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Biomedical subjects

W W Webb

Publications and source records attributed to W W Webb.

At least 127 records · Page 7Linked to original sources
PubMed1977

Lateral transport of a lipid probe and labeled proteins on a cell membrane.

Diffusion coefficients (D) of a lipid probe and labeled proteins on L-6 myoblast membranes have been measured giving D(protein) approximately 2 X 10(-10) square centimeter per second and D (lipid probe) approximately 9 X 10(-9) square centimeter per second. Some of the membrane proteins are immobile, but the lipid probe diffuses freely over macroscopic distances. Cytochalasin B slows protein but not lipid probe diffusion.

Azides↗
PubMed1977

Lateral diffusion in planar lipid bilayers.

Direct measurements by fluorescence correlation spectroscopy of lateral diffusion coefficients of fluorescent lipid analogs in lipid bilaryer membranes indicate self-diffusion coefficients D greater than 10(-7) square centimeters per second for various lipid systems above their reported transition temperatures. Cholesterol in egg lecithin at mole ratio of 1 : 2 reduces D by about twofold, while retained hydrocarbon solvent can increase it by two- to threefold.

Cholesterol↗
PubMed1977

Receptor diffusion on cell surfaces modulated by locally bound concanavalin A.

In order to test the anchorage modulation hypothesis, the fluorescence photobleaching recovery method was used to measure the global inhibition of cell surface receptor mobility induced in 3T3 mouse fibroblasts by local binding of platelets labeled with concanavalin A (Con A). By measuring the diffusion of antibody-labeled cell surface receptors at various points on the cell surface, two states, immobile and mobile, were distinguished in the receptor population. Bound Con A-platelets, occupying between 4% and 30% of the cell surface, decreased the diffusion coefficient of the mobile population by a factor of 6. The magnitude of this effect was independent of distance from the sites of the bound Con A-platelets, demonstrating the propagated and nonlocal properties of the modulation effect. The immobile fraction of the population was not changed by Con A-platelet binding. Modulation of the diffusion constant of mobile receptors was partially reversed by treatment with microtubule-disrupting agents such as Colcemid and Vinca alkaloids. High doses of soluble Con A induced even higher levels of modulation than Con A-platelets, but reversal by microtubule-disrupting drugs was observed. These experiments provide additional support for the anchorage modulation hypothesis and provide a measure of the nature and degree of mobility at the molecular level. They also put important constraints on the hypothesized interactions among submembranous components (microtubules and microfilaments) of surface modulating assemblies.

Antigen-Antibody Complex↗
PubMed1977

Mobility and distribution of a cell surface glycoprotein and its interaction with other membrane components.

Fluorescence photobleaching recovery and immunofluorescence methods have been used to study the lateral mobility and topographical distribution of a major cell surface glycoprotein (CSP). Both endogenous CSP and fluorescent-labeled exogenous CSP bind to the cell surface in a fibrillar pattern and are immobile on the experimental time scale. Azide, vinblastine, and cytochalasin B do not alter the immobility and cell surface distribution of the CSP molecules. Therefore, oxidative phosphorylation and the cytoskeleton do not seem to be responsible for the properties of the bound glycoprotein. The presence of immobile CSP fibrils does not, however, impede the diffusion of a lipid probe, a ganglioside analogue, or various surface antigens. Therefore, the fibrils apparently do not form a "barrier" across the lipid phase of the plasma membrane. In contrast, concanavalin A binds to CSP and is largely immobile in regions rich in CSP. The presence of immobile concanavalin A receptors in areas or on cells lacking CSP indicates that other types of immobile concanavalin A receptors also exist.CSP does not bind to lipid bilayers composed of phosphatidylcholine or oxidized cholesterol. It does bind to dextran-coated bilayers as a diffuse distribution of mobile molecules that can patch after addition of antibodies to CSP. The latter result suggests that CSP molecules do not interact strongly with other CSP molecules under these conditions. Exogenous CSP binds to regions on the cell surface that already bear CSP. In view of the apparent weakness of CSP-CSP interactions on the lipid bilayer, it seems possible that the assembly of CSP fibrils is nucleated by cell surface components in addition to CSP.

Antigens↗
PubMed1976

Jejunoileal bypass procedures in morbid obesity: preoperative psychological findings.

