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Biomedical subjects

N M De Clerck

Publications and source records attributed to N M De Clerck.

At least 19 recordsLinked to original sources
PubMed2005

In vivo assessment of emphysema in mice by high resolution X-ray microtomography.

High resolution X-ray microtomography (micro-CT) was used for the detection of emphysema in live mice. Emphysema was induced in C57BL/6 J mice by intratracheal instillation of different amounts of porcine pancreatic elastase. This emphysema could be clearly detected by micro-CT seven weeks post-treatment: analysis of the whole data set of virtual cross-sections showed the presence of a dose-dependent level of emphysema.

Animals↗
PubMed2003

Quantitative analysis of bone mineral content by x-ray microtomography.

A new non-destructive method based on x-ray microtomography (micro-CT) was developed to measure calcium density in bone. X-ray micro-CT was used as a quantitative approach to acquire and reconstruct virtual cross-sections through the sample. Accurate beam-hardening correction was implemented. Grey values in the virtual cross-sections were calibrated as calcium mineral density in bone. From these cross-sections, three-dimensional models were created. Calcium content was calculated directly from images and expressed as percentage per volume and per weight. Calcium mineral density was studied by this method in a unique set of bones isolated from newts (Pleurodeles waltlii Michah) that had travelled into space. A demineralization of 10% was shown as a consequence of sustained micro-gravity.

Animals↗
PubMed1991

Increased force levels after shortening and restretching skinned cardiac muscle.

At steady calcium activation, changes in loading conditions were imposed on single skinned cardiac myocytes and on multicellular skinned cardiac muscle. Despite the initial steady level of activation, an increase in isometric force (i.e. force gain) was observed after stretching following a period of shortening. Force gain was most pronounced at low levels of free activating calcium, but it was present at any level of free calcium, including maximal activation. The extent of shortening did not influence the amount of force gain. An increased level of shortening (i.e. shortening gain) was observed after clamping a single myocyte under afterloaded conditions. Since no membranous systems were present, the mechanism causing force and shortening gain were shown to be located at the level of the contractile proteins. The hypothesis is suggested that different steady states of the crossbridges could exist despite a constant steady level of calcium activation.

Animals↗
PubMed1988

Effects of ryanodine on relaxation in isolated myocardium from different animal species.

Relaxation in mammalian ventricular cardiac muscle is sensitive to the prevailing load. This "load dependence of relaxation" (LD) can be demonstrated only when an efficient sarcoplasmic reticulum (SR) is present. To define further the role of the SR in LD, we studied contraction and relaxation in cat, rat and frog cardiac muscle after exposure to ryanodine. Ryanodine is a selective inhibitor of calcium release from the SR. This view was confirmed in the present study in single cardiac rat myocytes with functioning SR. Ryanodine did not affect LD in multicellular mammalian myocardium even though it had already significantly depressed contractility, suggesting that calcium release from the SR plays no role in establishing LD. Calcium accumulation in the SR as a consequence of the inhibited release can account for the late depression of LD in the presence of ryanodine.

Alkaloids↗
PubMed1984

Uniform sarcomere behaviour during twitch of intact single cardiac cells.

Behaviour of sarcomere length was analysed in different regions of single cardiac cells (n = 249) of the ventricle, both at rest (n = 144) and during twitch contractions (n = 57). At rest, regional distribution of sarcomere length proved to be uniform. In the leaky cell (n = 48), resting sarcomere length was not affected over longer periods of time (up to 2 h), nor by lowering the ATP concentration (from 5 mM to 2.5 mM and 500 microM), nor by increasing free calcium within subactivating ranges (5, 20, 60 microM). No statistical differences could be detected between resting cell dimensions and sarcomere length between cells isolated from left and right ventricle (n = 64), nor between cells from epicardial or endocardial layers (n = 80). During twitch contraction in the intact unloaded cardiac cell (n = 32), sarcomere lengths in different regions were analysed every 20 ms and behaved synchronously, presenting arguments for uniformity during the myocardial contraction-relaxation cycle in the free-lying intact cardiac cell.

Animals↗
PubMed1981

Effect of temperature on the mechanical behaviour of single skinned cardiac cells.

The effect of changes in temperature (16-35 degrees C) on the contractile behaviour of single, skinned cardiac cells was analysed. Lowering the temperature decreased force development, extent of shortening and velocity of shortening. The effects of altering temperature on the calcium sensitivity of velocity of shortening were more pronounced than the temperature effect upon the calcium dependence of force and extent of shortening. At maximal activation force-velocity curves showed a marked shift in peak velocity, with hardly any effect on peak isometric force.

