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L Dux

Publications and source records attributed to L Dux.

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

The loss of pacing-induced preconditioning in atherosclerotic rabbits: role of hypercholesterolaemia.

A brief rapid pacing has been shown to protect rabbit heart against global myocardial ischaemia induced by subsequent longer pacing. We studied whether pacing-induced preconditioning was reproducible in experimental hypercholesterolaemia. In conscious rabbits with an implanted right ventricular electrode and left ventricular polyethylene catheters, pacing of 500 bpm over 20 min induced an intracavitary ST-segment elevation of 3.2 +/- 0.41 mV, shortened ventricular effective refractory period and increased left ventricular end-diastolic pressure from prepacing 105 +/- 3.9 ms and 4.0 +/- 0.93 mmHg to post-pacing 62 +/- 6.4 ms and 27.9 +/- 7.2 mmHg, respectively. A 10-min preconditioning pacing followed by a 5-min interval markedly attenuated these test pacing-induced ischaemic changes. Rabbits were fed a cholesterol-enriched diet over 4, 8 and 12 weeks, responded to a 5- or 10-min pacing with ischaemic changes of the same degree as did controls to a 10- or 20-min pacing, respectively. A 4-week diet elevated total serum cholesterol from 1.7 +/- 0.4 to 24.1 +/- 2.9 mmol/l without apparent atherosclerotic lesions in the thoracic aorta assessed by Oil-Red O staining and planimetry, but it abolished protection induced by a 5-min preconditioning pacing. A 12-week diet increased serum cholesterol and lesion surface area to 26.9 +/- 3.2 mmol/l and 89.6 +/- 6.4%, respectively, and continued to block preconditioning. When these animals were refed normal chow over additional 6 weeks, serum cholesterol level dropped to 2.6 +/- 0.80 mmol/l with no change in atherosclerotic lesions, the preconditioning effect, however, recovered. We conclude that hypercholesterolaemia blocks preconditioning irrespective of the development of atherosclerosis.

Animals↗
PubMed1995

Ventricular overdrive pacing-induced preconditioning and no-flow ischemia-induced preconditioning in isolated working rat hearts.

To examine preconditioning induced by short periods of ventricular overdrive pacing (VOP) as compared with that induced by no-flow ischemia, we subjected isolated working rat heart to 10-min coronary artery occlusion (test ischemia) followed by 3-min reperfusion after three intermittent periods of VOP (10 Hz) or 5-min no-flow ischemia, respectively. In the nonpreconditioned group, coronary occlusion decreased aortic flow (AF) from 46.6 +/- 2.4 to 13.7 +/- 1.7 ml/min and increased left ventricular end-diastolic pressure (LVEDP) from 0.53 +/- 0.05 to 2.02 +/- 0.07 kPa. Preconditioning by VOP or no-flow ischemia significantly increased AF to 25.1 +/- 2.3 ml/min (p < 0.001) and to 27.3 +/- 1.4 ml/min (p < 0.001) and decreased LVEDP to 1.38 +/- 0.1 kPa (p < 0.001) and to 1.65 +/- 0.05 kPa (p < 0.05), respectively, after test ischemia. Glibenclamide 10(-7) M which blocked the anti-ischemic effect of the ATP-sensitive K(+)-channel (KATP) opener cromakalim, inhibited VOP-induced protection (AF 20.3 +/- 2.3 ml/min; LVEDP 1.82 +/- 0.15 kPa), but did not affect no-flow ischemia-induced preconditioning [AF 26.6 +/- 2.4 ml/min (p < 0.001), LVEDP 1.60 +/- 0.07 kPa (p < 0.01)]. VOP and no-flow ischemia precondition heart, however their cardioprotective mechanisms may be different in terms of KATP activation in rats.

Animals↗
PubMed1995

Nitroglycerin-induced direct protection of the ischaemic myocardium in isolated working hearts of rats with vascular tolerance to nitroglycerin.

We investigated whether nitroglycerin (NTG) was able to produce an anti-ischaemic effect in isolated working hearts of rats with vascular tolerance to NTG. Hearts isolated from tolerant and non-tolerant rats were subjected to 10 min coronary occlusion in the presence of 10(-7) M NTG and/or its solvent. NTG alleviated ischaemia-induced deterioration of cardiac function and decreased lactate dehydrogenase release whilst having no effect on coronary flow nor the area of the ischaemic zone both in hearts isolated from NTG-tolerant and non-tolerant rats. The magnitude of the effect was similar in the two groups. These results suggest that the anti-ischaemic effect of NTG involves direct myocardial mechanisms independent of its vascular action and that vascular tolerance to NTG does not affect this direct protective action.