Seventy patients who averaged 155% overweight and requested jejunoileal bypass surgery as a treatment intervention for morbid obesity were studied preoperatively for prominent psychological characteristics. By use of standard personality tests and a structured psychiatric interview, it was found that 89% were judged to be psychologically favorable risks for the operation. Most frequently the diagnostic opinion was of a mild personality disorder.

Adult↗
PubMed1976

Mobility measurement by analysis of fluorescence photobleaching recovery kinetics.

Fluorescence photobleaching recovery (FPR) denotes a method for measuring two-dimensional lateral mobility of fluorescent particles, for example, the motion of fluorescently labeled molecules in approximately 10 mum2 regions of a single cell surface. A small spot on the fluorescent surface is photobleached by a brief exposure to an intense focused laser beam, and the subsequent recovery of the fluorescence is monitored by the same, but attenuated, laser beam. Recovery occurs by replenishment of intact fluorophore in the bleached spot by lateral transport from the surrounding surface. We present the theoretical basis and some practical guidelines for simple, rigorous analysis of FPR experiments. Information obtainable from FPR experiments includes: (a) identification of transport process type, i.e. the admixture of random diffusion and uniform directed flow; (b) determination of the absolute mobility coefficient, i.e. the diffusion constant and/or flow velocity; and (c) the fraction of total fluorophore which is mobile. To illustrate the experimental method and to verify the theory for diffusion, we describe some model experiments on aqueous solutions of rhodamine 6G.

Biological Transport↗
PubMed1976

Dynamics of fluorescence marker concentration as a probe of mobility.

We have developed an effective experimental system for the characterization of molecular and structural mobility. It incorporates a modified fluorescence microscope geometry and a variety of analytical techniques to measure effective diffusion coefficients ranging over almost six orders of magnitude, from less than 10(-11) cm2/s to greater than 10(-6) cm2/s. Two principal techniques, fluorescence correlation spectroscopy (FCS) and fluorescence photobleaching recovery (FPR), are employed. In the FPR technique, translational transport rates are measured by monitoring the evolution of a spatial inhomogeneity of fluorescence that is produced photochemically in a microscopic volume by a short burst of intense laser radiation. In contrast, FCS uses laser-induced fluorescence to probe the spontaneous concentration fluctuations in microscopic sample volumes. The kinetics are analyzed by computing time-correlation functions of the stochastic fluctuations of the measured fluorescence intensity. The optical system and digital photocount correlator designed around a dedicated minicomputer are described and discussed. The general power of these techniques is demonstrated with examples from studies conducted on bulk solutions, lipid bilayer membranes, and mammalian cell plasma membranes.

Biological Transport↗
PubMed1976

Lateral motion of fluorescently labeled acetylcholine receptors in membranes of developing muscle fibers.

We have made direct, quantitative measurements of the lateral motion and age-dependent distribution of acetylcholine receptors (AChR) on the surface of rat myotubes in primary culture. AChR were fluorescently marked with tetramethylrhodamine-labeled alpha-bungarotoxin and AChR lateral motion was measured by the fluoresence photobleaching recovery technique. We found two coexisting distinct classes of AChR: (i) mobile, uniformly distributed AChR that appear on all myotubes shortly after fusion from myoblasts; and (ii) immobile, dense, highly granular AChR in patches of 10-60 mum size that appear shortly after fusion and disappear after myotubes have become extensively interconnected. In addition, evidence of turnover of AChR labeled with tetramethylrhodamine-alpha-bungarotoxin is seen in the gradual internalization of surface fluorescence within 36 hr after labeling. The relevance of these results to an understanding of the membrane dynamics and localization of muscle AChR is discussed.

Age Factors↗
PubMed1976

Lateral transport on cell membranes: mobility of concanavalin A receptors on myoblasts.

We report measurements of the lateral mobility of fluorescent labeled concanavalin A receptor complexes on the plasma membrane of cultured myoblasts of rat. Transport rates were measured by observing the recovery of fluorescence in a small region of the cell surface initially photobleached irreversibly by an intense, focused laser light pulse. Under different conditions we measured effective diffusion coefficients of the receptor complexes in the range 8 x 10(-12) less than D less than 3 x 10(-11) cm2/sec which is two orders of magnitude lower than we found for a fluorescent lipid probe, D approximately (8 +/- 3) x 10(-9) cm2/sec. This large difference and the presence of apparently immobile concanavalin A receptors suggests that factors beyond the fluoidity of the phospholipid bilayer membrane matrix control the rate of lateral transport of the complexes. Effective mobilities of the complexes decrease with increases in the valence, dose, and occupation time of the lectin on the membrane. These properties imply an aggregation of the lectin-receptor complexes. Mobilities are not influenced by azide, colchicine or preincubation at low temperature. Cytochalasin B and low temperatures, during the time of measurement, decrease the lateral transport rate.

