Showing papers by "University of Georgia published in 1993"

Interpreting Information Systems in Organizations

Abstract: From the Publisher: A coherent integrated source for an interpretive approach to understanding information systems in organizations to aid readers in their own processes of defining computer systems. Examines four major IS issues--strategy, evaluation, design and development, implementation. Features in-depth case studies to illustrate key points.

Molecular Biology of the LysR Family of Transcriptional Regulators

Abstract: The LysR family is composed of > 50 similar-sized, autoregulatory transcriptional regulators (LTTRs) that apparently evolved from a distant ancestor into subfamilies found in diverse prokaryotic genera. In response to different coinducers, LTTRs activate divergent transcription of linked target genes or unlinked regulons encoding extremely diverse functions. Mutational studies and amino acid sequence similarities of LTTRs identify: (a) a DNA-binding domain employing a helix-turn-helix motif (residues 1-65), (b) domains involved in coinducer recognition and/or response (residues 100-173 and 196-206), (c) a domain required for both DNA binding and coinducer response (residues 227-253). DNA footprinting studies suggest that in the absence of coinducer many LTTRs bind to regulated promoters via a 15-bp dyadic sequence with a common structure and position (near -65). Coinducer causes additional interactions of LTTRs with sequences near the -35 RNA polymerase binding site and/or DNA bending that results in transcription activation.

Recommendations for standards in transthoracic two-dimensional echocardiography in the dog and cat

Abstract: Recommendations are presented for standardized imaging planes and display conventions for two-dimensional echocardiography in the dog and cat. Three transducer locations ("windows") provide access to consistent imaging planes: the right parasternal location, the left caudal (apical) parasternal location, and the left cranial parasternal location. Recommendations for image display orientations are very similar to those for comparable human cardiac images, with the heart base or cranial aspect of the heart displayed to the examiner's right on the video display. From the right parasternal location, standard views include a long-axis four-chamber view and a long-axis left ventricular outflow view, and short-axis views at the levels of the left ventricular apex, papillary muscles, chordae tendineae, mitral valve, aortic valve, and pulmonary arteries. From the left caudal (apical) location, standard views include long-axis two-chamber and four-chamber views. From the left cranial parasternal location, standard views include a long-axis view of the left ventricular outflow tract and ascending aorta (with variations to image the right atrium and tricuspid valve, and the pulmonary valve and pulmonary artery), and a short-axis view of the aortic root encircled by the right heart. These images are presented by means of idealized line drawings. Adoption of these standards should facilitate consistent performance, recording, teaching, and communicating results of studies obtained by two-dimensional echocardiography.

Corporate Image, Recruitment Image And Initial Job Choice Decisions

Abstract: Aspects of corporate image, or the image associated with the name of an organization, and recruitment image--the image associated with its recruitment message--were studied. Data collected from fiv...

Alkaline persulfate oxidation for determining total nitrogen in microbial biomass extracts

Abstract: The CHCl₃ fumigation-extraction method for determining soil microbial N involves the extraction of CHCl₃-fumigated and CHCl₃-unfumigated samples with 0.5 M K₂SO₄, followed by determination of total N in the extracts. Total N is typically determined by Kjeldahl digestion (TKN) with the inclusion of NO⁻₂ and NO⁻₃ present. The determination of total N by TKN has several procedural constraints such as an initial concentration step, long digestion times, and considerable bumping caused by catalyst salts. In contrast, a persulfate oxidation method (TPN) commonly used for determination of total N in sea- and freshwater samples does not require a concentration step and is much simpler and faster than TKN. The objective of this study was to evaluate and adapt the TPN method to measure total N in 0.5 M K₂SO₄ extracts for determination of soil microbial biomass N. Studies were conducted to optimize reagent/sample (R/S) ratio and autoclaving time, and to evaluate the effects of C and N concentrations. These studies showed that complete N recovery can be obtained with a R/S ratio of 1 and an autoclaving time of 30 min in extracts containing as much as 250 mg glucose-C L⁻¹ at a C/N ratio of 10:1. A comparison of the optimized TPN method to TKN for extracts of 12 CHCL₃-fumigated soils indicated that the methods gave the same N recoveries. The use of the TPN method in 0.5 M K₂SO₄ extracts should facilitate more rapid and efficient measurements of soil microbial biomass N.

