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Biomedical subjects

M Stewart

Publications and source records attributed to M Stewart.

At least 379 records · Page 21Linked to original sources
PubMed1988

Platelet storage: changes in cytosolic Ca2+ actin polymerization and shape.

Platelets gradually lose their disc shape during storage. The authors studied simultaneous changes in platelet cytosolic Ca2+ (Cai) and the polymerization state of actin as related to the shape. Platelet concentrates were stored under blood bank conditions for up to 10 days. Aliquots were removed and analyzed as follows: platelet Cai and increments in Cai induced by adenosine diphosphate (ADP) were determined by fluorescence of fura-2-loaded cells; loss of disc shape was determined by differences in light scattering intensity induced by stirring; and the ratio of globular and total actin (G/T) of platelets in plasma was determined by a modification of the DNase inhibition assay. Globular actin was found to be 86 +/- 3% of total actin in freshly drawn platelets suspended in plasma. The following changes occurred during storage: G/T in platelet concentrates increased from 63 +/- 5 (day 0) to 74 +/- 2% in the first 24 hours then fell to 33 +/- 6% by day 10. The percent discoid platelets also increased from day 0 to day 1 then fell in the ensuing days. There was an initial drop in Cai from day 0 to day 1, after which Cai increased on days 3 and 6. Globular actin polymerization during storage closely correlated with the change in percent discs (r = 0.95). During 6 days of storage Cai was highly correlated with shape change (r = 0.97) and to a lesser extent (r = 0.87) with the ratio of globular actin. The authors conclude that actin polymerization, shape, and Ca2+ change in a related fashion during storage.

Actins↗
PubMed1987

Benign chylous ascites. A case report.

Although most cases of benign chylous ascites are a result of surgical trauma, inflammatory conditions and unknown causes still account for a significant proportion. A case of idiopathic chylous ascites is discussed to highlight the difficulties in diagnosis and management.

Adult↗
PubMed1987

A new crystal form of tropomyosin. Preliminary X-ray diffraction analysis.

A new crystalline form of tropomyosin has been produced that diffracts to about 4 A resolution. The crystals are grown at room temperature by slowly lowering the concentration of spermine. This polyamine apparently neutralizes the acidic amino acid side-chains of tropomyosin and allows close side-by-side packing of molecules. The space group is C2, with unit cell dimensions a = 259.7 A, b = 55.3 A, c = 135.6 A, and beta = 97.2 degrees. The tropomyosin molecules appear to be bonded head-to-tail to form straight filaments that run along the crystallographic (332) direction in an arrangement closely related to thin crystalline sheets previously described.

Crystallization↗
PubMed1987

A model to account for the elastic element in muscle crossbridges in terms of a bending myosin rod.

We advance a structural model to account for the rapid elastic element seen in mechanical transient experiments on vertebrate skeletal muscle (A.F. Huxley & Simmons 1971 Nature, Lond. 233, 533-538). In contrast to other crossbridge models, ours does not envisage a myosin rod made up of two rigid portions connected by a hinge, but rather a gradually bending rod portion connecting the heads to the thick filament shaft. We propose that, in relaxed muscle, the subfragment 2 (S2) portion of the myosin rod is bound to the thick filament shaft by ionic interactions analogous to those between the light meromyosin (LMM) portions of the rod that constitute the body of the shaft. These interactions probably involve the alternating zones of positive and negative charge seen in myosin rod amino acid sequences. As the crossbridge cycle that generates tension begins, we propose that part of S2 detaches from the thick filament shaft and bends to enable the myosin head to attach to actin. When tension develops in the crossbridge, the S2 is straightened and more of it becomes detached from the shaft so that the junction between S2 and the myosin heads moves 3-4 nm axially. As tension declines at the end of the crossbridge stroke, we propose that S2 rebinds to the thick filament shaft and that this provides the restoring force to return the junction of the heads and S2 to its original axial position. Thus this movement would have the characteristics of an elastic element; detailed calculations indicate that it would have properties similar to those observed experimentally. Furthermore, this model can account for the radial attractive force seen in rigor and in contracting muscle, the decrease in stiffness when interfilament spacing is increased in skinned muscle, and the increased rate of proteolysis observed at the S2-LMM junction in contracting muscle.

Animals↗
PubMed1987

Plunging ranula: a report of three cases and review of the literature.

