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Biomedical subjects

M Peckham

Publications and source records attributed to M Peckham.

At least 37 records · Page 2Linked to original sources
PubMed1994

Myogenic cell lines derived from transgenic mice carrying a thermolabile T antigen: a model system for the derivation of tissue-specific and mutation-specific cell lines.

Skeletal myoblasts cloned from limb muscles of H-2Kb-tsA58 transgenic mice remained proliferative through at least 80 generations under conditions permissive for expression and function of the tsA58 gene product. When switched to nonpermissive conditions or implanted into muscles of nude mdx mice they underwent differentiation but, in one clonal cell line, a small proportion appeared to become quiescent muscle precursors in vivo. H-2Kb-tsA58 X mdx/mdx F1 male mice yielded dystrophin-deficient myoblasts. By such simple genetic crosses, H-2Kb-tsA58 transgenic mice provide a valuable tool for the rapid isolation of cell lines, myogenic or otherwise, bearing mutations of interest.

Animals↗
PubMed1994

A birefringence study of changes in myosin orientation during relaxation of skinned muscle fibers induced by photolytic ATP release.

The birefringence of isolated skinned fibers from rabbit psoas muscle was measured continuously during relaxation from rigor produced by photolysis of caged ATP at sarcomere length 2.8-2.9 microns, ionic strength 0.1 M, 15 degrees C. Birefringence, the difference in refractive index between light components polarized parallel and perpendicular to the fiber axis, depends on the average degree of alignment of the myosin head domain with the fiber axis. After ATP release birefringence increased by 5.8 +/- 0.7% (mean +/- SE, n = 6) with two temporal components. A small fast component had an amplitude of 0.9 +/- 0.2% and rate constant of 63 s-1. By the completion of this component, the instantaneous stiffness had decreased to about half the rigor value, and the force response to a step stretch showed a rapid (approximately 1000 s-1) recovery phase. Subsequently a large slow birefringence component with rate constant 5.1 s-1 accompanied isometric force relaxation. Inorganic phosphate (10 mM) did not affect the fast birefringence component but accelerated the slow component and force relaxation. The fast birefringence component was probably caused by formation of myosin.ATP or myosin.ADP.Pi states that are weakly bound to actin. The average myosin head orientation at the end of this component is slightly more parallel to the fiber axis than in rigor.

Adenosine Triphosphate↗
PubMed1991

Protein engineering and the study of muscle contraction in Drosophila flight muscles.

We describe an experimental approach to the use of genetics to study muscle contraction in Drosophila melanogaster. Mutations induced by in vitro mutagenesis are inserted into the genome of flies using P-element mediated transformation, permitting the effects of the mutant genes to be studied in vivo in the indirect flight muscles (IFMs). Details of how mechanical experiments can be performed on skinned IFMs, despite their small size, are provided. The effects of two in vitro actin mutations, G368E and E316K, are described. The problems of performing biochemical and biophysical experiments on the IFMs and their myofibrillar proteins are described, together with indications as to how these may be overcome.

Actins↗
PubMed1990

Alteration in crossbridge kinetics caused by mutations in actin.

The generation of force during muscle contraction results from the interaction of myosin and actin. The kinetics of this force generation vary between different muscle types and within the same muscle type in different species. Most attention has focused on the role of myosin isoforms in determining these differences. The role of actin isoforms has received little attention, largely because of the lack of a suitable cell type in which the myosin isoform remains constant yet the actin isoforms vary. An alternative approach would be to examine the effect of actin mutations, however, most of these cause such gross disruption of muscle structure that mechanical measurements are impossible. We have now identified two actin mutations which, despite involving conserved amino acids, can assemble into virtually normal myofibrils. These amino-acid changes in actin significantly affect the kinetics of force generation by muscle fibres. One of the mutations is not in the putative myosin-binding site, demonstrating the importance of long-range effects of amino acids on actin function.

Actins↗
PubMed1990

Physiological properties of the dorsal longitudinal flight muscle and the tergal depressor of the trochanter muscle of Drosophila melanogaster.

