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Biomedical subjects

S Daniels

Publications and source records attributed to S Daniels.

At least 55 records · Page 3Linked to original sources
PubMed1993

The effect of high pressure on glycine- and kainate-sensitive receptor channels expressed in Xenopus oocytes.

The effect of high pressure on the response to glycine or kainate of voltage-clamped Xenopus oocytes micro-injected with messenger-RNA derived from either rat spinal cord or whole brain, respectively, has been investigated. Current responses were measured at 1 bar (= 10(5) Pa), 50 bar, 100 bar and 150 bar, with PO2 fixed at 1 bar and the balance helium. Glycine elicited a depolarizing current response which was antagonized by nanomolar concentrations of strychnine. The responses reversibly desensitized, with a decay constant of 0.01 s-1, when glycine concentrations greater than 250 microM were used. The decay constant was insensitive to both glycine concentration and pressure. Resensitization was complete within 4 min. Kainate elicited a depolarizing current which was non-desensitizing. The response was slightly sensitive to glutamate diethyl ester (50 microM), which increased the EC50 by 25%. The action of glycine was highly pressure sensitive. The dose-response curves established at 50 bar, 100 bar and 150 bar were shifted progressively to the right, with no effect on the maximal current. The EC50 increased from 216 microM to 296 microM at 50 bar, to 345 microM at 100 bar, and to 425 microM at 150 bar. The action of kainate was unaffected by pressure. No shift in the dose-response curves was established, nor was there any effect on the maximum current. The EC50 was 113 microM at 1 bar, and 111 microM at both 50 bar and 100 bar.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effects of population density and cadmium toxicity on growth and survival of blowflies.

The blowfly Lucilia sericata has been reared on artificial diets containing from 0 to 200 mg Cd kg(-1) at population densities ranging from 8 larvae per 4-g diet to 8 larvae per 32-g diet. Peak larval weight, development period, pupal weight, adult-emergence weight, and fecundity were measured. Larvae of blowflies respond to food deprivation by a reduction in larval weight and subsequent pupal and adult size. Contaminating the food supply with cadmium produced similar additive effects, reduced the growth rate, and increased the age of pupation. The results are of importance in determining the effects of environmental pollutants on population dynamics.

Journal Article↗
PubMed1993

Does the protein kinase C pathway modulate sarcolemma damage and the release of cytosolic proteins in the rat heart?

1. The release of creatine kinase (CK) in the Langendorff-perfused rat heart during the Ca(2+)-paradox, was critically dependent on the duration and [Ca2+]o of the initial Ca(2+)-depletion phase. 2. When [Ca2+]i was raised by perfusion with caffeine or under N2, activation of the protein kinase C pathway (PKC) produced a small but significant release of CK. PKC stimulation is therefore able to substitute for the Cao(2+)-depletion of the Ca(2+)-paradox. 3. The PKC inhibitor, 1-(5-isoquinolinyl sulphonyl)-2-methyl piperazine, (2 x 10(-6) M) inhibited both the Ca(2+)-paradox and caffeine-induced release of CK. 4. It is concluded that the PKC pathway has a regulatory role for the damage system of the sarcolemma that is responsible for the release of cytosolic proteins.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1993

Biochemical pathways of cell damage during the oxygen paradox of the rat heart.

1. The standard O2-paradox has been studied in the Langendorff-perfused rat heart. 2. Perfusion of glucose-free saline under anoxia did not cause release of creatine kinase (CK) although, it is suggested, there was a progressive rise in [Ca2+]i. 3. Ca(2+)-depletion after anoxia caused CK release. 4. Prolonged anoxic perfusion (55 min) produced a markedly reduced release of CK on Ca(2+)-depletion because, it is suggested, of the reduction in substrates for the release mechanism. 5. No protection against the O2-paradox was found with oxygen radical scavengers and inhibitors. 6. Lowering [Ca2+]o during reoxygenation to 0.1 mM did not reduce CK release. 7. Neither 1 mM amiloride (Na+/H+ antiporter inhibitor) nor 2 x 10(-6) M 1-(5-isoquinolinesulphonyl) piperazine (protein kinase C inhibitor) reduced CK release, unlike their effects in the Ca(2+)-paradox. 8. An hypothesis for events in the O2-paradox in presented: anoxia causes a loss of Ca(2+)-homeostasis and a rise in [Ca2+]i thereby activating a transmembrane NAD(P) oxido-reductase/diaphorase (stage 1); the return of O2 synergistically activates this molecular complex and causes CK release (stage 2).

