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Biomedical subjects

J M Clark

Publications and source records attributed to J M Clark.

At least 163 records · Page 9Linked to original sources
PubMed1990

Cuticular lipid differences between the malaria vector and non-vector forms of the Anopheles maculatus complex.

Two chromosomal forms (E and F) of the Anopheles maculatus Theobald complex were distinguished by gas-liquid chromatographic (GC) analysis of cuticular lipids in association with a multivariate principal component analysis. The GC chromatogram obtained from n-hexane extracts of individual specimens showed no consistent qualitative differences in normalized peak areas between forms. Of the seventeen consistent peaks, five were found to be quantitatively different between forms at a high (99.5-99.95%) level of statistical confidence. Relative ratios of these five quantitatively different GC peaks were used as criteria to distinguish single specimens as either form E or form F. Chemical structures of the five GC peaks were assigned by both electron impact and chemical ionization gas chromatography/mass spectrometry analysis. The first three peaks, which were always doublets, were partially resolved saturated and mono-unsaturated free fatty acids; the other two peaks were n-alkanes. Principal component analysis substantiated that the vector form E has very similar cuticular lipid profiles and is well separated from the non-vector form F.

Animals↗
PubMed1990

The structure of the human subchondral plate.

To study the anatomy of subarticular bone and cartilage, fresh specimens of cartilage on bone from the human shoulder, hip and knee were treated with bleach or papain, or were fixed and decalcified. All were compared using scanning electron microscopy. Papain digestion selectively removed cartilage to the tidemark. The tidemark contour was highly variable; irregularities were indirectly related to degenerative lesions and were most prominent in peripheral non-weight-bearing areas of joints with central fibrillation. Decalcification exposed the interface between the bone and calcified cartilage. Collagen fibrils in articular cartilage did not interdigitate with those of bone. The subchondral bone was appositional, avascular, smooth and very thin in most areas of human joints. Perforations through subchondral bone or calcified cartilage were rare. Bleach maceration destroyed important details.

Adolescent↗
PubMed1990

The structure of vascular channels in the subchondral plate.

Human, rabbit and canine articular cartilage was prepared for SEM by fixation in isosmolal glutaraldehyde and freeze-fracture following dehydration. These techniques produced clear images of the bone, marrow and vessels in the subchondral region. Generally, cavities larger than 40 microns contained elements typical of marrow. Capillaries ran through the bone in cylindrical channels 20-40 microns wide. These channels were surrounded by concentric lamellae of bone and were in all respects Haversian canals within osteons. A minority of these channels opened into the calcified articular cartilage and there were preceded by cells which appeared to be cutting into the cartilage. Most vascular channels, however, were separated from the cartilage by a layer of bone. We conclude that the vessels within subchondral bone are present primarily to supply the bone through a network of mature osteons.

Adolescent↗
PubMed1990

The organisation of collagen fibrils in the superficial zones of articular cartilage.

The origin and structure of collagen fibres in the surface of articular cartilage were studied using SEM. Cryofracture was used to create orthogonal fracture surfaces in three planes. Fibres which originated in the radial zone could be traced into the surface where they flattened and overlapped in a common direction. Thick fibres from the periosteum ran into the surface as well, but apparently ended there and did not enter the radial zone. The tangential fibres were covered by a dense, separate layer of small fibrils. The fundamental aspects of the model proposed by Benninghoff are supported by these findings.

Adult↗
PubMed1990

Translation of the humeral head on the glenoid with passive glenohumeral motion.

We have demonstrated that certain passive motions of the glenohumeral joint are reproducibly accompanied by translation of the head of the humerus on the glenoid. We investigated the relationship of these translations to the position of the glenohumeral joint and to applied torques and forces in seven isolated glenohumeral joints from fresh cadavera, using a six-degrees-of-freedom position sensor and a six-axis force and torque transducer. Reproducible and significant translation occurred in an anterior direction with glenohumeral flexion and in a posterior direction with extension. We also observed translation with cross-body movement. The translation occurring with flexion was obligate in that it could not be prevented by the application of an oppositely directed force of thirty to forty newtons. Operative tightening of the posterior portion of the capsule increased the anterior translation on flexion and cross-body movement and caused it to occur earlier in the arc of motion compared with the intact glenohumeral joint. Operative tightening of the posterior part of the capsule also resulted in significant superior translation with flexion of the glenohumeral joint.

Aged↗
PubMed1989

Role of ion channels and intraterminal calcium homeostasis in the action of deltamethrin at presynaptic nerve terminals.

