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Results: 31 to 35 of 35

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A general model of microcirculatory blood flow effects in gradient sensitized MRI.
Kennan RP, Gao JH, Zhong J, Gore JC
(1994) Med Phys 21: 539-45
MeSH Terms: Biophysical Phenomena, Biophysics, Blood Flow Velocity, Capillaries, Computer Simulation, Humans, Magnetic Resonance Imaging, Microcirculation, Models, Cardiovascular
Show Abstract · Added December 10, 2013
A general expression is derived for the NMR signal from a fluid undergoing random directional flow such as encountered within the microcirculation. The dependence of the echo amplitude on flow velocity, sample morphology, and experimental parameters are described in terms of a temporal velocity autocorrelation function. The width of the correlation function determines whether the flow can properly be described as diffusive. Comparison is made between the velocity autocorrelation method outlined here and the IVIM model for tissue perfusion. Conditions for the validity of the latter approach for extracting physiologic information from apparent diffusion measurements are discussed. The approach outlined leads to a more robust measure of microcirculatory blood velocity from NMR measurements.
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9 MeSH Terms
Inactivation of L-type Ca channels in embryonic chick ventricle cells: dependence on the cytoskeletal agents colchicine and taxol.
Galli A, DeFelice LJ
(1994) Biophys J 67: 2296-304
MeSH Terms: Animals, Biophysical Phenomena, Biophysics, Calcium Channels, Chick Embryo, Colchicine, Cytoskeleton, Heart Ventricles, In Vitro Techniques, Kinetics, Models, Biological, Paclitaxel
Show Abstract · Added February 19, 2015
This article shows that colchicine and taxol strongly influence the kinetics of L-type Ca channels in intact cardiac cells, and it suggests a mechanism for this action. It is known that colchicine disassociates microtubules into tubulin, and that taxol stabilizes microtubules. We have found that colchicine increases the probability that Ca channels are in the closed state and that taxol increases the probability they are in the open state. Moreover, taxol lengthens the mean open time of Ca channels. In this regard, taxol is similar to Bay-K 8644; however, Bay K works on inside-out patches, but taxol does not. Neither colchicine nor taxol alters the number of Ca channels in a patch. We have quantified these results as follows. It is known that L-type channels in embryonic chick heart ventricle cells have voltage- and current-dependent inactivation. In 10 mM Ba, channel conductance is linear in the range -10 to 20 mV. The conductance is 12 +/- 1 pS, and the extrapolated reversal potential is 42 +/- 2 mV (n = 3). In cell-attached patches, inactivation depends on the number of channels. One channel (holding at -80 mV and stepping to 0 mV for 500 ms) shows virtually no inactivation. However, three channels inactivate with a time constant of 360 +/- 20 ms (n = 6). In similar patches, colchicine (80 microM for 15 min) decreases the inactivation time constant to 162 +/- 33 ms (n = 4) and taxol (50 microM for 10 min) virtually abolishes inactivation (time constant 812 +/- 265 ms (n = 4)). We suggest that colchicine and taxol affect Ca channels through their action on the cytoskeleton, which in turn regulates the effective concentration of inactivating ions near the mouths of channels. An alternate explanation is that free tubulin interacts directly with Ca channels.
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12 MeSH Terms
Measurement of rotational dynamics by the simultaneous nonlinear analysis of optical and EPR data.
Hustedt EJ, Cobb CE, Beth AH, Beechem JM
(1993) Biophys J 64: 614-21
MeSH Terms: Biophysical Phenomena, Biophysics, Data Interpretation, Statistical, Diffusion, Electron Spin Resonance Spectroscopy, Eosine Yellowish-(YS), Fluorescence Polarization, Fluorescent Dyes, Models, Chemical, Motion, Proteins, Rotation, Serum Albumin, Bovine, Spin Labels
Show Abstract · Added January 20, 2015
In the preceding companion article in this issue, an optical dye and a nitroxide radical were combined in a new dual function probe, 5-SLE. In this report, it is demonstrated that time-resolved optical anisotropy and electron paramagnetic resonance (EPR) data can be combined in a single analysis to measure rotational dynamics. Rigid-limit and rotational diffusion models for simulating nitroxide EPR data have been incorporated into a general non-linear least-squares procedure based on the Marquardt-Levenberg algorithm. Simultaneous fits to simulated time-resolved fluorescence anisotropy and linear EPR data, together with simultaneous fits to experimental time-resolved phosphorescence anisotropy decays and saturation transfer EPR (ST-EPR) spectra of 5-SLE noncovalently bound to bovine serum albumin (BSA) have been performed. These results demonstrate that data from optical and EPR experiments can be combined and globally fit to a single dynamic model.
