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Biomedical subjects

J Koenig

Publications and source records attributed to J Koenig.

At least 37 records · Page 2Linked to original sources
PubMed1995

Functional and structural recovery of myotubes from mice with muscular dysgenesis after co-culture with normal, non-myoblastic cells.

Muscular dysgenesis is a mutation which is characterized by paralysis of skeletal muscle cells. Excitation-contraction coupling is deficient and muscle cells display atypical ultrastructure. In vitro, mutant myotubes recover a normal phenotype when co-cultured with spinal cord cells from normal animals or with normal fibroblasts. We have shown that other types of cells, eg certain glial cells present in the spinal cord or in other tissues, have this capacity. In contrast, intervention of neurons in the recovery does not appear likely. Very different types of non-myoblastic cells, then, are capable of restoring contractile activity of dysgenic myotubes in vitro, suggesting that a non-specific mechanism is involved in the phenotypic reversion of affected muscle cells. The restoration process seems to imply a close relationship between myotubes and normal glial cells.

Animals↗
PubMed1995

Inhibition of proliferation in 8-week-old mdx mouse muscle fibroblasts in vitro.

Our purpose is to understand why mdx muscle does not show the progressive degeneration observed in human Duchenne muscular dystrophy (DMD) muscle. In the mouse, the regenerative process compensates for the necrosis of the muscle fibers, particularly during the acute phase of the disease (5-9 weeks). In DMD muscle, there is a gradual failure of the regenerative process and the muscle fibers are replaced by connective and fatty tissue. We propose that distinct properties of mdx and DMD muscle fibroblasts could be one of the reasons for the differences between the mdx and DMD phenotypes. We found that fibroblasts taken from human DMD and control muscle had similar in vitro proliferative capacities. The proliferation rate of mouse muscle fibroblasts decreased during the acute phase of the disease, and inhibition was complete in fibroblasts from 8-week-old mdx mice. Moreover, the medium conditioned by these cells inhibited fibroblast proliferation. The effect was specific for fibroblasts, since this conditioned medium stimulated myoblast proliferation, as did control fibroblast-conditioned medium. These results suggest that 8-week-old mdx mouse muscle fibroblasts produce an inhibitor of their own proliferation and a growth factor specific for myoblasts in vitro. If these factors are secreted in vivo, the growth inhibitory factory may stop fibroblast proliferation whereas the mitogenic activity could stimulate satellite cell proliferation, thus favouring muscle regeneration.

Adolescent↗
PubMed1995

Facilitation of thin-layer chromatographic identification of opiates by derivatization with acetic anhydride or methoxyamine.

Qualitative identification of opiates in urine is commonly achieved in two stages, the first involving immunoassay screening and the second involving chromatographic confirmation. Identification of specific opiates is often requested to determine whether the source of opiates is from diet, prescription pharmaceuticals, or illicit drugs. During evaluation of the Toxi-Lab thin-layer chromatographic system as a confirmatory technique for urinary opiates, we encountered difficulty distinguishing opiates with similar retention factor values and colorimetric behavior. By exploiting chemical differences of the comigrating opiates through preparation of acetate or methoxime derivatives, followed by chromatography of the underivatized and derivatized samples in adjacent lanes, we were able to more easily distinguish codeine from hydrocodone, 6-acetylmorphine from oxymorphone, and dihydrocodeine from hydromorphone.

Acetic Anhydrides↗
PubMed1995

Spatial and temporal distribution of [Ca2+]i in normal human myotubes. A fura-2 imaging study.

The spatio-temporal distribution of intracellular, free calcium ions, [Ca2+]i, induced in human myotubes by electrical stimulation typically showed a relatively large increase of [Ca2+]i in the vicinity of the plasmalemma. The similarity of this distribution, with that observed after the application of caffeine, and the lack of any effect of lanthanum, strongly suggest that the main source of Ca2+ participating in the electrically induced transient is the sarcoplasmic reticulum. Aneurally cultured human myotubes therefore display a 'skeletal muscle type' coupling between membrane depolarization and calcium release. However, the relatively slow time course of the electrically induced transients compared to rat and mouse myotubes, together with the inability of Ca2+ released from the sarcoplasmic reticulum to activate the contractile machinery, implies that aneurally cultured human myotubes achieve only a limited degree of differentiation. The relevance this may have to an apparent delay between the electrically induced rise in intranuclear Ca2+ relative to cytosolic Ca2+ remains to be determined but, at this stage of differentiation, there appears to be some form of barrier to free diffusion between the two cellular compartments.

Caffeine↗
PubMed1994

Assessing the validity of the updated Medical College Admission Test.

