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K Jacobson

Publications and source records attributed to K Jacobson.

At least 127 records · Page 7Linked to original sources
PubMed1987

Lateral diffusion of proteins in membranes.

Membrane protein lateral diffusion can be constrained in several ways: Diffusion can be slower than that predicted for a simple, fluid lipid bilayer; diffusion can be confined to certain regions within the total membrane; and diffusion may not be equally probable in all directions, i.e. it may be anisotropic. We know that protein diffusion is reduced by increasing concentrations of membrane proteins and by interactions of the diffusant with structure(s) peripheral to the membrane. The molecular nature of such peripheral constraints has been difficult to pinpoint, but attention is now being directed to the extracellular matrix in addition to the membrane-associated cytoskeleton. There are many proteins that are confined to lateral domains in differentiated, isolated cells and in cells organized into tissue. The mechanisms that maintain such inhomogeneous distributions should be elucidated in the next few years. Whether lateral diffusion of membrane proteins over distances of a few micrometers is usually isotropic or anisotropic will be ascertained in the near future using imaging methods combined with photobleaching.

Diffusion↗
PubMed1987

Benign positional vertigo: clinical and oculographic features in 240 cases.

We report the clinical and oculographic features in 240 patients with benign positional vertigo (BPV). In each case, after a rapid position change from the sitting to head-hanging position, a stereotyped torsional paroxysmal positional nystagmus was visually observed and recorded with electronystagmography (ENG). The mean age of onset was 54 years, with a range of 11 to 84 years. In slightly more than one-half of the cases (122/240) a likely diagnosis was determined. The most common identifiable causes were head trauma (17%) and viral neurolabyrinthitis (15%). Females outnumbered males approximately two to one in the idiopathic group. Abnormalities on bithermal caloric testing were found in 47% of patients. Only two patients, both with well-documented neurologic disorders, had central signs on ENG. Our data are consistent with a peripheral, posterior semicircular canal origin of BPV.

Adolescent↗
PubMed1986

Vertical visual-vestibular interaction in normal human subjects.

Previous studies have described asymmetrical vertical eye movements when normal human subjects were rotated about a vertical inter-aural axis (with head rolled 90 degrees). We measured vertical eye movements induced by visual, vestibular and visual-vestibular stimuli with a magnetic scleral search coil technique while 10 normal subjects sat upright in a chair designed to rotate about the horizontal inter-aural axis at frequencies and amplitudes of natural head movements. Asymmetries in the gain of upward and downward pursuit and fixation-suppression of the VOR were found in individual subjects. However, there was no significant difference (p greater than 0.05) between the mean gain of up and down slow eye movements induced by vestibular, visual or visual-vestibular stimulation in the group of normal subjects. Systematic up-down asymmetries in vertical eye movements previously observed with testing about the vertical inter-aural axis were probably due to bias introduced by otolith stimulation and/or electro-oculographic eyelid artifact.

Adult↗
PubMed1984

The translational mobility of substances within the cytoplasmic matrix.

The translational mobility of fluorescent-labeled molecules injected into the cytoplasm of living cells can be measured by the fluorescence recovery after photobleaching (FRAP) technique. In the fibroblast cytoplasm, the diffusion coefficients, D, of test macromolecules ranging in molecular weight from 12,000 to 440,000 are about 10(-8) cm2/sec and exhibit almost no dependence on molecular weight. FRAP experiments also showed that macromolecular diffusion within Sepharose beads having an effective pore size smaller than the "microtrabecular lattice" is only slightly retarded compared to buffer values--in contrast to the marked retardation measured in the cytoplasm. This leads to the conclusion that diffusion in the cytomatrix is dominated not by steric effects but rather by binding of the diffusing species to elements of the cytomatrix. These diffusion rates were difficult to modulate; cytochalasin, colchicine (except at 5 degrees C), and taxol treatments had little effect. The diffusion rates were not dependent on cellular energy metabolism. However, hypotonic treatment increased the D for bovine serum albumin by nearly 2-fold, whereas hypertonic treatment halved D. Withdrawing the free water from the cell by using 44% polyethylene glycol treatment stopped the translational mobility of the test molecules. A survey of the recent literature is presented, which shows that major differences in the cytomatrix of different cell types exist with respect to the translational diffusion of injected probes. Finally, the spectrum of cytoplasmic translational mobilities ranging from small molecules to organelles is discussed.

Apoferritins↗
PubMed1984

Relationship between lateral diffusion, collision frequency, and electron transfer of mitochondrial inner membrane oxidation-reduction components.