Three cases of plunging ranula are reported and the literature reviewed. Extravasation of saliva from the sublingual gland due to trauma or obstruction of its ducts appears to be the most likely cause of plunging ranula. Available data suggest that the submandibular gland is usually not involved, although at the time of surgery it may be extremely difficult to exclude a submandibular origin of the cyst in the neck. Communication between the oral and cervical components of the plunging ranula probably occur via a hiatus in the mylohyoid muscle. Such communication passing directly into the submandibular compartment may simulate submandibular gland involvement. Since 1910, 139 procedures in 89 patients with plunging ranula have been reported in the English literature. The recurrence rate was 70 per cent after incision and drainage of the cyst, 53 per cent after marsupialization, 85 per cent after excision of the cyst in the neck and 2 per cent after excision of the sublingual gland via the cervical or intra-oral route. This review suggests that excision of the sublingual gland with intra-oral drainage of the cervical swelling appears to be the treatment of choice for the plunging ranula.

Adolescent↗
PubMed1987

Dyadic social-support for cardiac surgery patients--a Canadian approach.

Over the past 15 years there has been a substantial increase in the number of cardiac operations being performed. The role of the lay helper volunteer who has successfully recovered from cardiac surgery, offering support to individuals about to undergo similar surgery, is earning a legitimate place in cardiac rehabilitation. This 'living proof' model of support appears to have a significant buffering effect through increasing the cardiac patients' readiness for cardiac surgery and motivation for cardiac rehabilitation. Most literature focuses on individuals who have suffered a myocardial infarction rather than those who must undergo cardiac surgery. The focus of this article is lay volunteer dyadic social-support for open-heart surgery patients. The authors describe such a program operating in Halifax, Nova Scotia, designed to link volunteers who have successfully recovered from open-heart surgery with those individuals about to undergo similar surgery. Comparisons are also made with parallel support programs in Canada and the United States. Thus far, only crude measurements of the effectiveness of this particular social-support intervention are available. The dyadic social-support that volunteers offer cardiac surgery patients seems to be effective as evidenced by the information discussed in this paper.

Canada↗
PubMed1987

Crystalline tubes of myosin subfragment-2 showing the coiled-coil and molecular interaction geometry.

We have produced crystalline tubes of chicken breast myosin long subfragment-2 that show order to resolutions better than 2 nm. The tubes were formed from a thin sheet in which the myosin long subfragment-2 molecules were arranged on an approximately rectangular crystalline lattice with a = 14.1 +/- 0.2 nm and b = 3.9 +/- 0.1 nm in projection. Shadowing indicated that the tube wall was approximately 7 nm thick and that the sheets from which it was formed followed a right-handed helix. Superposition of the lattices from the top and bottom of the tube produced a moire pattern in negatively stained material, but images of single sheets were easily obtained by computer image processing. Although several molecules were superimposed perpendicular to the plane of the sheet, the modulation in density due to the coiled-coil envelope was clear, indicating that the coiled-coils in these molecules were in register (or staggered by an even number of quarter pitches). In projection the coiled-coil had an apparent pitch of 14.1 nm (the axial repeat of the unit cell), but the small number of molecules (probably four) superimposed perpendicular to the plane of the sheet meant that pitches within approximately 1 nm of this value could have shown a modulation. Therefore, a more precise determination of the coiled-coil pitch must await determination of the sheet's three-dimensional structure. The coiled-coils of adjacent molecules within the plane of the sheet were staggered by an odd number of quarter pitches. This arrangement was similar to that between paramyosin molecules in molluscan thick filaments and may have features in common with other coiled-coil protein assemblies, such as intermediate filaments. Each molecule in the crystal had two types of neighbor: one staggered by an odd number of quarter pitches and the other by an even number of quarter pitches, as has been proposed for the general packing of coiled-coils (Longley, W., 1975, J. Mol. Biol., 93:111-115). We propose a model for the detailed packing within the sheet whereby molecules are inclined slightly to the plane of the sheet so that its thickness is determined by the molecular length.

Animals↗
PubMed1987

Achalasia like disorder of the oesophagus in von Recklinghausen's neurofibromatosis.

The association of achalasia like disorder of the oesophagus with von Recklinghausen's neurofibromatosis to our knowledge not previously reported is described in a 56 year old man who also had bladder dysfunction. At necropsy the oesophageal myenteric plexus showed ganglion cell depletion with nerve fibre hyperplasia probably the result of Schwann cell hyperplasia. We suggest that the disturbances of oesophageal and bladder function were a consequence of involvement of the autonomic nervous system by neurofibromatosis.

Autonomic Nervous System Diseases↗
PubMed1987

A two-year follow-up of boys with aggressive conduct disorder.

53 boys with aggressive conduct disorder (ACD) and 36 with other psychiatric disorders were followed up after 2 years. Twenty-nine of the former (55%) still met the criteria for ACD; 24 did not. Persistence of the conduct disorder was predicted by the symptoms of hyperactivity and inattention. The data suggest that there are two types of ACD: one short-lived and quite benign, the other more likely to persist and more serious.

Adolescent↗
PubMed1987

Flow properties of modified packed red cells.