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14 MeSH Terms
Protein rotational dynamics investigated with a dual EPR/optical molecular probe. Spin-labeled eosin.
Cobb CE, Hustedt EJ, Beechem JM, Beth AH
(1993) Biophys J 64: 605-13
MeSH Terms: Biophysical Phenomena, Biophysics, Electron Spin Resonance Spectroscopy, Eosine Yellowish-(YS), Fluorescence Polarization, Fluorescent Dyes, Luminescence, Molecular Probes, Motion, Proteins, Rotation, Serum Albumin, Bovine, Solutions, Spin Labels
Show Abstract · Added January 20, 2015
An acyl spin-label derivative of 5-aminoeosin (5-SLE) was chemically synthesized and employed in studies of rotational dynamics of the free probe and of the probe when bound noncovalently to bovine serum albumin using the spectroscopic techniques of fluorescence anisotropy decay and electron paramagnetic resonance (EPR) and their long-lifetime counterparts phosphorescence anisotropy decay and saturation transfer EPR. Previous work (Beth, A. H., Cobb, C. E., and J. M. Beechem, 1992. Synthesis and characterization of a combined fluorescence, phosphorescence, and electron paramagnetic resonance probe. Society of Photo-Optical Instrumentation Engineers. Time-Resolved Laser Spectroscopy III. 504-512) has shown that the spin-label moiety only slightly altered the fluorescence and phosphorescence lifetimes and quantum yields of 5-SLE when compared with 5-SLE whose nitroxide had been reduced with ascorbate and with the diamagnetic homolog 5-acetyleosin. In the present work, we have utilized time-resolved fluorescence anisotropy decay and linear EPR spectroscopies to observe and quantitate the psec motions of 5-SLE in solution and the nsec motions of the 5-SLE-bovine serum albumin complex. Time-resolved phosphorescence anisotropy decay and saturation transfer EPR studies have been carried out to observe and quantitate the microseconds motions of the 5-SLE-albumin complex in glycerol/buffer solutions of varying viscosity. These latter studies have enabled a rigorous comparison of rotational correlation times obtained from these complementary techniques to be made with a single probe. The studies described demonstrate that it is possible to employ a single molecular probe to carry out the full range of fluorescence, phosphorescence, EPR, and saturation transfer EPR studies. It is anticipated that "dual" molecular probes of this general type will significantly enhance capabilities for extracting dynamics and structural information from macromolecules and their functional assemblies.
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14 MeSH Terms
Gramicidins A, B, and C form structurally equivalent ion channels.
Sawyer DB, Williams LP, Whaley WL, Koeppe RE, Andersen OS
(1990) Biophys J 58: 1207-12
MeSH Terms: 1,2-Dipalmitoylphosphatidylcholine, Amino Acid Sequence, Biophysical Phenomena, Biophysics, Circular Dichroism, Gramicidin, Ion Channels, Lipid Bilayers, Lysophosphatidylcholines, Molecular Sequence Data, Molecular Structure
Show Abstract · Added March 5, 2014
The membrane structure of the naturally occurring gramicidins A, B, and C was investigated using circular dichroism (CD) spectroscopy and single-channel recording techniques. All three gramicidins form channels with fairly similar properties (Bamberg, E., K. Noda, E. Gross, and P. Läuger. 1976. Biochim. Biophys. Acta. 419:223-228.). When incorporated into lysophosphatidylcholine micelles, however, the CD spectrum of gramicidin B is different from that of gramicidin A or C (cf. Prasad, K. U., T. L. Trapane, D. Busath, G. Szabo, and D. W. Urry. 1983. Int. J. Pept. Protein Res. 22:341-347.). The structural identity of the channels formed by gramicidin B has, therefore, been uncertain. We find that when gramicidins A and B are incorporated into dipalmitoylphosphatidylcholine vesicles, their CD spectra are fairly similar, suggesting that the two channel structures could be similar. In planar bilayers, gramicidins A, B, and C all form hybrid channels with each other. The properties of the hybrid channels are intermediate to those of the symmetric channels, and the appearance rates of the hybrid channels (relative to the symmetric channels) corresponds to what would be predicted if all three gramicidin molecules were to form structurally equivalent channels. These results allow us to interpret the different behavior of channels formed by the three gramicidins solely on the basis of the amino acid substitution at position 11.
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11 MeSH Terms