Using a continuous perfusion system, synaptosomes prepared from rat brain released [3H]norepinephrine in a Ca2+-dependent manner when pulse depolarized by briefly elevating external potassium concentrations. Tetrodotoxin (10(-7) M), a sodium channel blocker, inhibited 48% of this pulsed release, and D595 (10(-5) M), a phenethylamine-type calcium channel blocker, inhibited 21%. In combination, these two specific ion channel antagonists appear to function independently of each other in an additive fashion. Addition of deltamethrin to this preparation resulted in an enhanced release of [3H]norepinephrine which occurred in a biphasic fashion. At 10(-7) M, deltamethrin produced a 42% enhancement in the first or initial peak of [3H]norepinephrine release and a 100% enhancement in the second or tailing peak. Addition of deltamethrin to tetrodotoxin-pretreated synaptosomes resulted in a net 37% enhancement of the initial peak release and a net increase of 277% in the tailing peak. Addition of deltamethrin to D595-pretreated synaptosomes produced no significant effect on enhanced [3H]norepinephrine release from either peak. Since tetrodotoxin is a specific sodium channel blocker, deltamethrin may be enhancing [3H]norepinephrine release by increasing the uptake of Ca2 via other voltage-gated channels (e.g. calcium) or exchange mechanisms in addition to its action at voltage-gated sodium channels. To determine whether deltamethrin may also have an effect on intraterminal Ca2+ homeostasis, external Ca2+ was replaced with Ba2+ and synaptosomes were depolarized with pentylenetetrazole (PTZ). At 10(-5) M, deltamethrin produced a 66% increase in neurotransmitter release over that produced by PTZ alone. An estimated EC50 value of deltamethrin for PTZ-induced release was calculated to be 2.4 x 10(-10) M.

Animals↗
PubMed1989

Template length, sequence context, and 3'-5' exonuclease activity modulate replicative bypass of thymine glycol lesions in vitro.

cis-Thymine glycol, a product of ionizing radiation damage to DNA, has been introduced quantitatively at a single site into oligonucleotide templates. The ability of DNA polymerases to replicate templates containing thymine glycol was studied by a primer extension assay, and three factors that influence replicative bypass of this lesion in vitro have been identified. These factors include template length, sequence context, and 3'-5' exonuclease activity. Synthesis by the large fragment of DNA polymerase I (Klenow fragment) terminates quantitatively opposite thymine glycol when the template strand extends only two nucleotides beyond the lesion. Significant bypass is observed when the length of the template beyond the lesion is increased to six nucleotides. On the longer templates, the frequency of bypass of the Klenow fragment depends upon the identity of the base immediately 5' to thymine glycol. The extent of bypass is greatest with cytosine and least with adenine at this position. Bypass of thymine glycol lesions by DNA polymerase alpha 2 from HeLa cells shows a qualitatively similar dependence upon local sequence context. In contrast, synthesis by T4 DNA polymerase is quantitatively blocked opposite the lesion regardless of template length or DNA sequence context. Synthesis by a mutant Klenow fragment that is deficient in 3'-5' exonuclease activity, or by AMV reverse transcriptase, results in a significant increase in the frequency of bypass. Thus, increased nucleotide turnover at, or beyond, the site of the lesion is likely to contribute significantly to the arrest of synthesis provoked by cis-thymine glycol in vitro.

Base Sequence↗
PubMed1989

Deltamethrin causes changes in protein phosphorylation activities associated with post-depolarization events in the synaptosomes from the optic lobe of squid, Loligo pealei.

1. Deltamethrin causes a significant change in protein phosphorylation activities which follow depolarization. 2. The most significant change caused by deltamethrin was the prolonged elevation of the level of phosphorylation on a number of key synaptic proteins beyond the normal time of their recovery to the dephosphorylated state. 3. The best marker proteins reacting to deltamethrin in this manner were calcium-calmodulin dependent protein kinase and synapsin I.

Animals↗
PubMed1989

Referential processing: reciprocity and correlates of naming and imaging.

To shed light on the referential processes that underlie mental translation between representations of objects and words, we studied the reciprocity and determinants of naming and imaging reaction times (RT). Ninety-six subjects pressed a key when they had covertly named 248 pictures or imaged to their names. Mean naming and imagery RTs for each item were correlated with one another, and with properties of names, images, and their interconnections suggested by prior research and dual coding theory. Imagery RTs correlated .56 (df = 246) with manual naming RTs and .58 with voicekey naming RTs from prior studies. A factor analysis of the RTs and of 31 item characteristics revealed 7 dimensions. Imagery and naming RTs loaded on a common referential factor that included variables related to both directions of processing (e.g., missing names and missing images). Naming RTs also loaded on a nonverbal-to-verbal factor that included such variables as number of different names, whereas imagery RTs loaded on a verbal-to-nonverbal factor that included such variables as rated consistency of imagery. The other factors were verbal familiarity, verbal complexity, nonverbal familiarity, and nonverbal complexity. The findings confirm the reciprocity of imaging and naming, and their relation to constructs associated with distinct phases of referential processing.

Adult↗
PubMed1988

Novel non-templated nucleotide addition reactions catalyzed by procaryotic and eucaryotic DNA polymerases.

