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Biomedical subjects

W J Morrison

Publications and source records attributed to W J Morrison.

34 records · Page 2Linked to original sources
PubMed1989

Antagonism of platelet activating factor receptor binding and stimulated phosphoinositide-specific phospholipase C in rabbit platelets.

The objective of this study was to establish whether binding of platelet activating factor (PAF) to its receptor was integral to the stimulation of phosphoinositide-specific phospholipase C (PLC) in rabbit platelets. Saturation binding curves for [3H]PAF indicated that the PAF receptor has a dissociation constant (KD) of 28.72 nM. In comparison, PAF-stimulated PLC activity, as monitored by [3H]inositol triphosphate production, increased at lower concentrations and had an half-maximal effective concentration (EC50) value of 1.5 nM. Unlabeled PAF inhibited [3H]PAF binding competitively and demonstrated two binding sites, a high affinity site with an inhibitory constant (Ki) of 2.65 nM and a low affinity site with a Ki of 0.80 microM. The inhibitory effects of four PAF antagonists, CV-3988, CV-6209, SRI 63-441 and SRI 63-675 on the binding of [3H]PAF were compared to the effects of the antagonists on PAF-stimulated PLC activity. The four antagonists inhibited [3H]PAF binding almost completely whereas their ability to inhibit PAF-stimulated PLC activity varied. CV-3988, SRI 63-441 and SRI 63-675 had half-maximal inhibitory concentration (IC50) values of 0.28, 0.78 and 0.42 microM, respectively, whereas CV-6209 was more potent at inhibiting [3H]PAF binding (IC50 = 7.73 nM). The SRI 63-441 and SRI 63-675 inhibited PLC totally with an IC50 value of 0.78 and 1.27 microM, respectively. The CV-3988 and CV-6209 showed a maximal PLC inhibition of about 45% with "apparent IC50" values of 1.05 and 0.17 microM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Transbilayer effects of ethanol on fluidity of brain membrane leaflets.

Previous work on membrane effects of ethanol focused on fluidization of the bulk membrane lipid bilayer. That work was extended in the present study to an examination of ethanol's effect on lipid domains. Two independent methods were developed to examine the effects of ethanol on the inner and outer leaflets of synaptic plasma membranes (SPM). First, differential polarized phase and modulation fluorometry and selective quenching of diphenyl-1,3,5-hexatriene (DPH) were used to examine individual leaflets. Both limiting anisotropy and rotational relaxation time of DPH in SPM indicated that the outer leaflet was more fluid than the inner leaflet. Second, plasma membrane sidedness selective fluorescent DPH derivatives, cationic 1-[4-(trimethylammonio)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH) and anionic 3-[p-6-phenyl)-1,3,5-hexatrienyl]phenylpropionic acid (PRO-DPH), confirmed this transmembrane fluidity difference. TMA-DPH and PRO-DPH preferentially localized in the inner and outer leaflets of SPM, respectively. Ethanol in vitro had a greater fluidizing effect in the outer leaflet as compared to the inner leaflet. Thus, ethanol exhibits a specific rather than nonspecific fluidizing action within transbilayer SPM domains. This preferential fluidization of the SPM outer leaflet may have a role in ethanol affecting transmembrane signaling in the nervous system.

Animals↗
PubMed1988

Desensitization of receptor-coupled activation of phosphoinositide-specific phospholipase C in platelets: evidence for distinct mechanisms for platelet-activating factor and thrombin.