Forecasting Stock-Return Variance: Toward an Understanding of Stochastic Implied Volatilities

Abstract: We examine the behavior of measured variances from the options market and the underlying stock market. Under the joint hypotheses that markets are informationally efficient and that option prices are explained by a particular asset pricing model, forecasts from time-series models of the stockreturn process should not have predictive content given the market forecast as embodied in option prices. Both in-sample and out-of-sample tests suggest that this hypothesis can be rejected. Using simulations, we show that biases inherent in the procedure we use to imply variances cannot explain this result. Thus, we provide evidence inconsistent with the orthogonality restrictions of option pricing models that assume that variance risk is unpriced. These results also have implicationsfor optimal variance forecast rules.

What Can Molecular and Morphological Markers Tell Us About Plant Hybridization

Abstract: The study of hybrids and their evolutionary significance is often based on a number of tacit assumptions regarding character expression in hybrids. This article examines morphological, chemical, and molecular character expression in hybrids to determine whether traditionally recognized properties of hybrid plants, such as hybrid intermediacy and character coherence, are actually supported by empirical evidence, and also examines the impact of hybrids on phylogenetic analyses. We show that hybrids are a mosaic of both parental and intermediate morphological characters rather than just intermediate ones, and that a large proportion of first (64%) and later generation hybrids (89%) exhibit extreme or novel characters. Chemical character expression in hybrids is more predictable, with predominantly additive or complementary expression for both first generation hybrids (68%) and hybrid taxa (54%). Likewise, the genetic basis, and thus the expression of molecular characters, is well-worked out and pred...

Maximum Likelihood Estimation for a Multifactor Equilibrium Model of the Term Structure of Interest Rates

Abstract: LOUIS SCOTT is associate professor of finance at the University of Georgia in Athens. model of the term structure of interest necessary for the valuation of bonds and interest rate options; and parameter valestimates, are necessary for the implementation of a specific model. This article presents a method for estimating the parameters of a particular class of continuous-time equilibrium models of the term structure. The theoretical framework for the analysis is the model of Cox, Ingersoll, and Ross [1985a, 1985b1, where a general equilibrium model of asset pricing is used to examine the behavior of the term structure and related issues such as the valuation of interest ratecontingent claims. The Cox, Ingersoll, Ross model, hereafter the CIR model, is a single-factor equilibrium model of the term structure that is consistent with an asset pricing equilibrium, free of arbitrage opportunities, and retains the feature that the interest rate must be non-negative. The one-factor model, however, has the undesirable property that all bond returns are perfectly correlated, and it may not be adequate to characterize the term structure of interest rates and its changing shape over time. The advantage of this one-factor model is the relatively simple closed-form solution for bond prices. As CIR show, the model can be extended to a multifactor setting, with closed-form solutions for bond prices. We follow suggestions in CIR and develop a multifactor equilibrium model of the term structure. The primary objective is to estimate the parameters of the processes that drive interest rate changes and determine the number of factors necessary to characterize the term structure adequately over time. This analysis

An unambiguous nomenclature for xyloglucan‐derived oligosaccharides

Abstract: A revised system of abbreviated names is proposed for xyloglucan-derived oligosaccharides. Each (1→4)-linked β-D-glucosyl residue (and the reducing terminal n-glucose moiety) of the backbone is given a one-letter code according to its substituents. The name of the oligosaccharide consists of these code letters listed in sequence from non-reducing to reducing terminus of the backbone

There's more to self-esteem than whether it is high or low: the importance of stability of self-esteem.

Abstract: Study 1 examined the extent to which stability and level of self-esteem predicted cognitive and emotional reactions to interpersonal feedback. Among high self-esteem individuals, instability was associated with acceptance and positive emotions following positive feedback but to rejection and defensiveness following negative feedback. Among low self-esteem individuals, instability was unrelated to reactions to positive feedback but was related to less defensiveness and greater acceptance of negative feedback. Study 2 examined the extent to which variability and importance of specific self-evaluations were associated with instability of global self-esteem. Discussion focused on the roles of level and stability of self-esteem in reactions to evaluations and on the nature of self-esteem instability.