This report represents early information about the validity of the updated Medical College Admission Test (MCAT) battery introduced in 1991. Data are given on both the use of the new examination in the selection of medical students and its estimated predictive value for freshman students' performance. Admission officials from 114 institutions responded to a survey on medical school admission practices and on the use of MCAT data; also elicited were assessments of the examination in relation to its design and implementation objectives. Regression-based evaluations of the predictive validity of the MCAT, undergraduate grades, and of undergraduate selectivity data for first-year grades at 12 institutions are described. Survey responses suggest that MCAT data are viewed in relation to the varied information needs of admission decision making and are supplemented by other academic and nonacademic information in selection. The new battery generally is judged favorably by admission officials. Predictive validity results reflect the usefulness of MCAT scores, undergraduate grades, and selectivity data for identifying individuals apt to succeed in medical school. The authors conclude that preliminary information about the results of the new examination is encouraging. The members of the MCAT Validity Studies Advisory Group, who assisted the authors in framing and conducting the research presented in this report, continue their research and deliberations about the use, utility, and impact of the updated MCAT.

College Admission Test↗
PubMed1993

Effect of sera from myasthenia gravis patients and of alpha-bungarotoxin on acetylcholinesterase during in vitro neuromuscular synaptogenesis.

Myasthenia gravis (MG) is mediated by circulating antibodies directed against acetylcholine receptor (AChR) but the antibody titre is poorly correlated with the clinical severity of the disease. We analysed acetylcholinesterase (AChE) activity, molecular forms and distribution during in vitro synaptogenesis, in the presence of sera from MG patient. We observed that the formation of AChE patches is inhibited in proportion to the anti-AChR antibody titre, whatever the clinical severity of the disease. The total activity and the proportion of the different molecular forms were unchanged suggesting that AChE level and distribution are controlled by independent mechanisms. To clarify the relationship between the mechanisms of AChE concentration during synaptogenesis and AChR concentration, we compared the effect of MG sera (receptors are internalised and degraded) and of the acetylcholine antagonist alpha-bungarotoxin (non-functional receptors are still present in the muscular membrane). In the presence of alpha-bungarotoxin, the number of AChR clusters, and AChE activity and concentration were equivalent to control values. The comparison of the results obtained with antibodies and alpha-bungarotoxin suggests that the presence and/or concentration of AChR is a necessary condition for normal concentration of AChE during synaptogenesis.

Acetylcholinesterase↗
PubMed1993

[Effect of the mutation muscular dysgenesis on the mitochondrial metabolism of fibroblasts in vitro].

Muscular dysgenesis is a lethal mutation characterized by an absence of striated muscle contraction. This abnormality of function caused by a defect in excitation-contraction coupling is due to the lack of the alpha 1 subunit from the dihydropyridine receptor in the transverse tubule membrane. A phenotypical reversion is obtained in vitro by addition of normal cells, as fibroblasts, in dysgenic muscle culture. Perisynaptic fibroblasts from denervated muscle have been shown to synthetize molecules which are usually concentrated at the synapses suggesting that signal arising after denervation may influence fibroblasts synthesis ability. We show here that the energetic metabolism level from dysgenic fibroblast is lower than that from normal fibroblasts. The synthesis or the release of muscular signals that are involved in fibroblast differentiation could be disturbed in mdg/mdg myotubes.

Electron Transport↗
PubMed1991

The effect of tetanus toxin on in vitro synaptogenesis.

Cultures of spinal cord neurons and cocultures of rat embryo neurons and muscle cells have been studied in the presence of tetanus toxin (TT) at a concentration of 40 micrograms/ml of medium. TT strongly stimulated neurite outgrowth, notably branching from the cell bodies. In addition it induced a marked, overall increase in acetylcholine receptor (AChR), but inhibited focalisation of AChR and acetylcholinesterase (AChE) at the synaptic sites. TT seems to act on neurite emergence, on the neuronal factor(s) controlling AChE and AChR concentrations, and on the factor(s) modulating degradation and/or synthesis of AChR.

Acetylcholinesterase↗
PubMed1991

Fura-2 imaging of spontaneous and electrically induced oscillations of intracellular free Ca2+ in rat myotubes.