A prerequisite for using muscle mutants to study contraction in Drosophila melanogaster is a description of the mechanics of wild-type muscles. Here we describe the mechanics of two different wild-type muscles; the dorsal longitudinal flight muscle which is asynchronous (nerve impulses are not synchronised with each contraction), and a leg muscle, the tergal depressor of the trochanter, which is synchronous. We have compared their mechanics to those of the asynchronous flight and the synchronous leg muscle from the giant waterbug Lethocerus indicus. We found that the mechanics of the asynchronous flight muscles from the two species were similar. At rest length both muscles had a high relaxed stiffness, were partially activated by Ca2+ (low steady-state active tension) and, once activated, had a large delayed increase in tension, which was well maintained, in response to a rapid stretch. The rate constant for the delayed increase in tension was about 10 times greater for D. melanogaster than for L. indicus under the same conditions. The mechanics of the synchronous leg muscles from both species were different from those of the flight muscles and resembled those of other synchronous muscles such as vertebrate striated muscle. At rest length, both muscles had a lower relaxed stiffness than the flight muscles, were fully activated by Ca2+ (high steady-state active tension) and, once activated, had a small delayed increase in tension, which was less well maintained, in response to a rapid stretch. The rate constant for the delayed increase in tension was similar for the leg muscles of both species. The different mechanical properties of the flight and leg muscles must arise from differences in their contractile proteins. The demonstration that satisfactory mechanical responses can be obtained from the small (less than 1 mm long) muscles of D. melanogaster will enable future responses from mutant muscles to be tested.

Animals↗
PubMed1989

Myosin crossbridge orientation in demembranated muscle fibres studied by birefringence and X-ray diffraction measurements.

Muscle contraction is generally thought to involve changes in the orientation of myosin crossbridges during their ATP-driven cyclical interaction with actin. We have investigated crossbridge orientation in equilibrium states of the crossbridge cycle in demembranated fibres of frog and rabbit muscle, using a novel combination of techniques: birefringence and X-ray diffraction. Muscle birefringence is sensitive to both crossbridge orientation and the transverse spacing of the contractile filament lattice. The latter was determined from the equatorial X-ray diffraction pattern, allowing accurate characterization of the orientation component of birefringence changes. We found that this component decreased when relaxed muscle fibres were put into rigor at rest length, and when either the ionic strength or temperature of relaxed fibres was lowered. In each case the birefringence decrease was accompanied by an increase in the intensity of the (1,1) equatorial X-ray reflection relative to that of the (1,0) reflection. When fibres that had been stretched largely to eliminate overlap between actin- and myosin-containing filaments were put into rigor, there was no change in the orientation component of the birefringence. When isolated myosin subfragment-1 was bound to these rigor fibres, the orientation component of the birefringence increased. The birefringence changes at rest length are likely to be due to changes in the orientation of myosin crossbridges, and in particular of the globular head region of the myosin molecules. In relaxed fibres from rabbit muscle, at 100 mM ionic strength, 15 degrees C, the long axis of the heads appears to be relatively well aligned with the filament axis. When fibres are put into rigor, or the temperature or ionic strength is lowered, the degree of alignment decreases and there is a transfer of crossbridge mass towards the actin-containing filaments.

Adenosine Triphosphate↗
PubMed1989

A curriculum in oncology for medical students in Europe.

A curriculum in oncology for medical students in Europe is proposed. The proposals are presented with the unanimous approval of the deans of undergraduate medical schools and oncologists from 17 European countries who attended an EC/EORTC Workshop in Bonn in May 1988. The proposals arise as a response to the recognised deficiency of undergraduate cancer education in many medical schools and the pressing need to ensure that newly qualified doctors possess the necessary skills and knowledge to participate in cancer prevention, early diagnosis and curative and palliative management. The proposals concern both basic science and clinical practice, stressing the need for bedside teaching, instruction in the multi-disciplinary nature of cancer care and the elimination of bias towards particular disciplines. To achieve the objectives it is proposed that each medical school shall have an undergraduate teaching programme in oncology. A detailed prescription for an undergraduate curriculum is not attempted but rather a frame-work provided that should be adopted regardless of national and local differences in medical educational practice.

Curriculum↗
PubMed1988

Clinical aspects of metastases.

