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Biomedical subjects

R R Powell

Publications and source records attributed to R R Powell.

8 recordsLinked to original sources
PubMed2006

Entamoeba histolytica: comparison of the role of receptors and filamentous actin among various endocytic processes.

Entamoeba histolytica is the causative agent of amoebic dysentery. Uptake of iron is critical for E. histolytica growth and iron-bound human transferrin (holo-transferrin) has been shown to serve as an iron source in vitro. Although a transferrin-binding protein has been identified in E. histolytica, the mechanism by which this iron source is taken up by this pathogen is not well understood. To gain insight into this process, the uptake of fluorescent-dextran, -holo-transferrin, and human red blood cells (hRBCs) was compared. Both dextran and transferrin were taken up in an apparent receptor-independent fashion as compared to hRBCs, which were taken up in a receptor-mediated fashion. Interestingly, the uptake of FITC-dextran and FITC-holo-transferrin differentially relied on an intact actin cytoskeleton suggesting that their internalization routes may be regulated independently.

Actins↗
PubMed2006

Entamoeba histolytica: FYVE-finger domains, phosphatidylinositol 3-phosphate biosensors, associate with phagosomes but not fluid filled endosomes.

Endocytosis is an important virulence function for Entamoeba histolytica, the causative agent of amoebic dysentery. Although a number of E. histolytica proteins that regulate this process have been identified, less is known about the role of lipids. In other systems, phosphatidylinositol 3-phosphate (PI3P), a product of phosphatidylinositol 3-kinase (PI 3-kinase), has been shown to be required for endocytosis. FYVE-finger domains are protein motifs that bind specifically to PI3P. Using a PI3P biosensor consisting of glutathione-S-transferase (GST) fused to two tandem FYVE-finger domains, we have localized PI3P to phagosomes but not fluid-phase pinosomes in E. histolytica, suggesting a role for PI3P in phagocytosis. Treatment of cells with PI 3-kinase inhibitors impaired GST-2 x FYVE-phagosome association supporting the authenticity of the biosensor staining. However, treatment with PI 3-kinase inhibitors did not inhibit E. histolytica-particle interaction, indicating that PI3P is not required for the initial step, but is required for subsequent steps of phagocytosis.

Androstadienes↗
PubMed1983

Flicker fusion as a typological index of nervous system 'reactivity'.

Flicker fusion responses were determined under varying stimulus intensities for 43 subjects. A mathematical index of the responses was derived for each individual and compared to a single flicker fusion response. A correlation demonstrated independence between the two measures.

Adult↗
PubMed1982

Technique for differentiating cortical hemispheric activity following exercise.

Peripheral Critical Flicker Fusion technology was explored as a basis for inferred differences between right and left cortical hemispheric activity following exercise. 18 subjects underwent three treatments presented in randomized order with 1-wk. intervals in between them. Conditions included a control, 30 min. of steady-state treadmill running, and 20 min. of treadmill running followed by progressively increasing speed until exhaustion intervened. Immediately following each treatment, subjects were given a test of peripheral critical flicker fusion as measured in both peripheral retinal fields. Differences between right and left peripheral retinal field perception were analyzed for the three conditions with a one-way analysis of variance using a repeated-measures design. A significant difference was found among the three treatments for peripheral CFF differences between right and left peripheral fields. A Newman-Keuls test demonstrated a significant shift in cortical activation toward the left hemisphere following the exhaustive exercise. The inferred shift in cortical activity inferred from peripheral CFF, occurs following exhaustive exercise. The left hemisphere was viewed as the dominant locus of cortical activation in that fatigue state.

Adult↗