Azides↗
PubMed1976

Psychological adaptation to jejunoileal bypass for morbid obesity.

Psychological adaptation to jejunoileal bypass procedures in 34 morbidly obese patients was evaluated preoperatively and followed postoperatively for an average of 23 months. Preoperative emotional disturbances were mainly those of mild personality disorders with passive-aggressive, passive-dependent, and emotionally immature traits. Following discharge from the hospital, nine patients (or 24 per cent) developed psychiatric difficulties, characterized by either increased neurotic symptoms and interpersonal problems, or the emergence of psychosis. Male patients and those with the greatest weight loss were statistically more likely to have psychiatric complications. The remaining patients expressed satisfaction with the operation, noted relief from the burden of dieting, experienced less excitement associated with eating, and felt more self-confident and hopeful.

Adaptation, Psychological↗
PubMed1976

Measurement of lateral transport on cell surfaces.

This paper describes the principles and recent applications of two new methods for measuring rates of macroscopic lateral transport of fluorescent-labeled particles on the surface of individual cells. Both methods are based on microfluorimetric measurements of fluorescence intensity from a small open region (greater than or equal to 1 micronm radius) on the cell surface. Transport rates are measured from the rates at which the measured fluorescence intensity changes due to entrance or departure of fluorophores from the region. One method, "Fluorescence Photobleach Recovery" (FPR), uses a brief intense pulse of light to create an initial concentration gradient over the spot by irreversible photochemical destruction of fluorophores. The rate of fluorescence recovery due to transport of unbleached fluorophores into the observation region is the primary experimental datum. The other method, "Fluorescence Correlation Spectroscopy" (FCS), is based on a statistical analysis of spontaneous fluctuations of numbers of fluorophores in the observation region and does not require a perturbation to generate an initial concentration gradient. FCS is mainly useful to measure relatively fast processes (D greater than or equal to 10(-9) cm 2/sec) in stable systems; FPR can be used to measure both slow and fast transport in less stable systems. Using both FCS and FPR, the diffusion coefficient of a fluorescent lipid probe in rat myoblast plasma membranes was measured to be D = (9 +/- 4) X 10(-9) cm2/sec over a range of at least 4 micronm. FPR was used to measure the lateral mobility of the fluorescent labeled lectin concanavalin A complexed to myoblast plasma membrane "receptors." A fraction of the complexes were immobile on the time scale of the experiment (D less than 8 x 10(-12) cm2/sec). The remainder of the complexes had effective diffusion coefficients far smaller than expected from the measurements on the lipid probe (8 x 10(-12) less than or equal to D less than or equal to 3.3 x 10(-11) cm2/sec). Moreover the mobility depended on the valence, dose, and time of occupancy of the lectin on the membrane, suggesting that an aggregation of complexes was occurring during the experiment. Cytochalasin B decreased the mobility of complexes, suggesting an influence of microfilaments on the transport process. Neither azide nor colchine affected measured transport rates. These results indicate the operation of constraints on the mobility of the lectin-receptor complexes beyond that exerted by the viscous resistance of the lipid bilayer membrane matrix. The two types of interactions revealed by our current experiments - interactions of the complexes with microfilaments and with each other (aggregation) - seem insufficient to account entirely for the low observed mobility.

Animals↗
PubMed1974

Auditory membrane vibrations: measurements at sub-angstrom levels by optical heterodyne spectroscopy.

We describe an optical technique for measurement of mechanical vibrations in the auditory organs of living animals. The technique uses light scattered from the vibrating structure and offers several new advantages. Better than 1 angstrom sensitivity, 10 micrometers spatial resolution, and > 70 decibels dynamic range are achieved. Illustrative measurements of the mechanical response of the tympanic membrane of crickets (Gryllidae) are reported.

Animals↗