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1993

Interaction of H2O2 and dithiothreitol and the genesis of cellular damage in the perfused rat heart.

1. H2O2 (0.3 mM) causes release of creatine kinase (CK) from the perfused rat heart, but only when activated by removal of extracellular Ca2+. 2. Dithiothreitol (DTT), 2 mM, provides partial protection against this damage induced by artificially-introduced O2 radicals. 3. Paradoxically, DTT triggers CK release by H2O2 in the presence of extracellular Ca2+. The interaction of these agents in stimulating and protecting against this damage to the sarcolemma is discussed.

Animals↗
PubMed1993

Cellular damage in the rat heart caused by caffeine or dinitrophenol.

1. Langendorff-perfusion of rat hearts with either 10 mM caffeine or 1 mM 2,4-dinitrophenol (DNP) caused severe ultrastructural damage to the myofilaments and mitochondria that was similar to that found in a standard Ca(2+)-paradox. 2. This damage occurred in the presence and absence of extracellular Ca2+. 3. Creatine kinase (CK) release (indicative of sarcolemma breakdown) was not recorded unless the caffeine- or DNP-perfusion was preceded by Ca(2+)0-depletion. 4. It is concluded that: (i) the pathways leading to damage to the myofilaments and sarcolemma are independent; (ii) the CK release mechanism requires dual activation of Ca(2+)0-depletion plus a rise in [Ca2+]i; and (iii) current theories concerning the mechanisms underlying the genesis of the Ca(2+)-paradox are incorrect or incomplete.

2,4-Dinitrophenol↗
PubMed1993

Clinical aspects of malignant mesothelioma in Australia.

Australia is currently experiencing an epidemic of malignant mesothelioma. The clinical aspects of malignant mesothelioma were investigated in 295 Australian patients as part of a national study of the disease. Most patients were male (91%), with the mean age at diagnosis being 64 years. The predominant cell type was epithelial (38%) and the majority of primary tumours arose from the pleura (94%). Mean survival was poor (17.6 months from first symptom; 11.8 months from diagnosis). Patients with a pleural primary tumour were more likely to present with dyspnoea, chest pain and cough; to have a pleural effusion diagnosed radiologically; and to have metastatic spread. Patients with a peritoneal primary tumour were more likely to present with weight loss, loss of appetite, abdominal pain and ascites; to have radiologic evidence of asbestos exposure; and to have spread along a needle track created during a diagnostic tap. A minority of patients had past thoracic conditions, or radiologic findings, specifically related to previous asbestos exposure. About one fifth of patients had no known asbestos exposure. Forty-one per cent of subjects received some form of chemotherapy, radiotherapy and/or surgery, but no formal disease staging had been documented for any patient. Proper controlled trials of secondary and tertiary treatments in malignant mesothelioma are now needed.

Aged↗
PubMed1992

Discordant segregation of Na+,K(+)-adenosine triphosphatase alleles and essential hypertension.

OBJECTIVES: To determine whether the alpha 2 and or beta 1 isoforms of the Na+,K(+)-adenosine triphosphatase (Na+,K(+)-ATPase) are involved in the pathogenesis of essential hypertension. DESIGN: Segregation analysis of polymorphic DNA markers was used to test the involvement of Na+,K(+)-ATPase in essential hypertension. PARTICIPANTS: Children with persistent hypertension having one parent with essential hypertension were included in the study. Criteria for persistent hypertension were blood pressure readings with systolic and/or diastolic levels exceeding the 95th percentile based upon age and sex. The diagnosis of hypertension for adults, including parents and older siblings, was confirmed using criteria recommended in the 1988 report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. RESULTS: In three essential hypertensive families consisting of 18 members including 11 hypertensives, several obligate recombinants between the Na+,K(+)-ATPase alpha 2 isoform marker and the hypertension phenotype were observed. Similarly, in one hypertension family consisting of four members, obligate recombinants between the beta 1 isoform marker and the disease were observed. CONCLUSIONS: The discordant segregation of the alpha 2 and beta 1 isoform markers and essential hypertension suggests that neither the Na+,K(+)-ATPase alpha 2 nor beta 1 isoform genes play a primary role in the pathogenesis of hypertension in the families studied.