Platelet-activating factor (PAF) receptor-coupled activation of phosphoinositide-specific phospholipase C (PLC) was studied in platelets that were made refractory, by short-term pretreatments, to either PAF or thrombin. Generation of [3H]inositol triphosphate ( [3H]IP3) was monitored specifically for this purpose. [3H]Inositol-labeled rabbit platelets that were incubated (10 min) with increasing concentrations of PAF and subsequently challenged by the same concentration of PAF had greatly diminished PLC activity ( [3H]IP3 production) as compared to controls. Platelets incubated (10 min) with fixed concentrations of PAF and then challenged with increasing concentrations of PAF had log-dose response curves of [3H]IP3 production progressively shifted to the right (i.e., to higher concentrations) and were depressed as the PAF pretreatment with 10 nM PAF became completely refractory to further PAF stimulation of PLC. Washing the pretreated platelets with either buffer or buffer containing 0.5% bovine serum albumin did not restore the PAF for 10 min), platelets remained fully responsive to thrombin (2 units/ml)-stimulated production of [3H]IP3. Platelets pretreated with increasing concentrations of thrombin (0.15-2 units/ml) for different times (5-40 min) became refractory to both thrombin and PAF. It is concluded that PAF receptor-coupled activation of PLC becomes refractory (desensitized) in platelets preexposed to PAF, whereas platelets pretreated with thrombin are desensitized to both thrombin and PAF. It is proposed that thrombin has two transmembrane pathways leading to the activation of PLC, one shared with PAF and another utilizing separate mechanistic inputs.

Blood Platelets↗
PubMed1987

A decision-driven system to collect the patient history.

We have developed a computer-administered history designed to directly interview hospitalized patients with pulmonary disease. A frame-based decision system is used to direct the history and to generate a one- to five-member differential diagnostic list based on this history. This system incorporates a cognitive model of question selection and a Bayesian scoring algorithm. Structures to control the choice of questions are embedded in the diagnostic frames and in a QUERY program that makes the final choice of questions. We have compared the behavior of this decision-driven approach with a history taken using a paper questionnaire. The paper-based history presents 182 questions to every patient and captured 75% of 85 pulmonary diseases in its differential lists. The decision-driven system asks 50.7 +/- 31.0 (mean +/- standard deviation) and captured 74% of 61 pulmonary diseases. Our experience suggests that the use of a computerized diagnostic knowledge base to direct the selection of pertinent questions can substantially reduce the number of questions necessary to collect a diagnostically useful patient history.

Artificial Intelligence↗
PubMed1978

Cytogenetic localization of the acid phosphatase-1 gene in Drosophila melanogaster.

A translocation in which a segment of chromosome 3 is inserted into the Y chromosome was found to contain the acid phosphatase-1 gene (Acph-1). In flies hyperploid for that gene, acid phosphatase-1 levels are proportional to the dose of the gene. The locus is placed within the salivary chromosome subdivisions 99D and 99E on the basis of its inclusion in the translocated segment and on the previous placement of the claret locus. Several chromosomal rearrangements involving heterochromatic breakpoints and euchromatic breakpoints adjacent to 99D-99E were tested for possible postiion-effect variegation of acid phosphatase-1. No decrease in the synthesis of the electorphoretic subunit encoded by the relocated gene was observed within any of the rearrangements.

Acid Phosphatase↗
PubMed1976

Pneumatosis intestinalis in association with connective tissue disease.

Pneumatosis intestinalis in association with connective tissue diseases is an unusual combination whose pathogenesis is not yet understood. Furthermore, steroid medication, often used to treat these diseases, may itself cause pneumatosis. Three cases of scleroderma, systemic lupus erythematosus, and amyloidosis in association with pneumatosis and without prior steroid therapy are presented. The small vessel occlusive pathologic processes in these diseases may cause focal areas of mucosal ischemia resulting in small, perhaps transient ulcerations that allow gas to enter the gut wall from the lumen.

Adult↗
PubMedDate not supplied

Transmembrane signalling associated with ganglioside-induced CD4 modulation.

Ganglioside (GM1) treatment of CD4+ human CEM lymphoma cells stimulated transient phosphoinositide (PI) breakdown, production of inositol phosphates (IP), protein phosphorylation and rapid decrease of CD4 surface expression. A comparison between the actions of GM1 and other agents that affect these signal transduction pathways demonstrated a distinct mechanism for GM1-induced decrease of CD4. GM1 stimulated both phospholipase C activity and protein phosphorylation but had no effect on either cellular cAMP levels or tyrosine kinase activity. Phorbol myristate acetate (PMA) stimulated protein phosphorylation and caused a significant decrease in surface display of CD4. Both of these processes were blocked by pretreating cells with the protein kinase C (PKC) inhibitor H7. These results demonstrate that GM1 stimulates PI turnover and induces a rapid decrease of CD4 surface expression by processes that do not activate adenylate cyclase or tyrosine kinase. They further demonstrate that the mechanism for GM1-induced decrease of CD4 is distinct from the CD4 internalization processes mediated by PKC activity.