Federal policy for the protection of human subjects: applications to research on social work practice.

Abstract: Federal policy regarding the protection of human subjects in research has led to the creation of institutional review boards (IRBs) at every institution that receives federal funds for research. The function of the IRB is to review research that involves human subjects to ensure that this research is completed in an ethical manner. Social work research undertaken by researchers at federally funded institutions using human subjects and aiming to build knowledge that is generalizable is subject to IRB review, as is any research that is not specifically exempted from IRB oversight by the law. Social work practitioners and researchers who use research designs to evaluate practice effectiveness should comply with the ethical standards of the profession and may be subject to the standards specified in federal policy The relationships among social work research, the IRB, and the evaluation of social work practice are examined in light of the federal policy for protecting human subjects. Guidelines are given as t...

Litter mass loss rates in pine forests of Europe and Eastern United States: some relationships with climate and litter quality

Abstract: The purpose of this study was to relate regional variation in litter mass-loss rates (first year) in pine forests to climate across a large, continental-scale area The variation in mass-loss rate was analyzed using 39 experimental sites spanning climatic regions from the subarctic to subtropical and Mediterranean: the latitudinal gradient ranged from 31 °N to 70 °N and may represent the the largest geographical area that has ever been sampled and observed for the purpose of studying biogeochemical processes Because of unified site design and uniform laboratory procedures, data from all sites were directly comparable and permitted a determination of the relative influence of climateversus substrate quality viewed from the perspective of broad regional scales Simple correlation applied to the entire data set indicated that annual actual evapotranspiration (AET) should be the leading climatic constraint on mass-loss rates (Radj 2 = 0496) The combination of AET, average July temp and average annual temp could explain about 70% of the sites' variability on litter mass-loss In an analysis of 23 Scots pine sites north of the Alps and Carpatians AET alone could account for about 65% of the variation and the addition of a substrate-quality variable was sufficiently significant to be used in a model The influence of litter quality was introduced into a model, using data from 11 sites at which litter of different quality had been incubated These sites are found in Germany, the Netherlands, Sweden and Finland At any one site most ( ≫ 90%) of the variation in mass-loss rates could be explained by one of the litter-quality variables giving concentration of nitrogen, phosphorus or water solubles However, even when these models included nitrogen or phosphorus even small changes in potential evapotranspiration resulted in large changes in early-phase decay rates Further regional subdivision of the data set, resulted in a range of strength in the relationship between loss rate and climatic variables, from very weak in Central Europe to strong for the Scandinavian and Atlantic coast sites (Radj 2 = 0912; AETversus litter mass loss) Much of the variation in observed loss rates could be related to continentalversus marine/Atlantic influences Inland locations had mass-loss rates lower than should be expected on the basis of for example AET alone Attempts to include seasonality variables were not successful It is clear that either unknown errors and biases, or, unknown variables are causing these regional differences in response to climatic variables Nevertheless these results show the powerful influence of climate as a control of the broad-scale geography of mass-loss rates and substrate quality at the stand level Some of these relationships between mass-loss rate and climatic variables are among the highest ever reported, probably because of the care taken to select uniform sites and experimental methods This suggest that superior, base line maps of predicted mass-loss rates could be produced using climatic data These models should be useful to predict the changing equilibrium litter dynamics resulting from climatic change

TEN LIES OF ETHNOGRAPHY: Moral Dilemmas of Field Research

Abstract: As Everett Hughes noted, there is an “underside” to all work. Each job includes ways of doing things that would be inappropriate for those outside the guild to know. Illusions are essential for maintaining occupational reputation, but in the process they create a set of moral dilemmas. So it is with ethnographic work. This article describes the underside of ethnographic work: compromises that one frequently makes with idealized ethical standards. It argues that images of ethnographers—personal and public—are based on partial truths or self-deceptions. The focus is on three clusters of dilemmas: the classical virtues (the kindly ethnographer, the friendly ethnographer, and the honest ethnographer), technical skills (the precise ethnographer, the observant ethnographer, and the unobtrusive ethnographer), and the ethnographic self (the candid ethnographer, the chaste ethnographer, the fair ethnographer, and the literary ethnographer). Changes in ethnographic styles and traditions alter the balance of these d...

