Local Contraction Research Articles

Long-lasting exocytosis and massive structural reorganisation in the egg periphery during cortical reaction inPlatynereis dumerilii(Annelida, Polychaeta)

The course of the cortical reaction in the Platynereis dumerilii egg is described from live observation and from sectioned fixed material and is found to differ in several aspects from the course of cortical reactions in better-known systems. Cortical granules are unusually numerous. They are discharged by exocytosis during a period of about 25 min following fertilisation (18 degrees C). Most of the surplus membrane material brought to the egg surface by exocytosis is set free into the perivitelline space. Swelling of egg jelly precursor secreted by cortical granule exocytosis may be causal for the detachment of the vitelline envelope from the egg cell surface which, however, remains attached punctately to the vitelline envelope by about 30,000 microvilli. Under the strain of the distending vitelline envelope, the bases of the microvilli move and line up, pulling the cell surface into a network of ridges. The grooves in between the ridges are the sites of exocytoses. Cytochalasin B, generally destabilising actin filaments, induces rupture of the microvilli and exaggerated distension of the vitelline envelope during the cortical reaction. In a final phase of the cortical reaction the vitelline envelope wrinkles and falls back onto the egg cell surface, the microvilli shorten and the egg cell transiently becomes deformed by local contractions. The cortical reaction in the nereid egg is discussed as a process of distortion and reorganisation of the egg cortex and plasmalemma. The abundance of cortical granules accommodating egg jelly precursor in the Platynereis oocyte is attributed to the mode of so-called diffuse oogenesis characteristic of nereids, i.e. of differentiation of oocytes freely suspended in the coelomic fluid. In nereids, egg jelly therefore forms after fertilisation as opposed to ovulation.

Local behavior in the cubic-rhombohedral phase transition for Fe 3+ ions in LaAlO 3 crystal

In this Letter, by introducing a factor f to denote the contraction of AlO 6 octahedra along the trigonal axis in the structural phase transition from cubic to rhombohedral symmetry, a simple and uniform expression for calculating the zero-field splitting D in the rhombohedral phase from the spin-lattice coupling coefficient G 44 in the cubic phase for paramagnetic ions in the perovskite structure is established. Based on this, the local behavior for a Fe 3+ ion in LaAlO 3 crystal at the transition is studied from the EPR spectrum. It is found that, to reach a good fit between theory and experiment, the local contraction factor f in the vicinity of the Fe 3+ ion should be about five times that of the host ion.

Importance of supravitality in forensic medicine

Based on physiological investigations on latency period, survival period and resuscitation period under complete temporary ischemia, supravitality can be defined as even longer survival period of tissues (compared to the resuscitation period) after complete irreversible ischemia. Supravitality is mostly defined by functional parameters (sensitivity to excitation). Parameters of supravital metabolism (substrates and metabolites of anaerobic glycolysis) as a basis for supravital reactions (sensitivity to excitation) are discussed. Particular supravital reaction patterns in comparison to physiological conditions are mentioned (Cannon — Rosenbluth's law of denervation, supersensitivity to pharmacological excitation, local contraction instead of propagated excitation). Lastly, morphological alterations which can be induced during the early supravital period (latency period, survival period) as well as their destination from local vital reactions will be briefly mentioned.

Long descending excitatory nervous pathways do not appear to modulate local reflex contractions during peristalsis in the isolated guinea-pig ileum

Long descending excitatory nervous pathways do not appear to modulate local reflex contractions during peristalsis in the isolated guinea-pig ileum

An in vitro model of fibroblast activity and adhesion formation during flexor tendon healing