DNA polymerases catalyze the addition of deoxyribonucleotides onto DNA primers in a template-directed manner. The requirement for template instruction distinguishes these enzymes from other nucleotidyl transferases, such as terminal deoxynucleotidyl transferase, that do not utilize a template. An oligonucleotide substrate was used to characterize a novel, non-templated nucleotide addition reaction carried out by DNA polymerases from a variety of procaryotic and eucaryotic sources. The products of the reaction, in which a deoxyribonucleotide was added to the 3' hydroxyl terminus of a blunt-ended DNA substrate, were analyzed by electrophoresis on high resolution, denaturing polyacrylamide gels. DNA polymerase from Thermus aquaticus, polymerase alpha from chick embryo, rat polymerase beta, reverse transcriptase from avian myeloblastosis virus, and DNA polymerase I from Saccharomyces cerevisiae all carried out the blunt-end addition reaction. The reaction required a duplex DNA substrate but did not require coding information from the template strand. These results demonstrate that template instruction is not an absolute requirement for the catalysis of nucleotidyl transfer reactions by DNA polymerases.

Animals↗
PubMed1988

Does phospholipase C inhibit fusion between hamster sperm and zona-free eggs?

Previous studies (Hirao and Yanagimachi: Gamete Res. 1:3-12, 1978) have found that phospholipase C (PLC) preparations inhibit sperm-egg fusion. We have attempted to duplicate these results with PLC, as well as with a more specific enzyme, phosphatidylinositol-specific PLC. PLC preparations were applied externally to zona-free hamster eggs prior to incubation with sperm. Phosphatidylinositol-specific PLC did not inhibit sperm penetration. The degree of sperm-egg fusion observed after egg exposure to PLC, however, was dependent upon the purity of the commercial preparation. An impure sample of PLC inhibited sperm penetration, while a more purified preparation did not. The morphology of eggs was unaffected by exposure to phosphatidylinositol-specific PLC and the more purified PLC preparation. The impure preparation, however, was disruptive primarily to the egg plasma membrane as well as to internal organelle organization. The degree of damage by the impure PLC preparation was concentration dependent. The results suggest that as purity of the PLC preparation is increased, the adverse effects of PLC on sperm-egg fusion become negligible.

Animals↗
PubMed1988

In vivo depression of reserve albumin binding capacity by cadmium: a preliminary evaluation.

The effect of cadmium upon the depression of reserve albumin binding capacity (%RABC) was investigated in male, New Zealand white rabbits at daily dosages of 0.65 mg and 0.90 mg Cd/kg body weight. Correlations of % RABC to the duration of exposure were strongest at the higher dosage. After 30-35 days exposure, the decline in % RABC was partially reversed. Levels of total protein in urine increased sharply within a few days after the % RABC had been reduced by cadmium to their lowest values.

Animals↗
PubMed1988

Pulmonary limits of oxygen tolerance in man.

As part of a comprehensive study of specific organ oxygen tolerance [1-4], oxygen effects on pulmonary function were measured in normal, resting men who breathed oxygen continuously at 3.0, 2.5, 2.0, and 1.5 atmospheres absolute (ATA) for average durations of 3.4, 5.7, 9.0, and 17.7 h, respectively. Rates of development of effects of pulmonary oxygen toxicity were monitored during oxygen exposure at 2.5, 2.0, and 1.5 ATA with repeated flow-volume loops, spirometry, and symptom assessment. Additional pulmonary measurements before and after exposure included lung compliance, airway resistance, density dependence of flow, nitrogen closing volumes, carbon monoxide diffusing capacity, and alveolar-arterial oxygen differences. Of these measurements only airway resistance and closing volumes were not significantly affected at any pressure, but patterns and magnitudes of effects varied at different pressures. Overall, the data indicate that continuous oxygen exposure at 3.0 to 1.5 ATA affects pulmonary mechanical function earlier and more prominently than CO diffusing capacity. Recovery of lung mechanical function usually occurred within 12-24 h after exposure, but required more than 24 h in some individuals. No individual measure of pulmonary function was found to be uniquely satisfactory for monitoring rates of development or reversal of pulmonary oxygen poisoning. The existence of multiple pulmonary effects of oxygen toxicity and the complexity of their interactions require selective applications of individual toxicity indices to specific conditions of exposure and recovery.

Atmospheric Pressure↗
PubMed1988

Lysobactin, a novel antibacterial agent produced by Lysobacter sp. II. Biological properties.

Lysobactin, an antibiotic isolated from a strain of Lysobacter, is 2 to 4-fold more active than vancomycin against aerobic and anaerobic Gram-positive bacteria. Included in the spectrum of lysobactin are Staphylococci, Streptococci, corynebacteria, clostridia and various other Gram-positive anaerobic bacteria. The activity of lysobactin against aerobic and anaerobic Gram-negative bacteria is poor. When given parenterally the compound was efficacious in systemic staphylococcal and streptococcal infections in mice. Similarly, when applied topically lysobactin was also curative in a staphylococcal wound infection in mice. Some studies on the mode of action of lysobactin are presented.

Animals↗