Animals↗
PubMed1994

Experimental regeneration in canine muscular dystrophy--2. Expression of myosin heavy chain isoforms.

The sequential expression of neonatal, fast and slow myosin heavy chain isoforms was examined during the regeneration of normal and dystrophic dog muscle from 1 to 56 days, following necrosis induced by the venom of Notechis scutatis, to assess the regenerative potential of dystrophic muscle. Regeneration was equally rapid in normal and dystrophic dogs but morphological and immunocytochemical abnormalities were more apparent in the dystrophic fibres. New myotubes were formed by 3 days, and by 4 days all myosin isoforms were expressed. Neonatal myosin persisted in normal dogs after morphological restoration of the muscle and after dystrophin and beta-spectrin expression had returned to normal. Neonatal myosin was considerably reduced by 21 days in normal dogs, but persisted beyond 28 days in dystrophic dogs, suggesting a delay in maturation. At 42 and 56 days, dystrophic dogs showed a population of small fibres expressing neonatal myosin, which may represent a second cycle of degeneration and regeneration. The reciprocal pattern of fast and slow myosin was not fully restored in normal or dystrophic regenerating muscle, and co-expression persisted. Thus, dystrophic muscle retains its potential to regenerate, but maturation is slower than normal. The persistent co-expression of isoforms has implications for the long-term function of fibres formed after myoblast therapy, but the results imply that a stable state can be achieved if dystrophin expression is restored by gene or myoblast transfer therapy.

Animals↗
PubMed1994

Expression of utrophin (dystrophin-related protein) during regeneration and maturation of skeletal muscle in canine X-linked muscular dystrophy.

The regulation of utrophin, the autosomal homologue of dystrophin, has been studied in the canine X-linked model of Duchenne muscular dystrophy. Dystrophic muscle has been shown to exhibit abnormal sarcolemmal expression of utrophin, in addition to the normal expression at the neuromuscular junction, in peripheral nerves, vascular tissues and regenerating fibres. To establish whether this abnormal presence of utrophin in dystrophic muscle is a consequence of continued expression following regeneration, or is attributable to a disease related up-regulation, the expression of utrophin was compared immunocytochemically with that of dystrophin, beta-spectrin and neonatal myosin in regenerating normal and dystrophic canine muscle, following necrosis induced by the injection of venom from the snake Notechis iscutatis. In normal regenerating muscle, sarcolemmal utrophin and dystrophin were detected concomitantly from 2-3 d post-injection, prior to the expression of beta-spectrin. Down-regulation of utrophin was apparent in some fibres from 7 d, and it was no longer present on the extra-junctional sarcolemma by 14 d. Neonatal myosin was still present in all fibres at this stage, but dystrophin and beta-spectrin had been fully restored. In dystrophic regenerating muscle, down-regulation of utrophin occurred from 7 d, although it persisted on some fibres until 28 d, longer than in normal muscle. At 42 d, however, utrophin in dystrophic muscle was only detected in a population of small fibres thought to represent a second cycle of regeneration, with no immunolabelling of mature fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Notechis scutatus venom increases the yield of proliferating muscle cells from biopsies of normal and dystrophic canine muscle--a possible source for myoblast transfer studies.

The injection of 1 micrograms Notechis scutatus (Australian tiger snake) venom (notexin) induces localized necrosis in the muscles of normal and dystrophic dogs. Biopsies taken from the muscles on the second day of postnecrotic regeneration provide about 8-16 x 10(6) cells capable of proliferation per g tissue, about 100 fold more than the untreated adult dog muscles. Muscle specific markers, such as the capacity of the cells to fuse, surface labelling with N-CAM antibodies (Leu-19 and 5.1.H11), and immunostaining with desmin, indicated that over 90% of the cultivated cells are indeed myogenic. The method is a safe and cost effective way to generate large amounts of proliferating muscle cells from biopsies of adult animals, which could provide a useful step in the therapeutic efforts in inherited muscle diseases by the implantation of normal myoblasts or genetically corrected myoblasts.