We studied fibroblast activity during tendon healing with an in vitro tendon culture model. Tendons were embedded in a translucent collagen gel matrix whose porous nature permitted free nutrient diffusion, fibroblast migration out of the tendon, and microphotographic documentation of fibroblast activity. Experiments were performed using one or more tendons cultured in the same collagen gel. We identified three zones of fibroblast activity in the gel. Zone I was an area of randomly dispersed cells directly adjacent to the tendon where collagen synthesis and remodeling were probably taking place. In zone II, spindle-shaped fibroblasts were aligned pointing away from the cut tendon end forming a sunburst-like aggregate of cells. Zone II fibroblasts were responsible for formation of migration trails by exerting a mechanical force on the collagen matrix, which was evident as a local gel contraction. Zone III was the leading edge of the sunburst populated by the fastest moving fibroblasts, which responded to guidance by other cut tendon ends. We speculate that the collagen gel used in the culture system may help maintain a chemotactic concentration gradient that allows fibroblasts to locate other distal cut tendon surfaces also embedded in the collagen gel.

Furrowing surface contraction wave coincident with primary neural induction in amphibian embryos.

We predicted, and have now observed, a surface contraction wave in axolotl (Ambystoma mexicanum) embryos that appears to coincide temporally and spatially with primary neural induction and homoiogenetic induction, and with involution of the chordomesoderm. The wave starts from a focus anterior to the dorsal lip of the blastopore and spreads as an ellipse, until part of it encounters the rim of the blastopore and vanishes there. The remaining arc then continues over the dorsal hemisphere until it reforms an ellipse that decreases in size. About 9 to 12 hours after it begins, the wave vanishes at a focus diametrically opposite its point of origin. The wave involves both local contraction and furrowing in the monolayer ectoderm. To a good approximation, the hemispherical portion of the ectoderm traversed by the wave becomes neuroepithelium, while the ectoderm not traversed by the wave becomes epidermis. The wave might provide a mechanism to determine the time and location at which neuroepithelial differentiation occurs.

Pyloric motility and liquid gastric emptying during barostatic control of gastric pressure in pigs.

1. In conscious pigs, intragastric pressure was controlled by a water barostat such that the gastroduodenal pressure gradient was always positive with the barostat set above 15 cm. In six pigs pyloric motor function was removed by prior pylorectomy. 2. In pylorus-intact animals, isolated pyloric pressure waves (IPPWs) occurred at a median of 2.9 min-1 during duodenal dextrose infusion with the barostat set at or above a threshold of 15 cm. Increases of intragastric pressure above this threshold had no additional effect upon rates of IPPWs. Below this threshold, with identical duodenal dextrose infusion, IPPWs occurred infrequently (0.5 min-1). In pylorus-excised animals virtually no IPPWs were seen. 3. In both pylorus-intact and -excised animals, the rate of antral pressure waves (APWs) was dependent upon intragastric pressure during duodenal infusion of both saline and dextrose. No threshold for stimulation was seen. Duodenal dextrose infusion inhibited APWs in pylorus-intact animals only. 4. With a positive gastroduodenal pressure gradient, gastric emptying was more rapid in pylorus-excised animals than pylorus-intact animals during duodenal dextrose infusion. In contrast, gastric emptying rates were not different between pylorus-intact and -excised animals during saline infusion. 5. These findings suggest an all-or-none-type stimulation of localized pyloric contractions by distension of the stomach beyond a threshold, in synergism with stimulation by nutrients within the upper small bowel. In contrast, stimulation of antral motility is in proportion to distension of the stomach. The pylorus, by way of localized pyloric contractions, is an effective resistor to transpyloric flow in the face of a positive gastroduodenal pressure gradient.

Local contractions induce an ascending contraction mediated by 5-HT 3 receptors in the canine small intestine

Local contractions induce an ascending contraction mediated by 5-HT 3 receptors in the canine small intestine

The dynamics of local tissue damage induced by Bothrops asper snake venom and myotoxin II on the mouse cremaster muscle: An intravital and electron microscopic study

