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Biomedical subjects

K R Parker

Publications and source records attributed to K R Parker.

At least 19 recordsLinked to original sources
PubMed1991

Spectrophotometric quantitation of rhodopsin in the human retina.

The rhodopsin content of the human retina was determined spectrophotometrically. Retinas were removed completely by using an in vitro technique based on a simulation of retinal detachment. This method provides a total recovery of rod outer segments which contain the rhodopsin visual pigment or its apoprotein, opsin. Using this improved dissection method followed by a crude preparation of the retina, an opsin-rhodopsin content of 6.20 +/- 0.64 nmol/retina (n = 9) was found. This is larger than values previously reported. Regeneration with a threefold excess of 11-cis-retinal improved the recovery of rhodopsin dramatically because the corneas of these human donor eyes were removed for corneal transplant surgery under relatively bright light that bleaches the retina nearly completely. The amount of rhodopsin that can be isolated will be sufficient for studies on early events in visual transduction using laser photolysis.

Adult↗
PubMed1990

Antimutagenesis in yeast by sodium chloride, potassium chloride, and sodium saccharin.

Aqueous salt solutions containing NaCl, KCl, MgCl2, Na2SO4, CaCl2, NH4Cl, or sodium saccharin are mutagenic in yeast when logarithmic growth of cells is interrupted by exposure to a 0.5-2.0 M salt solution. Stationary-phase cells are not mutated by this treatment. When placed in an enriched medium with the salt, the stationary-phase cells grow after a prolonged lag period. The compounds tested (NaCl, KCl, and sodium saccharin), under conditions in which growth in medium can take place, exhibit an antimutagenic response as measured by the compartmentalization test. The antimutagenic action of salt solutions in yeast is concentration-dependent. Unlike the mutagenic action of these compounds, which approximates an osmolality-dependent response, the antimutagenic action seems to be correlated with toxicity as measured by growth rate reduction at increasing concentrations of the compounds. For example, sodium saccharin and NaCl exhibit almost identical osmolalities; however, 0.3 M sodium saccharin reduces the growth rate much more than does 0.3 M NaCl. At these same molar concentrations, the spontaneous mutation rate for histidine prototrophy is, for the control, 6.2 x 10(-8) mutations/cell/-generation, 3.5 x 10(-8) with 0.3 M NaCl, and 1.7 x 10(-8) with 0.3 M sodium saccharin.

Depression, Chemical↗
PubMed1989

Nuclear worries of Canadian youth: replication and extension.

A national survey of Canadian adolescents assessed concern, anxiety, and sources of information about the threat of nuclear war. Results indicated few geographical or gender differences in overall levels of concern, although females were more likely to admit fear and anxiety, and students with activist parents showed more concern. Family ranked below all media as a source of information.

Adolescent↗
PubMed1987

Retinal rod GTPase turnover rate increases with concentration: a key to the control of visual excitation?

Guanosine triphosphate (GTP) binding proteins mediate cellular responses to hormones, neurotransmitters, growth factors and light. Activated GTP binding proteins are shut off by GTPase mediated hydrolysis of GTP. Photoreceptor GTPase rates are reported to be 10-50 times too slow to account for electrophysiological recovery time after light stimulus. Recovery rates of other parts of the system, however, appear fast enough. We present evidence that the GTPase rate increases markedly with photoreceptor membrane concentration implying the existence of a diffusible factor controlling the GTPase. When extrapolated to physiological concentrations, the GTPase turnover rate is fast enough (0.25-1.5 sec) to account for the recovery rate of the light stimulated signal of the photoreceptor cells.

Animals↗
PubMed1987

Mg2+-ATP induces filament growth from retinal rod outer segments with disrupted plasma membranes.

Mg2+-ATP produces a large decrease in near-IR light scattering when added to suspensions of rod outer segments (ROS) when the plasma membranes have been disrupted by a gentle dialysis procedure. When this process is studied by light microscopy with video-enhanced image contrast, the Mg2+-ATP-dependent signal is seen to be associated with the formation of filaments which extend only from those ROS lacking plasma membranes. Both the IR light scattering signal and filament growth are inhibited by vanadate and DCCD but not by colchicine, colcemid or cytochalasins.

Actin Cytoskeleton↗
PubMed1987

Base-substitution and frameshift mutagenesis by sodium chloride and potassium chloride in Saccharomyces cerevisiae.

Sodium chloride (NaCl) and potassium chloride (KCl) are both capable of inducing lethality and mutations when each is administered at a molarity of two for different lengths of time to logarithmic phase cells of the yeast Saccharomyces cerevisiae. Analysis of the revertants indicates that the reversions can be base substitutions, of both the transition and the transversion type, as well as frameshift mutations. At equal molarity, with the frequency of mutations as the criterion, KCl and NaCl are equally efficient in inducing all types of mutations.

Cell Survival↗
PubMed1985

Thinking about the threat of nuclear war: relevance to mental health.

Ontario students in grades 7-13 responded to open-ended and multiple-choice questions about future concerns, particularly unemployment, job/career plans, and the nuclear threat. Although worries about nuclear war were more frequent than those in other areas, their expression was associated with a sense of social efficacy rather than with feelings of helplessness.

Adolescent↗
PubMed1981

Two platelet aggregation inhibitors in tsetse (Glossina) saliva with studies of roles of thrombin and citrate in in vitro platelet aggregation.