A repeating 11-mer amino acid motif and plant desiccation.

Abstract: Among the proteins that accumulate as plant seeds desiccate are several protein families that are composed principally of a tandemly repeated 11-mer amino acid motif Proteins containing the same motif accumulate in the desiccating leaves of a desiccation-tolerant plant species This motif is characterized by apolar residues in positions 1, 2, 5 and 9, and charged or amide residues in positions 3, 6, 7, 8 and 11 An alpha helical arrangement of the 11-mer repeating unit gives an amphiphilic helix whose hydrophobic stripe twists in a right-handed fashion around the helix Should these proteins dimerize via binding of their hydrophobic faces, a right-handed coiled coil would be formed Such a structure has not previously been observed A conceivable function for these proteins in ion sequestration in the desiccated state is proposed

Attention Deficit- Hyperactivity Disorder and Asymmetry of the Caudate Nucleus:

Abstract: The neurologic basis of attention deficit-hyperactivity disorder (ADHD) is poorly understood. Based on previous studies that have implicated metabolic deficiencies in the caudate-striatal region in ADHD, we employed magnetic resonance imaging to investigate patterns of morphology of the head of the caudate nucleus in normal and ADHD children. In normal children, 72.7% evidenced a left-larger-than-right (L > R) pattern of asymmetry, whereas 63.6% of the ADHD children had the reverse (L R) morphologic asymmetry in the region of the caudate nucleus may be related to asymmetries observed in neurotransmitter systems implicated in ADHD. The behavioral symptoms of ADHD may reflect disinhibition from normal levels of dominant hemispheric control, possibly correlated with deviations in asymmetric caudate-striatal morphology and deficiencies in associated neurotransmitter systems.

Does the alternative pathway ameliorate chilling injury in sensitive plant tissues

Abstract: Free radical processes have been observed in senescence and several membrane-associated disorders of plants including chilling, freezing, and desiccation injuries. The mitochondria of plant tissues exposed to low temperatures, and other abiotic and biotic stresses, produce superoxide and/or hydrogen peroxide when electron transport through the cytochrome pathway is impaired due to the energy state of the cell or to stress-induced physical changes in the membrane components. The superoxide and/or hydrogen peroxide produced can diffuse throughout the cell causing peroxidation of membrane lipids which results in membrane disruption, increased permeability and metabolic disturbances, and eventually the visible symptoms of chilling injury. The alternative pathway of electron transport in the mitochondria, which is induced by low temperatures in some plant tissues, can mediate these degradative processes by reducing the level of superoxide generated by the mitochondria.

The influence of seed dispersal mechanisms on the genetic structure of tropical tree populations

Abstract: Seed dispersal mechanisms should have a direct impact on the genetic structure of populations. Species whose seeds are dispersed near the maternal plant (e.g. gravity or wind dispersal) or species whose seeds are deposited in clumps or patches should have more fine-scale genetic structure than species whose seeds are dispersed singly by mobile animals. Furthermore, due to the overlap of seed shadows, species with high adult densities should have less genetic structure than species with lower densities. Allozyme analyses of three tropical tree species belonging to the moist tropical forest of Barro Colorado Island, Republic of Panama, were used to describe variation in the scale and intensity of genetic structure within their populations. The genetic structure of seedlings and immature trees in the low-density, wind-dispersed species (Platypodium elegans) was the coarsest and strongest whereas genetic structure in a population of Swartzia simplex var. ochnacea (high density, bird-dispersed) was both the finest and the weakest. The genetic structure of Alseis blackiana, a high-density, wind-dispersed species was intermediate in both degree and scale. In P. elegans and A. blackiana, which had ‘J’ shaped size distributions, the significant genetic structure seen in the smaller and intermediate diameter classes disappeared in the largest diameter class. The loss of genetic structure was not observed in S. simplex, a species with a more even size distribution.