The acute tissue damaging effects of Bothrops asper snake venom and a myotoxic Lys-49 phospholipase A 2 (myotoxin II) on the mouse cremaster muscle were studied by intravital and electron microscopy. Both venom and myotoxin induced local contractions of the muscle fibres within 10–60 sec after exposure, which disappeared after 1–2 min. This observation is consistent with the hypothesis that Bothrops myotoxins act initially at the sarcolemma by affecting its permeability and allowing an influx of calcium. The venom also induced an early but transient vasoconstriction of arterioles. The development of edema was monitored using i.v. FITC-dextran as a marker. Plasma leakage started after about 2 min of exposure to venom or myotoxin, was extensive by 4–5 min, and originated from small venules and their adjoining capillary segments. The venom induced formation of thrombi and emboli in venules, but not in arterioles. Haemorrhage appeared after 4–6 min of exposure, the bleedings always originating from capillaries and small venules. The microbleedings were explosive, appearing as rapid bursts of erythrocytes into the extravascular space, and suggesting a per rhexis type of haemorrhage. This was confirmed by electron microscopy evaluation of the same microvessels observed intravitally, which showed erythrocyte extravasation through gaps in damaged endothelial cells. Other phenomena in the microcirculation included blood-flow disturbances, crenation and sphering of erythrocytes, and stasis with dense packing of cells in capillary networks. Muscle necrosis, caused by either venom or myotoxin, started 3–4 min after application. The first sign of damage in the fibres was the development of a narrow, transverse band with local loss of striation. This was followed by slow retraction of myofibrils until there was a complete transverse rupture of the fibre. This process was often repeated along the same fibre, leaving a row of fragments separated by spaces apparently devoid of myofibrillar material. The results confirm the rapid tissue damaging effects of B. asper venom, implying that potentially useful blocking agents must be administered early and have the ability to diffuse rapidly into the tissues.

Effects of cardiac contraction and cavity pressure on myocardial blood flow

Regional impairment of cardiac contraction uncouples force generation from left ventricular pressure (LVP) and may alter the determinants of the phasic pattern and transmural distribution of coronary flow. In anesthetized, open-chest dogs with maximal coronary vasodilation, we studied the effects of abolishing local contraction and changing cavity pressure on phasic myocardial inflow and net transmural flow in a region of left ventricular free wall. With contraction present, the normalized amplitude of distal phasic coronary velocity (NAmp) was not significantly different at normal vs. low LVP (1.00 vs. 0.92 +/- 0.09, respectively, intracoronary lidocaine, however, NAmp varied with LVP (1.62 +/- 0.25 at normal LVP, 0.85 +/- 0.22 at low LVP, P < 0.0001). With contraction present, inner-to-outer flow ratio was not consistently different at normal vs. low LVP (0.47 +/- 0.15 vs. 0.64 +/- 0.28, respectively, P = NS) but was consistently higher at low than at normal LVP with contraction absent (1.01 +/- 0.30 vs. 1.84 +/- 0.38, respectively, P < 0.0001). During uniform global function, contraction is the main determinant of phasic amplitude and transmural distribution of myocardial flow. When regional contraction is abolished, allowing passive deformation of the wall during systole, LVP assumes a powerful role.

Organization of antral, pyloric and duodenal motility in patients with gastroparesis

AbstractThe motor mechanisms associated with delayed gastric emptying are poorly understood, and the contribution of abnormal patterns of gastroduodenal motility to gastroparesis is unknown. Limited data suggest an increased frequency of localized pyloric contractions contributes to delayed gastric emptying. Antropyloroduodenal pressures and gastric emptying of 99mTc chicken liver/ground beef were recorded simultaneously for 60 min in 16 patients with gastroparesis and 26 healthy subjects, using a sleeve/sidehole manometric assembly and a scintigraphic technique. Manometric recordings were analysed for localized pyloric contractions (isolated pyloric pressure waves), basal pyloric pressure (tone), antral and duodenal pressure waves and the number of associated antropyloroduodenal contractions ≥6 cm in length. There was no significant difference in median pyloric tone (1.1 (interquartile range 0.3–2.1) vs 0.5 (0–1.8)mmHg), number of isolated pyloric pressure waves (15 (4.5–25) vs 25 (12–37)) or antral pressure waves (47 (16–62) vs 46 (17–76) between the patients with gastroparesis and the healthy controls. The number of duodenal pressure waves was significantly less in the gastroparetics (54 (41–80) vs 102 (63–116), P &lt; 0.05) as was the number of antropyloroduodenal pressure waves ≥6 cm (5 (0.5–6) vs 12.5 (4–24), P &lt; 0.05). There was no difference in the lag time for solid gastric emptying, but there was a reduction in the amount emptied after 60 min (1 (0–10) vs 10 (0–14)%, P &lt; 0.01). These results suggest that abnormal patterns of antropyloroduodenal contractions contribute to slow gastric emptying in patients with gastroparesis. Localized pyloric contractions are not a major pathogenetic mechanism.