Adenylyl Cyclases↗
PubMedDate not supplied

Ganglioside (GM1)-treated T cells shed CD4.

In previous studies (Morrison et al., 1990), we showed that ganglioside (GM1) modulation of CD4 was associated with activation of phospholipase C and increased production of inositol triphosphate, but not with activation of protein kinase C. These results demonstrated a unique signal transduction pathway related to GM1 modulation of CD4 on T cells and raised the question as to whether intracellular Ca2+ levels and related protein kinases would be affected by GM1-induced signalling. We now show that GM1 modulation of CD4 from human T cells corresponds to decreased cellular Ca2+ without significant changes in cellular protein phosphorylation. In the course of this study we discovered that T cells challenged with GM1 exhibited new proteins in their surrounding media. Fractionation of cellular and supernatant proteins show that cells treated with GM1 released proteins with an approximate molecular weight (Mr) of 49,000. This was exclusive of GM1 protein association and GM1-induced protein phosphorylation. Immunoblots demonstrated the presence of CD4 in GM1-treated cell supernatants. Western immunoblots using anti-CD4 antibodies detected a lower Mr form (49,000) of CD4 in the supernatants of GM1-treated cells. These studies further define the unique nature of GM1 signalling relating to modulation of CD4 and demonstrate that the fate of GM1 modulated CD4, in part, involves protein shedding.

CD4 Antigens↗
PubMedDate not supplied

Response to platelet-activating factor in human platelets stored and aged in plasma. Decrease in aggregation, phosphoinositide turnover, and receptor affinity.

Human platelet concentrates were stored in polyolefin bags at 22 to 24 degrees C on a horizontal shaker for up to 8 days. At different intervals, aliquots of platelet-rich plasma (PRP) were removed aseptically and five variables, i.e., platelet counts, morphology, platelet-activating factor (PAF)-stimulated aggregation, phosphoinositide turnover, and [3H]PAF binding to platelet receptors, were studied. The number of platelets did not change during the 8 days of storage. Scanning electron microscopy of the platelets revealed a gradual morphologic change from biconcave flat discs to irregular, crenated forms. The PAF-induced aggregation of platelets declined with time of storage. A decrease to 50 percent of the Day 1 aggregatory response to PAF was evident on Day 2, and there was a further decline to about 20 percent by Day 6. Similarly, PAF receptor-coupled phosphoinositide turnover, as monitored by 32P incorporation into individual phosphoinositides, decreased dramatically with storage. After 2 to 3 days of storage, the phosphoinositide turnover was reduced to 50 percent of the original response, and it continued to decline to about 25 percent of original response by Day 5 or 6. The binding of [3H]PAF to washed human platelets indicated subtle changes between Days 2 and 4, which became more noticeable by Day 6. These results have raised the possibility of changes in the number of the receptors and/or their affinity for the ligand during storage. We conclude that although the number of platelets was maintained during storage for 8 days, a general deterioration of their responses to PAF occurred at the levels of cell surface receptor, transmembrane signaling (phosphoinositide turnover), and response (aggregation).

Binding, Competitive↗
PubMedDate not supplied

Revision of diagnostic logic using a clinical database.

Statistical pattern-recognition techniques have been frequently applied to the problem of medical diagnosis. Sequential Bayesian approaches are appealing because of the possibility of generating the underlying sensitivities, specificities, and prevalence statistics from the estimates of medical experts. The accuracy of these estimates and the consequences of inaccuracies carry implications for the future development of this type of system. In an effort to explore these subjects, the authors used statistics derived from a clinical database to revise the diagnostic logic in a Bayesian system for generating a differential diagnostic list. Substantial changes in estimated a priori probabilities, sensitivities, and specificities were made to correct for significant under- and overestimations of these values by a group of medical experts. The system based on the derived values appears to perform better than the original system. It is concluded that the statistics used in a Bayesian diagnostic system should be derived from a database representative of the patient population for which the system is designed.

Bayes Theorem↗