Fluorescence recovery after photobleaching was used to determine the diffusion coefficients of the oxidation-reduction (redox) components ubiquinone, complex III (cytochromes b-c1), cytochrome c, and complex IV (cytochrome oxidase) of the mitochondrial inner membrane. All redox components diffuse in two dimensions as common-pool electron carriers. Cytochrome c diffuses in two and three dimensions concomitantly, and its diffusion rate, unlike that of all other redox components, is modulated along with its activity by ionic strength. The diffusion coefficients established in this study reveal that the theoretical diffusion-controlled collision frequencies of all redox components are greater than their experimental maximum (uncoupled) turnover numbers. Since electron transport is slower than the theoretical limit set by the lateral diffusion of the redox components, ordered chains, assemblies, or aggregates of redox components are not necessary to account for electron transport. Rather, mitochondrial electron transport is diffusion coupled, consistent with a "random-collision model" for electron transport.

Animals↗
PubMed1984

Redistribution of a major cell surface glycoprotein during cell movement.

The distribution in living cells of an 80,000-dalton major cell surface glycoprotein of murine fibroblasts has been studied by use of monoclonal antibodies. The presence of the molecule throughout the plasma membrane and on the substrate attached surface of the cell was demonstrated by immunofluorescence. Cell growth kinetics were not altered and the cells remained motile in the presence of the antibody. The uniform distribution of the direct immunofluorescence stain persisted for long periods (greater than 100 h), which indicates that the fluorescent monoclonal antibodies may be used to trace antigen surface distribution during cell functions. In motile cells, but not G0 or confluent cells, the degree of fluorescent staining decreased toward the leading edge; this gradient increased markedly during the time that the antibody was bound to the cells. However, the gradation was not seen with the lipid probe, dihexadecylindocarbocyanine. The antigen was "patched" only by the application of a second antibody directed to the rat monoclonal antibody and the relationships of these patches to the underlying cytoskeleton were characterized.

Animals↗
PubMed1984

Lateral diffusion of an 80,000-dalton glycoprotein in the plasma membrane of murine fibroblasts: relationships to cell structure and function.

The lateral diffusion of an 80,000-dalton major cell surface glycoprotein of murine fibroblasts has been measured. This antigen, identified through the use of monoclonal antibodies, is an integral glycoprotein distributed through the plasma membrane as judged by immunofluorescence and immunoelectron microscopy (see preceding paper). Measurements of fluorescence recovery after photobleaching were performed on the antigen-antibody complex within the plasma membrane of C3H/10T1/2 and NIH/3T3 cells after labeling the monoclonal antibody with fluorescein. Measurements were performed as a function of temperature, for interphase, mitotic, and G0 C3H/10T1/2 cells. The mean lateral diffusion coefficients (D) for the antibody-protein complex in interphase cells were in the range of 0.7-3.5 X 10(-10) cm2/s between 9 degrees and 37 degrees C, while that for the lipid analog probe, dihexadecylindocarbocyanine was about two orders of magnitude greater. This comparison indicates that peripheral interactions other than bilayer fluidity limit the lateral mobility of the antigen. The mobile fraction of mitotic, G0, and interphase cells showed a monotonic increase with temperature with most of the antibody-antigen complexes being free to move about 25 degrees C. Semi-quantitative interpretations of both the slow glycoprotein diffusion and the immobile fraction are offered. Comparison of diffusion coefficients for cells in different phases of the cell cycle does not reveal striking differences. Mobile fractions for G0 cells at 25 degrees C or less are substantially lower than in interphase cells. In all cases, there was a remarkably broad range of the fluorescence recovery data between different cells, resulting in up to a 10-fold variation in diffusion coefficients, which is far greater than the precision limits of the experiment. Diffusion values and mobile fractions were generally well within a factor of two when measured at several arbitrary points on a single cell. The origins of this cellular heterogenity remain to be elucidated. Lateral mobility in cell fragments and specific regions of single cells was also examined. The glycoprotein was mobile in ventral surface cell fragments. Its mobility was not altered in regions of cell-cell underlapping. However, the diffusion coefficient was threefold higher near the leading edge of motile cells compared to the trailing region. This difference may reflect weaker coupling of the glycoprotein to the underlying cytoskeleton in the dynamic leading edge region.

Animals↗
PubMed1984

Reserpinization: effects on parotid gland function.

Chronic reserpinization of mice and rabbits affected parotid gland function; cholinergic and beta-adrenergic-stimulated amylase release were significantly reduced, and cyclic-AMP and cyclic-GMP levels were significantly elevated above control-stimulated levels. Amylase released by dibutyryl-c-AMP was also reduced, suggesting a defect in stimulus-secretion coupling subsequent to c-AMP formation.

Amylases↗
PubMed1983

Lateral diffusion in membranes.

Lateral diffusion measurements, using the photobleaching techniques, have provided unique and quantitative data on the random translational motions of proteins and lipids of membranes. Proper interpretation of this body of data can yield new insight into the structure of biomembranes. A comparative review of the lateral diffusion of membrane components in artificial lipid bilayers and of the same components in natural membranes is presented to demonstrate the effects of protein concentration and peripheral constraints on lateral mobility. Recent data on the effects of cell-substrate and cell-cell contact on lateral diffusion are reviewed. Finally, some experimental perspectives are offered in terms of emerging biophysical and biological technology.