Transmitter-mediated local contracture of the endplate region of the focally innervated mouse diaphragm treated with anticholinesterase.

1. Local contraction of the endplate region in response to nerve stimulation was studied in isolated mouse diaphragms. In normal preparations, muscle contractions involved the whole length of the muscle fibre with rise and decay times in the order of tens of ms whether evoked with a single or train of pulses. 2. When acetylcholinesterase was inhibited with neostigmine, tetanic stimulation produced a twitch-like phasic contraction and a delayed tonic contracture. A brief train of pulse (10 ms, 300 Hz) was enough to trigger a full size tonic contracture which reached an amplitude about one tenth that of control tetanus and had a duration of about 4 s. 3. Tetanic stimulation evoked a non-propagating prolonged depolarization at the endplate region lasting for about 1 s following a few muscle action potentials. 4. mu-Conotoxin, a specific inhibitor of muscle Na+ channel, selectively abolished the phasic contraction and the muscle action potentials leaving the tonic contracture and the prolonged depolarization unaffected. 5. Both the tonic contracture and the prolonged depolarization were highly sensitive to blockade by tubocurarine (IC50 0.05-0.1 microM) and vesamicol (1 microM, an inhibitor of packaging acetylcholine into synaptic vesicles), were attenuated by increasing Ca2+ concentration and were prolonged by decreasing Ca2+. 6. The results suggest that prolonged activation of endplate nicotinic receptors by endogenously released transmitter can produce substantial contractions of the endplate region when acetylcholinesterase are inhibited. The source of Ca2+ for the contraction seems to come mainly from intracellular stores.

Investigation of hot-fluid cavitating flow through an obstacle in a pipeline

The results of investigating hot-fluid cavitating flow in a pipe with a local contraction are presented for a broad temperature interval (water from cold to near-boiling) and various cavitation regimes — from the initial (bubble) to the supercavitation regime. Experimental relations for the amplitudes of the fluctuations and the fundamental frequencies are presented for a Venturi tube with various diffusers and for diaphragms of various dimensions. A flow model which takes into account the fluctuations of the vapor pressure in the cavity and, moreover liquid-cavity mass transfer effects is presented. It is shown that for a given flow geometry there is a limiting Jakob number below which the self-oscillating regime is impossible at any cavitation numbers.

Beta-adrenergic blockade improves uniformity of local contraction in the anterior wall of feline left ventricles.