Survival and growth of Escherichia coli O157:H7 on salad vegetables

Abstract: The influence of modified-atmosphere packaging, storage temperature, and time on survival and growth of Escherichia coli O157:H7 inoculated onto shredded lettuce, sliced cucumber, and shredded carrot was determined. Growth of psychotrophic and mesophilic microorganisms and changes in pH and sensory qualities of vegetables, as judged by subjective evaluation, were also monitored. Packaging under an atmosphere containing 3% oxygen and 97% nitrogen had no apparent effect on populations of E. coli O157:H7, psychotrophs, or mesophiles. Populations of viable E. coli O157:H7 declined on vegetables stored at 5 degrees C and increased on vegetables stored at 12 and 21 degrees C for up to 14 days. The most rapid increases in populations of E. coli O157:H7 occurred on lettuce and cucumbers stored at 21 degrees C. These results suggest that an unknown factor(s) associated with carrots may inhibit the growth of E. coli O157:H7. The reduction in pH of vegetables was correlated with initial increases in populations of E. coli O157:H7 and naturally occurring microfloras. Eventual decreases in E. coli O157:H7 in some samples, e.g., those stored at 21 degrees C, are attributed to the toxic effect of accumulated acids. Changes in visual appearance of vegetables were not influenced substantially by growth of E. coli O157:H7. The ability of E. coli O157:H7 to growth on raw salad vegetables subjected to processing and storage conditions simulating those routinely used in commercial practice has been demonstrated.

Enzymes and proteins from organisms that grow near and above 100 degrees C.

Abstract: Microorganisms that can grow at and above 100 degrees C were discovered a decade ago, and about 20 different genera are now known. These so-called hyperthermophiles are the most ancient of all extant life; all but two genera are classified as Archaea. All have been isolated from geothermal heated environments including deep-sea hydrothermal vents. This group includes some methanogenic and sulfate-reducing species, but the majority are strictly anaerobic heterotrophs that utilize complex peptide mixtures as sources of energy, carbon, and nitrogen. Only a few species are saccharolytic. Most of the hyperthermophiles absolutely depend on the reduction of elemental sulfur (S0) to H2S for significant growth, a property that severely limits their large-scale culture in conventional fermentation systems. Consequently, most physiological and metabolic studies have focused on those that can also grow in the absence of S0, including species of the Archaea, Pyrococcus and Thermococcus, and the bacterium Thermotoga. The fermentative pathways for the metabolism of both peptides and carbohydrates in the Archaea appear to depend upon enzymes that contain tungsten, an element seldom used in biological systems. The mechanisms of S0 reduction and energy conservation remain unclear. Enzymes purified from the S0-reducing hyperthermophiles include proteases, amylolytic-type enzymes, hydrogenases, redox proteins, various ferredoxin-linked oxidoreductases, dehydrogenases, and DNA polymerases, some of which are active up to 140 degrees C. However, complete amino acid sequences are known for only a handful of these proteins, and the three-dimensional structure of only one hyperthermophilic protein has been determined. Potential mechanisms by which proteins and various biological cofactors and organic intermediates are stabilized at extreme temperatures are only now beginning to emerge.

Apoptosis reduces both the in vitro replication and the in vivo infectivity of a baculovirus.