Animals↗
PubMed1992

Time-dependent increases in Na+,K(+)-ATPase content of low-frequency-stimulated rabbit muscle.

Chronic low-frequency stimulation of rabbit fast-twitch muscle induced time-dependent increases in the concentration of the sarcolemmal Na+,K(+)-ATPase and in mitochondrial citrate synthase activity. The almost twofold increase in Na+,K(+)-ATPase preceded the rise in citrate synthase and was complete after 10 days of stimulation. We suggest that the increase in Na+,K(+)-ATPase enhances resistance to fatigue of low-frequency-stimulated muscle prior to elevations in aerobic-oxidative capacity.

Animals↗
PubMed1992

Metabolite patterns related to exhaustion, recovery and transformation of chronically stimulated rabbit fast-twitch muscle.

Rabbit fast-twitch tibialis anterior muscle was subjected to chronic low-frequency stimulation (10 Hz, 24 h/day). Measurements of the time course of changes in the concentration of metabolites of energy metabolism were performed in order to test the hypothesis whether or not alterations in the metabolite profile might represent possible signals for triggering muscle fibre type transformation. Most of the investigated metabolites displayed triphasic changes in response to persistently increased contractile activity. During the first 15 min of stimulation, drastic reductions were observed for adenosine triphosphate (ATP, 56%), phosphocreatine (PCr, 60%) and glycogen (76%), as well as 3- to 4-fold and 10-fold increases for glucose and lactate, respectively. This early metabolic perturbance coincided with a rapid reduction of isometric force. The next phase, extending to 4 days of stimulation, was characterized by a nearly complete recovery of ATP and PCr, and an overshoot in glycogen. The first signs of metabolic recovery were already detectable in 60-min-stimulated muscle when isometric force was still markedly depressed. These results demonstrated an impressive capability of the muscle to recover with ongoing stimulation from an initial, dramatic disturbance in energy metabolism. During the final phase, extending to 50 days, the metabolite profile approached that of a slow-twitch muscle with moderate reductions in total adenine nucleotides, ATP, total creatine, PCr and glycogen. A conspicuous result was the finding that, contrary to the recovery of most metabolites, the ratio of ATP to the product of free adenosine diphosphate and resting free inorganic phosphate was persistently depressed with ongoing stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗
PubMed1992

Different sensitivity of the sarcoplasmic reticulum Ca(2+)-ATPase enzyme to fluorescein-isothiocyanate in rabbit and carp muscles.

1. Carp and rabbit sarcoplasmatic reticulum Ca(2+)-ATPase enzymes were compared with respect to their sensitivity to FITC labelling. 2. The carp enzyme showed much lower sensitivity to FITC in the Ca(2+)-Mg2+ activated ATPase activity. Fifty percent inhibition was observed at 20 microM labelling FITC concentration; in rabbit enzyme this inhibition was already achieved at 2 microM FITC. 3. The tryptic cleavage products of the carp enzyme identified with immunoblot analysis as well as with FITC fluorescence, suggest multiple cleavage, yielding different fragments from the ones well known in rabbit and in rat enzyme. 4. The present results indicates major structural differences with respect to the FITC binding, and tryptic cleavage between the SR Ca(2+)-ATPase enzymes from carp and rabbit, despite the cross-reactivity with polyclonal antibodies.

Animals↗
PubMed1992

Experimental regeneration in canine muscular dystrophy--1. Immunocytochemical evaluation of dystrophin and beta-spectrin expression.

The expression of dystrophin and beta-spectrin was examined from 1 to 56 days in regenerating muscle fibres in normal and dystrophic dogs, following necrosis induced by the venom of Notechis scutatis. Normal and dystrophic dog muscle regenerated at an equal rate and new myotubes were present in both at the periphery of necrotic fibres by 3 days. In normal dogs dystrophin was detected in the sarcoplasm of the regenerating fibres by 3 days and was localized to the plasma membrane by 4 days. The localization of dystrophin is independent of beta-spectrin and was detected before beta-spectrin, which was not observed until 5-6 days. Normal peripheral labelling of both was restored by 14 days in normal dogs. Normal beta-spectrin labelling of regenerating dystrophic fibres was also restored by 14 days and is not dependent on the presence of dystrophin in dystrophic dogs. A proportion of regenerating fibres in normal and dystrophic dogs showed weak immunolabelling of beta-spectrin prior to 14 days. This is a feature of immature muscle fibres. Antibodies to different domains of dystrophin bound to the periphery and sarcoplasm of regenerating fibres in dystrophic dogs, particularly during the first 7 days of regeneration, but the fluorescence was less intense than in normal dogs. Weak labelling with antibodies corresponding to the C-terminus of the rod domain of dystrophin persisted on dystrophic regenerating fibres up to 21 days. This may relate to developmental isoforms of dystrophin.