Uniformity of myocardial contraction has been put forward as an important regulatory mechanism of myocardial contraction, and we have previously demonstrated reduced uniformity of local myocardial contraction in the midwall of left ventricles during preload reduction combined with increased inotropy. The aim of the present study was to explore the isolated inotropic influence on uniformity of contraction, keeping loading conditions constant. Segment performance was measured by implanted piezo-electric crystals in ten open-chest, anaesthetized cats. One crystal pair, circumferential segment, aligned with midwall and epicardial fibres, whereas another perpendicular segment, longitudinal, ran close to endocardial fibre direction. Maximal systolic shortening of longitudinal segments remained unchanged following inotropic interventions, isoprenaline and timolol, whereas circumferential segments revealed reduced performance with timolol (8.4 +/- 1.0% compared with 14.0 +/- 1.3% during control; P < 0.001). In the control state the longitudinal-to-circumferential ratio (LONG/CIRC) a quantitative measure of uniformity, was 0.32 +/- 0.08. No change in uniformity occurred during isoprenaline infusion (0.32 +/- 0.11) but during beta-adrenergic blockade with timolol a clearly higher LONG/CIRC ratio was observed (0.56 +/- 0.06, P < 0.005). Myocardial tissue blood flow measurement by radioactive microspheres showed a shift in transmural distribution with interventions so that subepicardial blood flow was markedly reduced during beta-adrenergic blockade. The direction of subepicardial fibres approximates our circumferential segments. Thus, there may well exist a relationship between segmental shortening and perfusion. In conclusion, circumferential segments were most influenced by changes in inotropy in contrast to previous observations where pronounced changes in longitudinal segments with loading occur. Furthermore, this study demonstrates that reduced inotropy with timolol helped uniform local contraction as estimated by the increased LONG/CIRC ratio, a transition that could improve contraction efficacy.

New concepts in relation to urge and detrusor activity

Investigations of micromotion characteristics of bladder wall strips and pressure wave phenomena in total bladders in vitro and in vivo indicate that micromotion phenomena occur in the bladder wall. Local contractions can occur without an increase in tension or pressure, because other parts are in antiphase. Local contractions stretch surrounding tissues, which can stimulate fast stretch receptors. Synchronisation of these micromotion phenomena appears to be possible. Hence, above threshold levels urge can theoretically occur, even in the absence of a pressure increase. This hypothesis could explain the weak relation between urge and pressure. The distinction between motor and sensory urge could be artifactual based on a misunderstanding of fundamental bladder wall processes.

Ecology of the rufous hare-wallaby, Lagorchestes hirsutus Gould (Marsupialia : Macropodidae) in the Tanami Desert, Northern Territory.I Patterns of habitat use.

A 2-year study was conducted to investigate two aspects of the local distribution of the rufous harewallaby, Lagorchestes hirsutus, in a region of the Tanami Desert. These were: (a) patterns of habitat use in response to changing environmental conditions and (b) environmental parameters influencing 'local' choice of habitat. Counts of faecal pellets and tracks were used to obtain indices of hare-wallaby activity within occupied sites and to gain an insight into the movements by individuals. Local choice of habitat was analysed by assessment of numerous habitat features at occupied and unoccupied sites in the region. Previous surveys over the greater part of the study area provide evidence of a significant local decline and local contraction of range by L. hirsutus during recent times. Hare-wallabies showed seasonal trends in the relative use of different vegetation systems in response to the relative availability of food items within each habitat. The home ranges of hare-wallabies consisted of two distinct areas of activity: a large sparsely used area within the dense Triodia pungens vegetation and a small concentrated feeding area within the neighbouring caliche system. Hare-wallabies were dependent upon a specialised form of spinifex habitat. Patchiness, hummock size, food diversity and the degree of floral senescence affected suitability for hare-wallabies. Within the Tanami Desert site, suitable combinations of these characters were associated with tight mosaics of different regenerative stages after fire. Fire is therefore clearly implicated as an important force in creating a greater diversity of feeding and sheltering habitats for the hare-wallabies in the otherwise uniform spinifex sandplains. There is an obvious role for the application of controlled burns as a means of managing habitats to favour L. hirsutus in the Tanami Desert.

Stimulation of pyloric contractions by intraduodenal triglyceride is persistent and sensitive to atropine.