Animals↗
PubMed1981

Sarcomere distribution patterns in single cardiac cells.

Sarcomeres of single cardiac cells isolated either by microdissection or by enzymatic dissociation were visualized on a television screen, through the objective (63 X) of an inverted microscope and a television camera. A distinct line of the television picture was positioned on the preparation and the frequency content, corresponding to the dark and light areas of the striations was tracked by a phase-locked loop. This technique permitted the measurement of the length of successive sarcomeres and hence the sarcomere distribution pattern over the entire preparation.

Animals↗
PubMed1981

Relaxation properties of mammalian atrial muscle.

The properties of relaxation, particular the sensitivity of relaxation to load, were analyzed in isolated intact atrial muscle and in manually dissected, detergent-treated cellular preparations from cat, dog, and rat atria. Force and length traces under increasing afterloads and following load clamps were obtained using an electromagnetic lever-force transducer system for the intact muscles and a capacitance transducer system for the cellular preparations. In both types of preparations, the time course of relaxation was hardly affected by the load or by alterations in load (load clamps), unlike intact mammalian ventricular muscle. This load independence of relaxation, which was hardly influenced by variations of initial muscle length, resembled relaxation in intact frog ventricular muscle and in detergent-treated mammalian ventricular single cells. As relaxation of these ventricular preparations with poorly developed (frog) or absent (detergent-treated single cells) calcium-sequestering systems was shown to be governed by the dissipation of activation, these results suggest a similar control mechanism for relaxation in mammalian atrial muscle. Furthermore, load independence of relaxation of mammalian atrial muscle in late diastole may promote optimal filling of the ventricle.

Animals↗
PubMed1979

Nature of load dependence of relaxation in cardiac muscle.

Relaxation of spontaneously contracting single rat cardiac cells with an effective sarcoplasmic reticulum was shown to be sensitive to load, as previously described for intact mammalian ventricular cardiac muscle. Caffeine and tetanic stimulation could modify load-dependent relaxation in intact papillary muscle from cat or rat into a load-insensitive relaxation. Although such load dependence was demonstrated to be normally absent in frog ventricular cardiac muscle, in the present study it could also be made moderately manifest under specific conditions, e.g., high calcium, low sodium, or ouabain. The appearance of load dependence during relaxation in cardiac muscle thus emphasizes the presence of an effective sarcoplasmic reticulum.

Animals↗
PubMed1978

Relaxation of mammalian single cardiac cells after pretreatment with the detergent Brij-58.

1. The influence of load and activation on relaxation of heart muscle has been studied. 2. Cardiac cells devoid of functioning sarcolemma were isolated from rat and cat ventricular myocardium. Pretreatment with the detergent Brij-58 destroyed residual sarcoplasmic reticulum function. In order to analyse the mechanical properties of relaxation in these cells, a new miniature transducer was designed which could measure force by feedback sensing (resolution of 1 microgram). Contraction was induced by ionophoretically released calcium ions. Activation, sequestration of calcium and loading conditions could be controlled independently. 3. The time course of relaxation was shown to be governed by the amount of calcium released, and unlike intact preparations from rat or cat heart (but like those from frog), to be independent of load and of alterations in load. 4. We conclude that relaxation of the cardiac contractile system is determined basically by an activation-dependent mechanism, which is masked by load dependence in intact muscle preparations with a well developed calcium sequestering membraneous system.

Animals↗
PubMed1977

Force velocity relations of single cardiac muscle cells: calcium dependency.

Cellular cardiac preparations in which spontaneous activity was suppressed by EGTA buffering were isolated by microdissection. Uniform and reproducible contractions were induced by iontophoretically released calcium ions. No effects of a diffusional barrier to calcium ions between the micropipette and the contractile system were detected since the sensitivity of the mechanical performance for calcium was the same regardless of whether a constant amount of calcium ions was released from a single micropipette or from two micropipettes positioned at different sites along the longitudinal axis of the preparation. Force development, muscle length, and shortening velocity of eitherisometric or isotopic contractions were measured simultaneously. Initial length, and hence preload of the preparation were established by means of an electronic stop and any additional load was sensed as afterload. Mechanical performance was derived from force velocity relations and from the interrelationship between simultaneously measured force, length, and shortening velocity. From phase plane analysis of shortening velocity vs, instantaneous length during shortening and from load clamp experiments, the interrelationship between force, shortening, and velocity was shown to be independent of time during the major portion of shortening. Moreover, peak force, shortening, and velocity of shortening depended on the amount of calcium ions in the medium at low and high ionic strength.

Animals↗