We investigated free gravitational blood flow of modified packed red cells. Variables affecting free flow included final haematocrit, duration of blood storage at 4-6 degrees C and the centrifugal force required in preparation of this blood component. Irrespective of the duration of storage, free blood flow of modified packed red cells was not different from whole blood, provided the haematocrit did not exceed 0.63.

Blood Flow Velocity↗
PubMed1987

Henoch-Schönlein purpura: problems in surgical diagnosis and management.

The clinico-pathological features of 133 consecutive cases of Henoch-Schönlein purpura are presented, with emphasis on the gastrointestinal manifestations. The potential pitfalls of contrast radiography are underlined with respect to management of intussusception and a plea is made to re-establish clinical assessment of the abdomen as the prime indicator in deciding to undertake laparotomy.

Abdomen↗
PubMed1987

Physiological basis of motor effects of a transient stimulus to cerebral cortex.

This contribution includes a selective review of previously published material, findings from some new experiments, and discussion of some relationships between animal and recent human data. The major questions are: What descends from the cerebral cortex after a brief surface stimulus? What explains the various components of the corticofugal discharge? What are the motor consequences of the corticofugal discharge, and what are the effects of lesions on both? The focus is on the corticospinal system, which through its monosynaptic connection with alpha motoneurons of distal muscles accounts for the short latency movements after a transient cortical stimulus. The pyramidal and lateral corticospinal tract response in monkey or cat to a surface stimulus applied to area 4 is a direct (D) wave conducted in fast axons followed by several indirect (I) waves with a period of greater than 1 ms. Although computer summing reveals, at increasing amplitudes, D and I waves in recordings from nuchal skin, vertebra, and surface of the spinal cord, "killed end" recording is essential to reveal the true extent of I relative to D waves. The D wave might result from excitation of: the initial segment (IS), i.e., the classical spike trigger zone; the first or deeper nodes in white matter; or arborizations of the axon collaterals in gray matter. Under different circumstances, each of these modes of excitation can be effective. Thus, with threshold stimulation through separated bipolar electrodes, intracellular recording from pyramidal tract (PT) and uninvaded motor cortical neurons shows that D activation usually occurs when the membrane potential immediately before the stimulus is relatively depolarized, implying excitation of the IS region, i.e., close to the site of synaptic transfer. A monopolar surface (+) stimulus at the appropriate focus usually generates a D wave at weaker intensity than does a surface (-) stimulus. However, if a little above threshold, stimuli of either polarity generate both D and I waves, but the ratio of D:I amplitude is usually greater with surface (+) stimulation. A theoretical estimate of the depth of excitation by a surface (+) stimulus was consistent with threshold excitation occurring at the first node. Slow PT neurons are excited by surface stimulation, but trivially contribute to population PT or corticospinal recordings. Intracellular recording from PT neurons identifies a monosynaptic excitatory postsynaptic potential as the cause of the first I wave, the period between successive I waves reflecting single delays for synaptic discharge.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Arrangement of myosin heads in relaxed thick filaments from frog skeletal muscle.

The distribution of myosin heads on the surface of frog skeletal muscle thick filaments has been determined by computer processing of electron micrographs of isolated filaments stained with tannic acid and uranyl acetate. The heads are arranged in three strands but not in a strictly helical manner and so the structure has cylindrical symmetry. This accounts for the "forbidden" meridional reflections seen in diffraction patterns. Each layer-line therefore represents the sum of terms of Bessel orders 0, +/- 3, +/- 6, +/- 9 and so on. These terms interact so that, unlike a helical object without terms from overlapping Bessel orders, as the azimuth is changed, the amplitude on a layer-line at a particular radius varies substantially and its phase does not alter linearly. Consequently, a three-dimensional reconstruction cannot be produced from a single view. We have therefore used tilt series of three individual filaments to decompose the data on layer-lines 0 to 6 into terms of Bessel orders up to +/- 9 using a least-squares procedure. These data had a least-squares residual of 0.32 and enabled a three-dimensional reconstruction to be obtained at a nominal resolution of 6 nm. This showed, at a radius of about 10 nm, three strands of projecting morphological units with three units spaced along each strand every 42.9 nm axially. We have identified these units with pairs of myosin heads. Successive units along a strand are perturbed axially, azimuthally and radially from the positions expected if the structure was perfectly helical. This may simply be a consequence of steric restrictions in packing the heads on the thick filament surface, but could also reflect an underlying non-helical arrangement of myosin tails, which would be consistent with the thick filament shaft being constructed from three subfilaments in which the tails were arranged regularly. There was also material at a radius of about 6 nm spaced 42.9 nm axially, which we tentatively identified with accessory proteins. The filament shaft had a pronounced pattern of axial staining.

Animals↗