Abstract: Apoptotic programmed cell death occurs when the insect cell line SF-21, derived from Spodoptera frugiperda, is infected with mutants of the baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV) which lack a functional p35 gene. However, infection of the Trichoplusia ni TN-368 cell line with p35 mutants does not result in apoptosis (R. Clem, M. Fechheimer, and L. Miller, Science 254:1388-1390, 1991). We have examined the effect of apoptosis on AcMNPV infections in cell lines and larvae of these two insect species. Production of viral progeny was significantly lower in SF-21 cells infected with p35 mutants than in cells infected with wild-type (wt) or revertant viruses. Viral gene expression was abnormal in SF-21 cells infected with p35 mutants; there was a delay in the transcription and translation of early and late viral genes, a lack of expression of very late genes, and a total cessation of protein synthesis late in the apoptotic process. In vivo analysis revealed that the dose of budded virus required for 50% lethality in S. frugiperda larvae was approximately 1,000-fold higher for p35 mutants than for wt or revertant viruses. In contrast, the replication and infectivity of p35 mutant viruses was equivalent to that of wt AcMNPV during infection of both TN-368 cells and T. ni larvae. Thus, the data indicate that a host apoptotic response provides protection against viral infection at the organismal level and that the p35 gene constitutes a host range determinant for AcMNPV infection.

A gamma-tubulin-related protein associated with the microtubule arrays of higher plants in a cell cycle-dependent manner

Abstract: An antibody specific for a conserved gamma-tubulin peptide identifies a plant polypeptide of 58 kDa. gamma-Tubulin antibody affinity purified from this polypeptide recognizes the centrosome in mammalian cells. Using immunofluorescence microscopy, we determined the distribution of this gamma-tubulin-related polypeptide during the complex changes in microtubule arrays that occur throughout the plant cell cycle. We report a punctate association of gamma-tubulin-related polypeptide with the cortical microtubule array and the preprophase band. As cells enter prophase, gamma-tubulin-related polypeptide accumulates around the nucleus and forms a polar cap from which early spindle microtubules radiate. During metaphase and anaphase, gamma-tubulin-related polypeptide preferentially associates with kinetochore fibers and eventually accumulates at the poles. In telophase, localization occurs over the phragmoplast. gamma-Tubulin-related polypeptide appears to be excluded from the plus ends of microtubules at the metaphase plate and cell plate. Its distribution during the cell cycle may be significant in light of differences in the behavior and organization of plant microtubules. The identification of gamma-tubulin-related polypeptide could help characterize microtubule organizing centers in these organisms.

Linking Real Estate Decisions to Corporate Strategy

Abstract: An organization's real estate decisions will be effective if such decisions support the enterprise's overall business objectives. This result can be achieved only by the explicit consideration of h...

Static critical behavior of three-dimensional classical Heisenberg models: A high-resolution Monte Carlo study.

Abstract: Using both recently developed cluster-algorithm and histogram methods, we have carried out a high-resolution Monte Carlo study of static critical properties of classical ferromagnetic Heisenberg models. Extensive Monte Carlo simulations were performed at several temperatures in the critical region, using an improved cluster-updating scheme, on L\ifmmode\times\else\texttimes\fi{}L\ifmmode\times\else\texttimes\fi{}L simple-cubic and body-centered-cubic systems with L\ensuremath{\le}40. Thermodynamic quantities as a function of temperature in the vicinity of the critical point were obtained by an optimized multiple-histogram method, and the critical temperature and static critical exponents were extracted using finite-size scaling. Our best estimates for the inverse critical temperatures are 0.693 035(37) for the simple-cubic system and 0.486 798(12) for the body-centered-cubic system. Estimated static critical exponents for both systems agree with each other within their respective error bars, and the mean estimates \ensuremath{ u}=0.7048(30) and \ensuremath{\gamma}=1.3873(85) are also in excellent agreement with field-theoretic predictions 0.705(3) and 1.386(4).

Mercury released from dental "silver" fillings provokes an increase in mercury- and antibiotic-resistant bacteria in oral and intestinal floras of primates.