Animals↗
PubMed1991

Separation of active and inactive (nonphosphorylating) Ca(2+)-ATPase in sarcoplasmic reticulum subfractions from low-frequency-stimulated rabbit muscle.

Chronic low-frequency stimulation elicits in rabbit fast-twitch muscle a partial inactivation of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase and Ca(2+)-uptake activities. Inactive Ca(2+)-ATPase was enriched in a light microsomal fraction by sucrose density gradient centrifugation after calcium oxalate loading in the presence of ATP. This fraction showed a reduced specific activity and phosphoprotein formation of the Ca(2+)-transport ATPase. These results suggest that the inactivation of the Ca(2+)-ATPase as induced by increased contractile activity, is confined to a specific SR vesicle population.

Animals↗
PubMed1990

Chronic low-frequency stimulation of rabbit fast-twitch muscle induces partial inactivation of the sarcoplasmic reticulum Ca2(+)-ATPase and changes in its tryptic cleavage.

Persistently increased contractile activity as induced by low-frequency stimulation in fast-twitch rabbit muscle elicits a partial inactivation of the sarcoplasmic reticulum Ca2(+)-ATPase function with regard to Ca2+ transport and ATP hydrolysis. Electron microscopy showed no differences in the frequency and structure of the two-dimensional Ca2(+)-ATPase crystals between microsomal fractions from normal and stimulated muscles. However, differences existed between the tryptic digestion of the Ca2(+)-ATPase in both the membrane-bound and solubilized enzyme at the first tryptic cleavage site, named T1 (Arg505). This followed from a delayed appearance of the A and B fragments of the Ca2(+)-ATPase in the electrostimulated muscle. No differences existed with regard to the second tryptic cleavage site, named T2 (Arg198). Confirming previous results, fluorescein isothiocyanate (FITC) binding to the enzyme of the chronically stimulated muscle was markedly reduced. The FITC-labeled fraction of the enzyme from both the normal and the stimulated muscle followed similar time courses of tryptic cleavage. The fraction of Ca2(+)-ATPase that did not bind TITC was identified by immunoblot analysis as the trypsin-resistant form. In view of the vicinity of T1, the FITC- and the ATP-binding sties, these results point to a modification of the enzyme in that region leading to an inactivation of about 50% of the sarcoplasmic reticulum Ca2(+)-ATPase molecules.

Animals↗
PubMed1990

Dexamethasone treatment attenuates the development of ischaemic brain oedema in gerbils.

Transient global forebrain ischaemia was produced in Mongolian gerbils by occluding both common carotid arteries for 10 min followed by 48 h recirculation. Dexamethasone, 5 mg/kg i.p., was given 5 h before the occlusion and every 12 h thereafter. After occlusion an increase in water, sodium and calcium content was found in the parietal cortex and hippocampus, while the concentration of potassium decreased. Exudation of plasma albumin was not found in the brain. The activity of Na+, K(+)-ATPase decreased in the hippocampus. Morphological signs of cerebral oedema were also observed, both in the CA1 region of the hippocampus and in the cortex. Dexamethasone treatment prevented the accumulation of water, sodium and calcium in the ischaemic brain. It also attenuated the oedematous morphological changes of the blood-brain barrier. Thus dexamethasone treatment may also have therapeutic relevance in the acute, high-risk phase of patients suffering from repetitive, transitoric cerebral ischaemia.

Animals↗
PubMed1990

Saturation transfer electron spin resonance of Ca2(+)-ATPase covalently spin-labeled with beta-substituted vinyl ketone- and maleimide-nitroxide derivatives. Effects of segmental motion and labeling levels.