Adult↗
PubMed1991

Sonoluminescence in water and agar gels during irradiation with 0.75 MHz continuous-wave ultrasound.

Free radicals, detected as light emissions (sonoluminescence), can be produced in both simple aqueous systems and agar gels by irradiation with 0.75 MHz continuous-wave (CW) ultrasound using acoustic pressures as low as 200 KPa. Although the acoustic pressures necessary for free radical formation in tap water gels (200 KPa), are considerably higher than those required for the formation of macroscopic visible bubbles (26 KPa), the sonoluminescence threshold (0.5 W/cm-2 SATA equivalent) falls at the lower end of the intensity range (0.5-3 W/cm-2) commonly used by ultrasonic physiotherapy equipment. In respect of the overall features of cavitation processes, agar gels appear to be suitable simple systems in which to model cavitation in vivo. However, cavitation processes leading to sonoluminescence are themselves complex as illustrated by the findings that small changes in ionic composition or pH have a significant effect on both the acoustic pressure threshold and the extent of sonoluminescence above this threshold.

Agar↗
PubMed1991

A simple larval diet for population studies on the blowfly Lucilia sericata (Diptera: Calliphoridae).

1. A simple artificial diet was devised for larvae of Lucilia sericata Meigen. 2. A basic diet of 20 g/l agar with 20% horse blood and added yeast sustained normal growth and development, as compared with a lamb meat control. 3. When yeast was added to the blood agar diet at 50 g/l, both peak and final larval weights were increased by 25-50% at higher larval densities (2-8 larvae/g diet) and the hatchling-adult development period was reduced by about 3 days. 4. No adult insects emerged on an agar-yeast diet without blood. Increasing the concentration of blood from 10% to 20% increased adult weight at emergence by 50%, though developmental period was not significantly affected. 5. Increasing larval density significantly reduced the weights of pupae and emergent adults (by up to 50%), both on the blood-agar-yeast diet and the lamb meat control. Percentage survival fell from 80-90% to below 10% on the blood-agar-yeast diet at the highest densities of 4 or 8 larvae/g diet, though survival on lamb was not significantly affected by density.

Analysis of Variance↗
PubMed1991

Effects of general anesthetics and pressure on mammalian excitatory receptors expressed in Xenopus oocytes.

The effects of general anesthetics and pressure on receptors from the mammalian central nervous system have been investigated using oocyte expression techniques. Poly A+ mRNA extracted from rat whole brain was injected into mature Xenopus oocytes producing depolarizing responses to the fast excitatory neurotransmitters NMDA and kainate and the inhibitory neurotransmitters GABA and glycine. An apparatus was constructed to allow agonist dose-response curves to be determined at high pressures using voltage-clamped oocytes. This was used to investigate the excitatory transmitter kainate. It was found that anesthetics depress the current induced by kainate whereas pressure does not appear to affect the responses associated with this transmitter. Furthermore it was found that pressure does not reverse (or modify in any way) the changes in response brought about by application of anesthetics.

Animals↗
PubMed1991

Pulmonary edema due to extreme left atrial compression.

Pulmonary edema is a common concomitant of valvular heart disease and ventricular dysfunction. In addition, left atrial dysfunction due to thrombus, myxoma, or cor triatriatum can produce the same clinical picture. We encountered a patient with intractable pulmonary edema secondary to obliteration of the left atrial cavity by an extrinsically compressing lung tumor. We believe extrinsic compression of the left atrium caused impaired left atrial filling, leading to pulmonary venous hypertension and pulmonary edema.

Atrial Function, Left↗