Two inhibitors of platelet aggregation have been identified in saline extracts of Glossina morsitans (tsetse) salivary glands. A protein fraction (MW greater than 30 000) inhibited primary and secondary aggregation to ADP, secondary aggregation to adrenalin, and aggregation to collagen. It also caused disaggregation of platelets stimulated by ADP and adrenalin. These properties could be explained by ADP hydrolytic activity. A previously identified antithrombin fraction (MW 11 000-13 000) abolished thrombin-induced aggregation. It did not affect platelet aggregation to ADP, adrenalin or collagen, as compared to aggregation in citrate, when used as sole anticoagulant for platelet rich plasma or when added to citrated platelet rich plasma. These results fail to support hypotheses (i) that thrombin plays an important role in platelet aggregation by other agonists and (ii) that secondary platelet aggregation is an artefact induced by citrate. It is proposed that these inhibitors may be important in maintaining mouthpart and crop patency during feeding. Their discovery suggests that other arthropods may also have antiplatelet agents in their saliva which might be entomologically important, provide useful tools for platelet studies, and be of potential therapeutic interest.

Animals↗
PubMed1980

Rubella antibody titres and immunization status in a family practice.

Rubella vaccination status and immunity to rubella were studied in 230 "active patients" aged 8 to 22 years in a teaching family practice by means of a chart review and measurement of the rubella antibody titre in a blood sample. Of the 200 patients who submitted a blood sample 161 (80%) were found to be immune, having a rubella hemagglutination-inhibiting antibody titre of 1:16 or greater. Log linear analysis showed that immunity to rubella was independent of a history of rubella, and that 94% of the vaccinated patients versus 74% of the unvaccinated patients (a significant difference; P = 0.007) were immune. In retrospect we estimated that 80% of the study group were protected at the start of the study. After surveillance and follow-up, with vaccination of 27 of the 39 patients identified as susceptible to rubella, this estimated proportion increased to 90%. The study showed that there is nothing to be gained by asking about a history of rubella but that vaccination against this disease is increasing among children aged 5 to 9 years.

Adolescent↗
PubMed1979

Effects of tsetse (Glossina morsitans morsitans Westw.) (Diptera: Glossinidae) salivary gland homogenate on coagulation and fibrinolysis.

The saliva of the tsetse, Glossina morsitans morsitans Westwood, has antithrombin anticoagulant activity and inhibits thrombin's esterolytic activity. It has no other detectable anticoagulant properties. The anticoagulant elutes in a single peak on Sephadex fraction, is immediately acting, heat and storage stable, and has a molecular weight of 11-13,000. Unlike heparin it is not neutralized by protamine sulphate or toluidine blue and does not require the co-factor, antithrombin III, for optimal anticoagulant activity. It has similar properties to hirudin, but does not elute with a protein peak upon Sephadex fractionation and has a slightly different molecular weight. Salivary gland homogenates contained neither a plasminogen activator nor fibrinolytic activity. The sera of rabbits used to maintain tsetses, which contained precipitating antibodies against saliva, did not neutralize the salivary anticoagulant in vitro. The properties of this anticoagulant suggest that it might be a potentially useful antithrombotic agent in man.

Animals↗
PubMed1979

Electromyographic changes reviewed in chronic spinal arachnoiditis.

A retrospective study was done to determine if specific electromyographic findings are present in spinal arachnoiditis. The electromyographic (emg) findings in 32 surgically and 35 myelographically diagnosed cases were examined. The cases were categorized into 3 groups. The 1st groups consisted of 37 cases with surgical or myelographic evidence believed to be highly diagnostic of multilevel chronic spinal arachnoiditis. The 2nd group was composed of 23 cases with surgical or myelographic evidence consistent with a localized problem. The 3rd group was a control group with normal or minimal changes on myelography or at surgery. Electromyographic findings were divided into 3 groups of changes: localized, nonlocalized or normal. Localized emg changes were considered to be present over 2 or less root levels in either or both anterior or posterior primary ramus distribution. Nonlocalized changes occurred over more than 2 such levels. A comparative analysis of the myelographic and surgical findings with the emg changes indicated that there was not diagnostic emg picture indicative of chronic spinal arachnoiditis.

Arachnoiditis↗
PubMed1978

Some effects of uninfected laboratory-reared tsetses (Glossina morsitans morsitans westw.) (diptera: glossinidae) on host-rabbits.

Rabbits (Flemish giant x French lop-eared) exposed to 300 to 500 tsetses (Glossina morsitans morsitans Westw.) a day, 2 or 3 days a week, did not show significant differences from littermates receiving no exposure, with respect to weight changes, haematocrits, red and white blood cell counts or whole blood clotting times. In other rabbits, the same daily exposure, 6 days a week, resulted in sharp decreases in haematocrit levels and in some, changes in weights, but no change in citrated plasma thrombin times. Rabbit haematocrit levels correlated negatively with estimated weekly blood loss. Weights and haematocrits of most rabbits exposed to 1,200 to 1,500 flies on a single occasion were not affected. However, following heavy exposure, ears were cold and blood letting difficult, indicating the possibility of arteriolar vasoconstriction.

Animals↗
PubMed1970

Natural history of isolated patent ductus arteriosus and the effect of surgical correction: twenty years' experience at The Hospital for Sick Children, Toronto.

Seven hundred and forty-four cases of patent ductus arteriosus were diagnosed at The Hospital for Sick Children, Toronto, in the 20-year period from 1947 to 1966. Of these 705 have been treated surgically. It is concluded that operation is best performed between 6 and 12 months of age. Isolated ductus arteriosus is rarely a cause of congestive heart failure, and is more likely to be so in the presence of the rubella syndrome. Failure associated with the anomaly in the neonatal period can usually be successfully managed by medical treatment. Spontaneous closure after one month of age is not to be expected. Surgical treatment at the appropriate time prevents the subsequent development of Eisenmenger's complex.

Adolescent↗