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Biomedical subjects

P Tong

Publications and source records attributed to P Tong.

At least 19 recordsLinked to original sources
PubMed2000

Insulin-induced actin filament remodeling colocalizes actin with phosphatidylinositol 3-kinase and GLUT4 in L6 myotubes.

We examined the temporal reorganization of actin microfilaments by insulin and its participation in the localization of signaling molecules and glucose transporters in L6 myotubes expressing myc-tagged glucose transporter 4 (GLUT4myc). Scanning electron microscopy revealed a dynamic distortion of the dorsal cell surface (membrane ruffles) upon insulin treatment. In unstimulated cells, phalloidin-labeled actin filaments ran parallel to the longitudinal axis of the cell. Immunostaining of the p85 regulatory subunit of phosphatidylinositol 3-kinase was diffusely punctate, and GLUT4myc was perinuclear. After 3 minutes of insulin treatment, actin reorganized to form structures; these structures protruded from the dorsal surface of the myotubes by 10 minutes and condensed in the myoplasm into less prominent foci at 30 minutes. The p85 polypeptide colocalized with these structures at all time points. Actin remodeling and p85 relocalization to actin structures were prevented by cytochalasin D or latrunculin B. GLUT4myc recruitment into the actin-rich projections was also observed, but only after 10 minutes of insulin treatment. Irrespective of insulin stimulation, the majority of p85 and a portion (45%) of GLUT4 were recovered in the Triton X-100-insoluble material that was also enriched with actin. In contrast, vp165, a transmembrane aminopeptidase that morphologically colocalized with GLUT4 vesicles, was fully soluble in Triton X-100 extracts of both insulin-treated and control myotubes. Transient transfection of dominant inhibitory Rac1 (N17) into L6 myotubes prevented formation of dorsal actin structures and blocked insulin-induced GLUT4myc translocation to the cell surface. We propose that insulin-dependent formation of actin structures facilitates the association of PI3-K (p85) with GLUT4 vesicles and, potentially, the arrival of GLUT4 at the cell surface.

Actins↗
PubMed1999

Role of the actin cytoskeleton in insulin action.

Insulin has diverse effects on cells, including stimulation of glucose transport, gene expression, and alterations of cell morphology. The hormone mediates these effects by activation of signaling pathways which utilize, 1) adaptor molecules such as the insulin receptor substrates (IRS), the Src and collagen homologs (Shc), and the growth factor receptor binding protein 2 (Grb2); 2) lipid kinases such as phosphatidylinositol 3-kinase (PI 3-Kinase); 3) small G proteins; and 4) serine, threonine, and tyrosine kinases. The activation of such signaling molecules by insulin is now well established, but we do not yet fully understand the mechanisms integrating these seemingly diverse pathways. Here, we discuss the involvement of the actin cytoskeleton in the propagation and regulation of insulin signals. In muscle cells in culture, insulin induces a rapid actin filament reorganization that coincides with plasma membrane ruffling and intense accumulation of pinocytotic vesicles. Initiation of these effects of insulin requires an intact actin cytoskeleton and activation of PI 3-kinase. We observed recruitment PI 3-kinase subunits and glucose transporter proteins to regions of reorganized actin. In both muscle and adipose cells, actin disassembly inhibited early insulin-induced events such as recruitment of glucose transporters to the cell surface and enhanced glucose transport. Additionally, actin disassembly inhibited more prolonged effects of insulin, including DNA synthesis and expression of immediate early genes such as c-fos. Intact actin filaments appear to be essential for mediation of early events such as association of Shc with Grb2 in response to insulin, which leads to stimulation of gene expression. Preliminary observations support a role for focal adhesion signaling complexes in insulin action. These observations suggest that the actin cytoskeleton facilitates propagation of the morphological, metabolic, and nuclear effects of insulin by regulating proper subcellular distribution of signaling molecules that participate in the insulin signaling pathway.

Actins↗
PubMed1999

Solid-state characteristics of amorphous sodium indomethacin relative to its free acid.