In the short term the major hope for reducing cancer mortality is to effect a reduction in the number of patients who develop malignant disease and in the proportion of cancer patients who present with metastases. Hitherto the major emphasis of clinical research on metastases has been directed at detection and elimination rather than prevention or early diagnosis. Extensive data relating histological class and tumour stage to risk of metastasis and metastatic pattern have been compiled from studies of relapse and from invasive and non-invasive staging procedures. However, the biological events involved in the metastatic process and the factors which influence it in relation to the natural history of primary human tumours are poorly understood. Information describing metastatic heterogeneity in individual patients, in terms of therapeutic response or intrinsic sensitivity to cytotoxic agents, is scanty. Similarly, the characteristics of human metastases in relation to the clonal heterogeneity of primary tumours are poorly defined. The clinical application of molecular biological techniques, which has led to the association of gene amplification with tumour behaviour in a range of sites, offers the prospects of improved tumour localization and therapy and, in the longer term, of tumour control by interventions based on a knowledge of the mechanisms that regulate cell growth and differentiation.

Clinical Protocols↗
PubMed1988

Testicular cancer.

Testicular cancer, which predominantly occurs in young men, has become increasingly common; it is presently the most common malignancy in men aged 20-34. Despite a lack of knowledge of aetiology, empirical advances, particularly in the management of patients with advanced disease, have been dramatic. Prior to the development of effective chemotherapy in the 1970s, less than 10% of men with metastatic non-seminomatous germ cell tumours were cured; nowadays approximately 90% of patients are potentially curable. The introduction of effective chemotherapy has led to a reappraisal of surgery and radiotherapy in the management of early stage disease and the introduction of a policy of surveillance in patients without evidence of metastases at the time of removal of the primary tumour. Following chemotherapy, surgery is required in approximately 25% of patients with advanced disease to excise residual masses, which in one-fifth of cases will show evidence of residual malignancy. In a proportion of patients, testicular cancer develops on a background of long-standing infertility, whereas in many men there is temporary oligospermia, despite a previous history of fertility. The majority of patients with prior evidence of spermatogenesis recover this function following chemotherapy and there is no evidence that children fathered by such patients have an increased risk of malformation. Despite physician optimism and excellent prospects for cure, significant psycho-social morbidity is associated with the diagnosis and treatment of testicular cancer. Factors contributing to this are being identified and will lead, hopefully, to the minimisation of such problems by appropriate intervention.

Adult↗
PubMed1988

Birefringence as a probe of crossbridge orientation in demembranated muscle fibres.

Birefringence measurements were used to investigate crossbridge orientation in demembranated muscle fibres of frog and rabbit. Birefringence depends on the interfilament spacing as well as on crossbridge orientation, so conditions were chosen such that changes in interfilament spacing were either eliminated or known from previous studies. At sarcomere length 2.3 micron there was a large birefringence decrease on putting relaxed fibres into rigor; at 3.7 micron this gave no change in birefringence. A simple model for crossbridge structure was used to interpret the birefringence data; it seems likely that reorientation of subfragment-1 (S-1) is responsible for the observed change. Decoration of rigor fibres with exogenous S-1 gave a birefringence increase corresponding to S-1 binding with its long axis at about 50 degrees to the fibre axis. The corresponding mean S-1 angle in relaxed muscle was estimated as about 35 degrees. When relaxation of rigor fibres was initiated by photolysis of caged-ATP in the absence of Ca2+ the birefringence increase showed two components, one 20 times faster than the other. The fast component was accompanied by a decrease of rapid stiffness, suggesting that it is caused by some crossbridges detaching to take up an orientation more parallel with the fibre axis. However the mechanical measurements indicated the presence of some active force generating crossbridges at this time, even in the absence of Ca2+, and these may also make a contribution to the fast birefringence component. Birefringence transients following ATP release in the presence of Ca2+ suggest that crossbridges are on average more perpendicular to the fibre axis during active force generation than in the rigor state.

Adenosine Triphosphate↗
PubMed1986

Labile heat and changes in rate of relaxation of frog muscles.

Observations were made of the labile heat and the progressive slowing of relaxation as a function of tetanus duration (Abbott effect) during isometric tetani of frog extensor longus digiti IV (e.l.d. iv) and sartorius muscle. Both the labile heat and slowing of relaxation are less marked in e.l.d. iv than in sartorius muscle. Both effects are depressed to the same extent in the second of two closely spaced tetani in sartorius muscle. The repriming of both effects follows the same time course in sartorius muscle. The hypothesis is discussed that both effects result from binding of calcium to parvalbumin during a tetanus, and that their repriming is due to the removal of calcium from parvalbumin by the sarcoplasmic reticulum.

Animals↗