Animals↗
PubMed1983

Lateral diffusion of wheat germ agglutinin-labeled glycoconjugates in the membrane of differentiating HL-60 and U-937 cells assessed with fluorescence recovery after photobleaching (FRAP).

The promyelocytic leukemia cell line HL-60 and the histiocytic cell line U-937 were grown in suspension culture. They were induced to differentiate during 5-d cultivation in the presence of dimethylsulfoxide (DMSO; 1.3% w/v) or phorbol-12-myristate-acetate (PMA; 10(-7) M), which yields granulocyte- and macrophage-like cells, respectively. Differentiation was evidenced by increased capacity to recognize and phagocytize IgG- or complement-coated yeast particles. Aliquots taken from the cultures with and without DMSO (or PMA) were spun down directly on glass microscope slides, washed, labeled with fluoresceinated wheat germ agglutinin (WGA), and directly examined at room temperature for the rate of fluorescence recovery after photobleaching (FRAP). It was found that cultivation of the HL-60 and the U-937 cells in the presence of DMSO, which yields granulocyte-like cells, reduced the average value of lateral diffusion coefficient D (X 10(10] from 1.72 +/- 0.13 cm2s-1 to 0.97 +/- 0.13 cm2s-1 and from 1.77 +/- 0.11 cm2s-1 to 0.82 +/- 0.13 cm2s-1, respectively. U-937 cells grown with PMA also showed a reduction of D(X 10(10] to 0.88 +/- 0.10 cm2s-1. There was a larger immobile fraction of fluorescence in the HL-60 cells than in the U-937 cells, viz., 70-80% compared to 10-50%. The total number of binding sites for WGA was not altered, but the surface density changed, since the HL-60 and the U-937 cells became smaller and larger, respectively, when grown in the presence of DMSO. It is concluded that differentiation reduces the average lateral mobility of the WGA-binding membrane component by a factor around 2.

Cell Differentiation↗
PubMed1982

Synergism between aminoglycosides and cephalosporins with antipseudomonal activity: interaction index and killing curve method.

Combinations of gentamicin with cefotaxime, moxalactam, and ceftazidime were tested against 43 bacterial strains, most of them blood isolates. With an interaction index of less than or equal to 0.5 as borderline, synergism was demonstrated against 30 to 40% of the strains by the fractional inhibitory concentration index and against 50 to 70% by the fractional bactericidal concentration index. The reproducibility of the index was within +/- 0.2 for two-thirds of 40 repetitive assays and within +/- 0.4 to 0.5 for all of these assays. Similar results were obtained when netilmicin was substituted for gentamicin. The killing curve system for studying antibiotic synergism was standardized to give results comparable to those obtained with the interaction index. This was achieved when one-half of a previously determined minimum bactericidal concentration was used for single drugs and the amount of antibiotic was at least halved again when drugs were used in combination. An initial bacterial concentration of 10(5) to 10(6) colony-forming units per ml is recommended. Given these conditions, synergism could be defined as a 2-log 10 or more decrease in viable count given by both drugs together, as compared with the more active of the pair after 24 h. Prediction of killing curve results could then be obtained with the fractional bactericidal concentration index. When cephalosporins and gentamicin were combined from the start, the beta-lactam antibiotics were less susceptible to inactivation, as demonstrated in time-killing assays. If one of the antibiotics were added after 24 h, synergism was not demonstrable. The results indicate that the new cephalosporins may be advantageously combined with aminoglycosides.

Aminoglycosides↗
PubMed1981

Use of lectins and polyethylene glycol for fusion of glycolipid-containing liposomes with eukaryotic cells.

Efficient fusion of phospholipid vesicles with monolayer cultures of eukaryotic cells was accomplished by attaching glycolipid-containing vesicles to the cell surface by using a lectin displaying binding for both the cell surface and the glycolipid, followed by treatment with polyethylene glycol. Fusion was inferred from the transfer of fluorescent lipid analog probes embedded in the vesicle membrane over the entire cell surface and of fluoresceinated proteins from the aqueous space of the vesicle to the cytoplasm of the cell. Fluorescence recovery after photobleaching showed that both the injected membrane and the cytoplasmic markers were mobile. Two different lectin--glycolipid combinations [Ricinus communis agglutinin I-lactosylcerebroside and concanavalin A-tetradecyl- (or hexadecyl-) maltobionamide] were used to promote attachment of lipid vesicles before polyethylene glycol-induced fusion with BG-9 human fibroblasts, NIL-8M2 hamster cells, or L-929 mouse cells. In the absence of lectin or polyethylene glycol, fusion was negligible. However, when both the lectin and the glycol were used, a dramatic increase in the transfer of both vesicle membrane and aqueous space markers from the liposomes to the cells occurred.

Animals↗