The Ca2(+)-ATPase in native sarcoplasmic reticulum membranes was selectively spin-labeled for saturation transfer electron spin resonance (ESR) studies by prelabeling with N-ethylmaleimide and by using low label/protein ratios. Results with the nitroxide derivative of the standard sulphydryl-modifying reagent, maleimide, were compared with a series of six novel nitroxide beta-substituted vinyl aryl ketone derivatives which differed (with two exceptions) in the substituent at the ketone position. The two exceptions had a different electron withdrawing group at the alpha-carbon, to enhance further the electrophilic character of the beta-carbon. Although differing in their reactivity, all the conjugated unsaturated ketone nitroxide derivatives displayed saturation transfer ESR spectra indicative of much slower motion than did the maleimide derivative. The saturation transfer ESR spectra of maleimide-labeled Ca2(+)-ATPase therefore most likely contain substantial contributions from segmental motion of the labeled group. The effects of the level of spin labeling were also investigated. With increasing degree of spin label incorporation, the linewidths of the conventional ESR spectrum progressively increased and the intensity of the saturation transfer spectrum dropped dramatically, as a result of increasing spin-spin interactions. The hyperfine splittings of the conventional spectrum and the outer lineheight ratios of the saturation transfer spectrum remained relatively unchanged. Extrapolation back to zero labeling level yielded comparable values for the effective rotational correlation times deduced from the saturation transfer spectrum intensities and from the lineheight ratios, for the vinyl ketone label. For the maleimide label the extrapolated values from the integral are significantly lower than those from the lineheight ratios, probably because of the segmental motion. Comparison is made of the effective rotational correlation time for the vinyl ketone label with the predictions of hydrodynamic models for the protein diffusion, in a discussion of the aggregation state of the Ca2(+)-ATPase in the native sarcoplasmic reticulum membrane. The implications for the study of protein rotational diffusion and segmental motion, and of the proximity relationships between labeled groups, using saturation transfer ESR spectroscopy are discussed.

Animals↗
PubMed1990

Sarcoplasmic reticulum (SR) Ca2(+)-ATPase as a marker of muscle cell differentiation: immunohistochemical investigations of rhabdomyosarcomas and enhancement of the immunostaining after sodium methoxide pretreatment.

An immunocytochemical investigation of sarcoplasmic reticulum (SR) Ca2(+)-ATPase (SR-Ca-ATPase) was performed on formalin-fixed paraffin-embedded specimens of different types of rhabdomyosarcomas such as variants of embryonal and pleomorphic forms. Immunostaining frequency of tumours using SR-Ca-ATPase was compared with that of traditionally used muscle specific markers myoglobin, and desmin. Utilizing the possible cleaving of ester bounds sodium methoxide pretreatment was found to be very effective in enhancement of SR-Ca-ATPase immunostaining reaction. In 11 of 15 tissue specimens of 5 cases round shaped and elongated rhabdomyoblasts with definite cytoplasm exhibited positive immunoreactions with all of the polyclonal antibodies tested, using the streptavidin-biotinylated peroxidase complex (S-ABC-method). In formalin-fixed and paraffin-embedded material of 2 cases of undifferentiated rhabdomyosarcomas composed of small round tumour cells with scanty cytoplasm pretreatment with sodium methoxide induced the immunostaining of SR-Ca-ATPase. After that pretreatment a staining of the paranuclear cytoplasm occurred in many of these undifferentiated tumour cells. In these 2 cases, neither myoglobin nor desmin antibodies could react. However, when frozen sections of one of the poorly differentiated tumours were used monoclonal and polyclonal desmin antibodies reacted immunocytochemically in all of the small cells. Sodium methoxide induced or enhanced SR-Ca-ATPase immunocytochemical reaction can be a further addition to the diagnosis of rhabdomyosarcomas in formalin-fixed paraffin-embedded sections, even when desmin antibody fails to react.

Antibodies, Monoclonal↗
PubMed1990

The effect of membrane potential on the limited tryptic digestion of the sarcoplasmic reticulum Ca(2+)-ATPase.

The tryptic cleavage process of the sarcoplasmic reticulum Ca(2+)-ATPase was analysed under the influence of experimentally generated membrane potential. The digestion of the Ca2+ transport enzyme was stopped before the dissipation of the potential response. The cleavage products reflected the actual conformation of the enzyme as the low Ca2+ affinity E2, under the influence of inside positive, and as the high Ca2+ affinity E1 conformation under the influence of inside negative potential. These results provide further support for the possible role of transient membrane potential changes in the regulation of the conformational equilibrium of the sarcoplasmic reticulum Ca2+ pump enzyme.

Animals↗