Intraduodenal lipid infusion stimulates phasic and tonic pyloric contractions and suppresses antral contractions. This study determined: (i) whether this response is sustained over 90 min; and (ii) the role of muscarinic mediation of this response. Antropyloroduodenal motility was recorded in 17 healthy volunteers with a sleeve/sidehole manometric assembly. Subjects received either a 90 min intraduodenal infusion of saline or triglyceride (20% Intralipid) at a rate of 1 mL/min; 30 min after the start of this infusion, the eight subjects who received triglyceride were given intravenous atropine 15 micrograms/kg over 30 s, followed by a maintenance infusion of 4 micrograms/kg/h until the study was completed. Intraduodenal triglyceride infusion stimulated isolated pyloric pressure waves consistently, producing a median rate of 2.4 per min after 30 min of triglyceride infusion, compared with a median rate of 0 per min pre-infusion. In intravenous saline studies, there was a reduction (P < 0.05) in the median rate of isolated pyloric pressure waves to 1.3 per min at 90 min, when compared with pyloric pressure waves at 30 min. Atropine reduced isolated pyloric pressure waves to a median rate of 0 per min, significantly different from preatropine (P < 0.01) and from intravenous saline studies (P < 0.0001). These results indicate that the phasic pyloric response to intraduodenal lipid persists during 90 min stimulation, albeit with significant attenuation. In humans, muscarinic cholinergic blockade prevents the occurrence of triglyceride stimulated localized pyloric contractions.

Effects of exercise on insulin sensitivity in humans.

Physical exercise is promoted as one of the primary therapeutic strategies available to increase insulin sensitivity in individuals deemed at risk from insulin resistance and its attendant hyperinsulinism. Subjects with non-insulin-dependent diabetes mellitus (NIDDM) and impaired glucose tolerance (IGT) represent the major clinical population in which physical training is promoted as a treatment modality to improve insulin sensitivity. This manuscript reviews both the acute effects of muscular contractions and the effects of physical training on insulin sensitivity in NIDDM and insulin-dependent diabetic (IDDM) human subjects. Additionally, the effects of localized (regional) muscular contractions on insulin-mediated glucose disposal in previously exercised and nonexercised muscle groups will be discussed briefly.

Room-temperature tensile deformation of polysynthetically twinned (PST) crystals of TiAl

Tensile deformation behavior of polysynthetically twinned (PST) crystals of TiAl with a nearly stoichiometric composition was investigated as a function of the angle ø between the lamellar boundaries and tensile axis at room temperature. Tensile elongation to fracture strongly depends on the angle ø but its dependence on the angle ø is not symmetrical with respect to ø = 45°. A tensile elongation as large as 20%, which is far larger than any other reported values on TiAl-based compounds, has been obtained for ø = 31°. The yield stress also strongly depends on the angle ø but any particularly significant tension-compression asymmetry in yield stress has not been observed. Fracture has been found to occur in a brittle manner without showing any local contraction even after deformation to more than 10%. When the tensile axis is perpendicular or inclined to the lamellar boundaries, fracture occurs in a cleavage-like mode with a habit plane parallel to the lamellar boundaries while fracture occurs in a zigzag across the lamellar boundaries when the tensile axis is parallel to the lamellar boundaries.

Intravenous erythromycin overcomes small intestinal feedback on antral, pyloric, and duodenal motility

The retardation of gastric emptying caused by intraduodenal lipid is associated with suppression of antral contractions and stimulation of localized pyloric contractions. Similar patterns of motility have been described in patients with gastroparesis. The effect of erythromycin on the antropyloroduodenal motor responses to intraduodenal lipid was investigated. In 17 volunteers an intraduodenal lipid infusion (10% Intralipid) was given at 1 mL/min for 50 minutes. Either erythromycin (3 mg/kg) or saline was administered IV for 15 minutes, beginning 20 minutes after the start of the intraduodenal lipid infusion. Antral, pyloric, and duodenal motility were measured with a sleeve/sidehole manometric assembly. Intraduodenal lipid stimulated localized pyloric contractions. Erythromycin suppressed localized phasic (P < 0.003) and tonic (P < 0.002) pyloric pressure waves and stimulated antral (P < 0.003) and duodenal pressure waves (P < 0.02). After erythromycin antral pressure waves were usually of high amplitude (>50 mm Hg) and often associated with duodenal pressure waves. It was concluded that erythromycin overcomes the effects of intraduodenal lipid on antral, pyloric, and duodenal motility. These effects probably contribute to the gastrokinetic properties of erythromycin.