Rat myotubes have a resting [Ca2+]i of about 82 nM. Myotubes 3-5 days old (quiescent myotubes) display electrically induced and spontaneous transients in the intracellular concentration of free Ca2+ ions ([Ca2+]i) uncoupled to any detectable contraction. By contrast, 1- to 2-day-old myotubes are insensitive to electrical stimuli and, after 6 days in culture, stimulated myotubes always show [Ca2+]i transients and twitch contractions. The spatial distribution of [Ca2+]i variations in quiescent myotubes is heterogeneous, local increases in [Ca2+]i being mainly observed near the periphery of the cell. The small effect of different external Ca2+ concentrations and of Cd2+ on the amplitude of the [Ca2+]i oscillation indicates that the main source of Ca2+ may be the sarcoplasmic reticulum. This conclusion is supported by the close similarity between electrically induced and caffeine-induced [Ca2+]i maps. These findings suggest that, at an early stage of myotube ontogenesis, a part of the excitation/contraction coupling, as membrane ionic channels, voltage sensors and Ca2+ release and reuptake mechanisms, is functional but, apparently, still uncoupled to the contractile machinery.

Animals↗
PubMed1990

Neurite outgrowth and proliferation of non-neuronal cells on cryostat sections of adult muscle.

Rat spinal cord cells were cultured on cryostat sections of innervated and denervated muscle. Neurite outgrowth was greater on sections of denervated muscle, which therefore appeared to act on in vivo nerve regeneration. It seems that muscle sections were able to release into the culture medium factors that increase proliferation of fibroblasts. The muscle therefore appeared able to modulate its interaction with its environment by acting on different types of cells.

Animals↗
PubMed1990

A quantitative assessment of respiratory patterns and their effects on dentofacial development.

The purpose of this study was to assess the effects of quantitatively determined breathing patterns on dentofacial development in growing children. Forty-nine subjects ranging in age from 10 to 16 years participated in the breathing pattern assessment portion of this project. Oral, nasal, and total airflow were measured at separate times by means of a head-out body plethysmograph technique and the values were compared with the subjects' and parents' subjective perceptions of their breathing modes. These breathing pattern measurements also were compared to nasal airway resistance and nasal power. Temporal variation and cyclic respiration, which may play important roles in quantitative evaluations of childrens' breathing patterns, also were addressed. In addition, objective assessments of possible associations between dentofacial structure and respiration were made on 45 of these children. Most subjects' exhibited was either an oronasal or a completely nasal respiratory pattern. However, significant variation in breathing measures was evident among a number of subjects whose breathing was measured twice on the same day and on different days. No significant correlations were found between objectively measured and subjectively determined impressions of respiratory patterns. In addition, there was no association between nasal airway resistance or nasal power and plethysmograph recordings of percent of mouth breathing. Comparisons of measured breathing modes and dentofacial characteristics revealed a weak tendency among mouth breathers toward a Class II skeletal pattern and retroclination of maxillary and mandibular incisors. In contrast, subjective perception of mouth breathing was associated with increased anterior facial height and greater mandibular plane angles. Nasal power and resistance were not correlated with either dental or skeletal variables. This study presents evidence that determination of respiratory pattern is a complex issue for which methods must be refined and performed longitudinally.

Adolescent↗
PubMed1990

Acetylcholinesterase in cocultures of rat myotubes and spinal cord neurons: effects of collagenase and cis-hydroxyproline on molecular forms, intra- and extracellular distribution, and formation of patches at neuromuscular contacts.

Cultures of rat myotubes from 18-day-old embryos produce both globular (G) and asymmetric (A) forms of acetylcholinesterase (AChE; EC 3.1.1.7), mostly G1, G4, and A12 and a small proportion of A8. We show that all forms are partly intracellular and partly exposed to the extracellular medium; the A forms and their intra- and extracellular distribution are not modified when myotubes are grown in the presence of spinal cord neurons. In these cocultures, however, AChE patches may be detected immunohistochemically at sites of neuromuscular contacts. These patches represent a very minor proportion of AChE activity. We found that collagenase removes AChE patches but not the acetylcholine receptor clusters with which they coincide. This digestion specifically decreases the level of the A12 form. cis-Hydroxyproline, an inhibitor of collagen synthesis, reduces the level of G1 and blocks the synthesis of A forms.

Acetylcholinesterase↗
PubMed1989

In vitro synaptic maturation.

Cocultures of spinal cord neurons and muscle cells taken from rat embryos were used for in vitro reproduction of embryonic synapses. This system did not display the synaptic maturation characteristics of postnatal development: decreased multiple innervation and the presence of a developed subneural apparatus. Studies on cultures consisting of 3 cell types (muscle cells, nerve cells, Schwann cells), or on co-cultures (muscle cells, nerve cells), in the presence or absence of a monoclonal antibody directed against an antigen from Schwann cells, have shown that Schwann cells participate in synaptic maturation and in the elimination of superfluous synapses. The synapses were visualised for optical microscopy by co-localisation of acetylcholinesterase (AChE) spots and acetylcholine receptor (AChR) clusters.

Animals↗