Abstract: In a survey of 640 human subjects, a subgroup of 356 persons without recent exposure to antibiotics demonstrated that those with a high prevalence of Hg resistance in their intestinal floras were significantly more likely to also have resistance to two or more antibiotics. This observation led us to consider the possibility that mercury released from amalgam ("silver") dental restorations might be a selective agent for both mercury- and antibiotic-resistant bacteria in the oral and intestinal floras of primates. Resistances to mercury and to several antibiotics were examined in the oral and intestinal floras of six adult monkeys prior to the installation of amalgam fillings, during the time they were in place, and after replacement of the amalgam fillings with glass ionomer fillings (in four of the monkeys). The monkeys were fed an antibiotic-free diet, and fecal mercury concentrations were monitored. There was a statistically significant increase in the incidence of mercury-resistant bacteria during the 5 weeks following installation of the amalgam fillings and during the 5 weeks immediately following their replacement with glass ionomer fillings. These peaks in incidence of mercury-resistant bacteria correlated with peaks of Hg elimination (as high as 1 mM in the feces) immediately following amalgam placement and immediately after replacement of the amalgam fillings. Representative mercury-resistant isolates of three selected bacterial families (oral streptococci, members of the family Enterobacteriaceae, and enterococci) were also resistant to one or more antibiotics, including ampicillin, tetracycline, streptomycin, kanamycin, and chloramphenicol. While such mercury- and antibiotic-resistant isolates among the staphylococci, the enterococci, and members of the family Enterobacteriaceae have been described, this is the first report of mercury resistance in the oral streptococci. Many of the enterobacterial strains were able to transfer mercury and antibiotic resistances together to laboratory bacterial recipients, suggesting that the loci for these resistances are genetically linked. Our findings indicate that mercury released from amalgam fillings can cause an enrichment of mercury resistance plasmids in the normal bacterial floras of primates. Many of these plasmids also carry antibiotic resistance, implicating the exposure to mercury from dental amalgams in an increased incidence of multiple antibiotic resistance plasmids in the normal floras of nonmedicated subjects.

Mechanical factors in the initiation of eccentric contraction-induced injury in rat soleus muscle.

Abstract: 1. Mechanical factor(s) associated with the initiation of eccentric contraction-induced muscle injury were investigated in isolated rat soleus muscles (n = 180; 42 protocols with 4-6 muscles per protocol). Five eccentric contractions were performed with 4 min between contractions. Three levels of peak eccentric contraction force (100, 125 and 150% of pre-injury maximal isometric tetanic tension, P0), length change (0.1, 0.2 and 0.3 muscle length, L0) and lengthening velocity (0.5, 1.0 and 1.5 L0/s) were utilized. Force was varied with stimulation frequency (10-150 Hz). The eccentric contractions were initiated at muscle lengths of 0.85 or 0.90 L0. Following the fifth eccentric contraction, the muscle was incubated in Krebs-Ringer buffer for 60 min. Peak isometric twitch tension (PT), P0, maximal rate of tension development (+ dP/dt), maximal rate of relaxation (-dP/dt), and creatine kinase (CK) release were measured prior to the five eccentric contractions and at 15 min intervals during the incubation period. Total muscle [Ca2+] was measured after 60 min incubation. 2. The mean (+/- S.E.M.) initial decline in P0 for the muscles performing the most injurious protocol was 13.6 +/- 4.8% (n = 6); P0 in control muscles immediately following performance of five isometric contractions was elevated 1.2 +/- 1.0% (n = 8). These means were different at probability, p = 0.005. Mean [ATP] in muscles immediately following the isometric control and most injurious protocols, respectively, were 16.30 +/- 1.49 and 19.84 +/- 1.38 mumol/g dry wt (p = 0.229). 3. Decrements in P0, PT, +dP/dt, and -dP/dt immediately after the injury protocol were related most closely to the peak forces produced during the eccentric contractions; greater initial declines in P0, +dP/dt and -dP/dt were also observed at higher lengthening velocities independent of peak force. Slow declines in P0 and -dP/dt during the 60 min incubation following the injury protocol were greatest for muscles performing contractions at the longer initial length. CK release was independent of all mechanical factors with the exception of lengthening velocity. CK activity at 45 and 60 min into the incubation period was greater for muscles lengthened at the highest velocity used (1.5 L0/s). Mean total muscle [Ca2+] for muscles performing the eccentric contractions was elevated by 38% over isometric control muscles but the elevation was unrelated to any of the four mechanical factors. 4. These data support the hypothesis that eccentric contraction-induced injury is initiated by mechanical factors, with muscle tension playing the dominant role.(ABSTRACT TRUNCATED AT 400 WORDS)