PURPOSE: Having previously studied the amorphous properties of indomethacin (IN) as a model compound for drugs rendered amorphous during processing, we report on the formation and characterization of its sodium salt in the amorphous state and a comparison between the two systems. METHODS: Sodium indomethacin (SI) was subjected to lyophilization from aqueous solution, rapid precipitation from methanol solution, and dehydration followed by grinding to produce, in each case, a completely amorphous form. The amorphous form of SI was analyzed using DSC, XRD, thermomicroscopy and FTIR. The method of scanning rate dependence of the glass transition temperature, Tg, was used to estimate the fragility of the SI system. Enthalpy relaxation experiments were carried out to probe the molecular mobility of the SI system below Tg. RESULTS: The amorphous form of SI formed by different methods had a Tg equal to 121 degrees C at a scanning rate of 20 degrees C/min. This compares with a Tg for indomethacin of 45 degrees C. Estimation of fragility by the scanning rate dependence of Tg indicates no significant differences in fragility between ionized and unionized forms. Enthalpy relaxation measurements reveal very similar relaxation patterns between the two systems at the same degree of supercooling relative to their respective Tg values. CONCLUSIONS: The amorphous form of SI made by various methods has a Tg that is about 75 degrees C greater than that of IN, most likely because of the greater density and hence lower free volume of SI. Yet, the change of molecular mobility as a function of temperature relative to Tg is not very different between the ionized and unionized systems.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1998

Velocity difference measurement with a fiber-optic coupler.

Two single-mode fibers collect light with the same scattered wave vector from two spatially separated regions in a sample. These regions are illuminated by a single coherent laser beam, so that the collected signals interfere when combined by means of a fiber-optic coupler, before they are directed to a photomultiplier tube. The fibers and the coupler are polarization preserving to guarantee a high signal-to-noise ratio. The measured intensity fluctuations are used to determine the velocity difference omega v(L) for spatial separations L in the sample. Specifically, an intensity autocorrelation function is calculated theoretically for rigid body rotation and is tested experimentally. Experimental results span two orders of magnitude in L and agree with theoretical predictions with an error of less than 5%. This new technique will be very useful in the study of turbulent flow and particle settling dynamics.

Fiber Optic Technology↗
PubMed1997

Deformation-induced hierarchical flows and drag forces in bone canaliculi and matrix microporosity.

Existing theories for interstitial flows in bone have only examined the contributions from different flow systems separately, such as the flows through the microporosity, the canaliculi, and the Haversian canals. An overall model encompassing the hierarchical microstructure is important to our understanding of the actual physics of flows in bone. The flow-induced drag forces and streaming electrical potentials could interact with the osteocytes to effect biological responses. A finite element model was developed to study the contributions from various hierarchical flow channels in bone. Cortical bone is modelled as a fully hydrated biphasic poroelastic material with a superposing network of one-dimensional channels radiating from the Haversian canals representing the canaliculi. Interfacial cross-flows between these one-dimensional channels and the neighbouring poroelastic matrix are driven by the pressure differences between the matrix and the channel. The model was subjected to stress fields simulating uniform compression and pure bending. The effects of the interfacial permeability and the solid content within the channels on the drag forces in the channels were assessed. Abrupt changes in these drag forces occurred as the channel solidity approached that of the microporosity. The results were quite sensitive to the interfacial permeability, i.e. the interconnectivity between the canalicular system and the matrix microporosity. This biomechanical model should be useful to the study of mechanotransduction in bone.

Biomechanical Phenomena↗
PubMed1997

Insulin resistance in adult polycystic kidney disease.

