were determined for a small hypertrophic freshwater lake (Priest Pot, UK) over the period May to October 1997. The average total flux of CH₄ and CO₂ (estimated from 7 sites on the lake) was approximately 52 mmol m^–2 d^–1 and was apportioned 12 and 40 mmol m^–2 d^–1 toCH₄ and CO₂ respectively. Diffusion across the air-water interface accounted for the loss of 0.4and 40 mmol m^–2 d^–1 of CH₄ and CO₂ respectively whilst the corresponding figures for ebullition losses were 12.0 (CH₄) and 0.23 (CO₂) mmol m^–2 d^–1. Most CH₄ (96%) was lost by ebullition, and most CO₂ (99%) by diffusive processes. The ebullition of gas, measured at weekly intervals along a transect of the lake, showed high spatial and temporal variation. The CH₄ content of the trapped gas varied between 44 and 88% (by volume) and was highest at the deepest points. Pulses of gas ebullition were detected during periods of rapidly falling barometric pressure. Therelevance of the measurements to global estimates ofcarbon emission from freshwaters are discussed.     

The fine structure of Culicinomyces clavisporus invading mosquito larvae

Electron microscope observations were made of the Australian and U.S. strains of Culicinomyces clavisporus infecting mosquito larvae. The wall of the conidium is composed of an inner (primary) layer, an outer (secondary) layer, and an exterior coating of a mucopolysaccharide substance believed responsible for conidial adhesion to the host cuticle prior to germination and penetration. In some instances the wall of the conidium is ruptured during germination and new wall layers and mucoid coating form around the germ tube whereas in other specimens the conidial wall layers extend around the germ tube without fracturing. The most common invasion site is through the larval foregut following ingestion of conidia. The apex of the germ tube presses tightly against the surface of the foregut cuticle and the mucilaginous coating is stripped away. There is evidence to suggest that the host epicuticle, which disappears across the zone of contact with the germ tube, is utilized for nutrition of the invading fungus. A collar of cuticle forms around the germ tube apex and a narrow penetrant hyphae extends into the procuticle. It is believed that cuticular penetration is primarily enzymatic assisted by mechanical pressure. The penetrant hypha swells into an oval cell in the hypodermal region and vegetative hypha then invade the hemocoel. The cells of the hypodermis develop signs of degeneration presumably due to the secretion of toxic substances from the invading hyphae. Host reactions, involving melanization of the host tissues, are sometimes evident among the invading penetrant hyphae in the cuticle or in the hypodermal cells in contact with the fungus. Melanized capsules form around some of the hyphae within the hemocoel. These latter reactions do not directly involve host blood cells and are examples of “humoral encapsulation” similar to that described by other authors during invasion of pathogenic organisms into mosquito larvae and chironomid larvae.     

Do Baseline P-Values Follow a Uniform Distribution in Randomised Trials?

Background

The theory has been put forward that if a null hypothesis is true, P-values should follow a Uniform distribution. This can be used to check the validity of randomisation.

Method

The theory was tested by simulation for two sample t tests for data from a Normal distribution and a Lognormal distribution, for two sample t tests which are not independent, and for chi-squared and Fisher’s exact test using small and using large samples.

Results

For the two sample t test with Normal data the distribution of P-values was very close to the Uniform. When using Lognormal data this was no longer true, and the distribution had a pronounced mode. For correlated tests, even using data from a Normal distribution, the distribution of P-values varied from simulation run to simulation run, but did not look close to Uniform in any realisation. For binary data in a small sample, only a few probabilities were possible and distribution was very uneven. With a sample of two groups of 1,000 observations, there was great unevenness in the histogram and a poor fit to the Uniform.

Conclusions

The notion that P-values for comparisons of groups using baseline data in randomised clinical trials should follow a Uniform distribution if the randomisation is valid has been found to be true only in the context of independent variables which follow a Normal distribution, not for Lognormal data, correlated variables, or binary data using either chi-squared or Fisher’s exact tests. This should not be used as a check for valid randomisation.