Adult polycystic kidney disease (APKD) is a common hereditary disease with renal and extra-renal manifestations. There are at least three genes responsible for this disease. The polycystic kidney disease 1 (PKD1) gene product is a membrane protein involved in cell-cell and cell-matrix interactions and has a widespread tissue distribution. Abnormal membrane fluidity in erythrocytes from APKD patients is due to altered membrane proteins. Membrane fluidity of mononuclear cells is related to whole body insulin sensitivity. Insulin sensitivity might therefore be disturbed in APKD if the erythrocyte membrane abnormality is also present in other cells. Therefore, we investigated insulin sensitivity in 15 APKD patients and 20 normal subjects matched for age and sex. Insulin sensitivity was assessed by a short insulin tolerance test to derive the first-order rate constant for the disappearance of glucose (Kitt) and mononuclear leukocyte membrane fluidity was measured by fluorescence anisotropy. The Kitt value (% mmol.liter-1.min-1) was lower in APKD patients than in normal subjects [median (range) 2.2 (1.5 to 6.3) vs. 4.1 (2.0 to 5.4). P < 0.001]. Fasting plasma insulin concentrations were negatively correlated with the Kitt values (r = -0.66, P < 0.001). Core region anisotropy was significantly lower (higher fluidity) in leukocytes from APKD patients [mean (SEM) 0.164 (0.003) vs. 0.174 (0.001), P < 0.001]. Insulin sensitivity was positively correlated with the fluorescence anisotropy of the core region of leukocyte membranes (r = 0.81, P = 0.0001). In conclusion, APKD patients were insulin resistant and some patients were hyperinsulinemic, which may indicate increased cardiovascular risk. The cellular basis of the insulin resistance may be directly related to the proteins causing the disease or to the general change in membrane properties.

Adolescent↗
PubMed1996

Fibroblast growth factor (FGF) homologous factors: new members of the FGF family implicated in nervous system development.

Four new members of the fibroblast growth factor (FGF) family, referred to as fibroblast growth factor homologous factors (FHFs), have been identified by a combination of random cDNA sequencing, data base searches, and degenerate PCR. Pairwise comparisons between the four FHFs show between 58% and 71% amino acid sequence identity, but each FHF shows less than 30% identity when compared with other FGFs. Like FGF-1 (acidic FGF) and FGF-2 (basic FGF), the FHFs lack a classical signal sequence and contain clusters of basic residues that can act as nuclear localization signals. In transiently transfected 293 cells FHF-1 accumulates in the nucleus and is not secreted. Each FHF is expressed in the developing and adult nervous systems, suggesting a role for this branch of the FGF family in nervous system development and function.

Adult↗
PubMed1996

Erythrocyte membrane fluidity in adult polycystic kidney disease: difference between intact cells and ghost membranes.

In adult polycystic kidney disease (APCKD) the cytoskeleton of renal tubular cells is abnormal. In erythrocytes the cytoskeleton affects the fluidity of membrane lipids. The authors determined fluorescence anisotropy in intact erythrocytes and erythrocyte ghosts in 12 APCKD patients and 12 normal subjects. In APCKD whole erythrocytes had a much lower core-region anisotropy, which indicated higher membrane fluidity than normal (mean 0 center dot 175 vs. 0 center dot 224, P < 0 center dot 01). This abnormality was not detected in erythrocyte ghosts, which suggests that preparation of ghosts altered membrane lipid organization. This could be directly due to ghosting or secondary to the loss of cytoskeletal effects, which may be abnormal in APCKD.

Adolescent↗
PubMed1996

Herpes simplex virus infection masquerading as condyloma acuminata in a patient with HIV disease.

Verrucous lesions in patients with human immunodeficiency virus (HIV) disease may be caused by viruses other than the human papillomavirus. We describe a 32-year-old HIV-positive black man who presented with a verrucous lesion of the intergluteal cleft that clinically resembled condyloma acuminata or verrucous carcinoma. Histopathological examination revealed the changes of herpes virus infection, and culture of the tissue confirmed the presence of herpes simplex virus. Human papillomavirus was not detected by in situ hybridization or the polymerase chain reaction. Significant regression of the lesion was seen after 6 weeks of treatment with oral acyclovir.

AIDS-Related Opportunistic Infections↗
PubMed1995

Cell membrane dynamics and insulin resistance in non-insulin-dependent diabetes mellitus.

Insulin resistance in non-insulin-dependent diabetes mellitus (NIDDM) could be related to changes in cell membrane properties. We measured insulin sensitivity and mononuclear leucocyte membrane fluidity by fluorescence polarisation in fifteen NIDDM patients and twenty-one normal subjects. Core-region anisotropy was significantly lower in leucocytes from diabetic subjects (mean 0.164 vs 0.174, p < 0.001). Insulin sensitivity was positively correlated with such anisotropy before and after acute in-vitro insulin treatment. There was no difference in superficial membrane anisotropy. This study suggests that altered membrane dynamics in NIDDM may contribute to insulin resistance.

Cell Membrane↗