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Biomedical subjects

M L Johnson

Publications and source records attributed to M L Johnson.

At least 109 records · Page 6Linked to original sources
PubMed1994

Dystrophic dendrites induced in cultured Purkinje cells by exposure to vinblastine.

Organotypic cerebellar cultures were exposed to the mitotic spindle inhibitor, vinblastine, and examined by light and electron microscopy, and electrophysiologically. Purkinje cells in exposed cultures had stunted, varicose dendrites when observed in preparations reacted with antibody to nonphosphorylated neurofilament protein. Ultrastructurally, microtubules were selectively reduced in Purkinje cell dendrites, which contained disarrayed excess smooth endoplasmic reticulum, but no large accumulations of densely packed neurofilaments. Spontaneous cortical discharges were initially increased in vinblastine treated cultures and then ceased, at which time the cultures became unresponsive to electrical stimulation. The vinblastine-induced changes were attributed to impaired intracellular transport secondary to disruption of Purkinje cell dendritic microtubules.

Animals↗
PubMed1994

Leukocyte colony-stimulating factors. A review of associated neutrophilic dermatoses and vasculitides.

BACKGROUND: Hematopoietic colony-stimulating factors are a diverse group of cytokines now commercially available through recombinant technology. The colony-stimulating factors have proven utility in a wide spectrum of cytopenic states, and their use is now common-place. Unlike many cytokines, the colony-stimulating factors are usually well tolerated. We present a dramatic case of pyoderma gangrenosum arising during granulocyte colony-stimulating factor therapy. Additionally, the relevant literature regarding cutaneous complications of colony-stimulating factor therapy is summarized. OBSERVATIONS: Including our case, two reported patients developed pyoderma gangrenosum while under colony-stimulating factor therapy. Sweet's syndrome presented in an additional three patients, and necrotizing vasculitis was precipitated in three others. The eruptions consistently developed after 1 to 2 weeks of colony-stimulating factor therapy and were apparently unrelated to the underlying systemic illness. Although most reactions developed de novo, three were superimposed on a preexisting inflammatory process. CONCLUSIONS: Serious cutaneous adverse effects of colony-stimulating factors are distinctly rare but include neutrophilic dermatoses and necrotizing vasculitis. Upregulation of neutrophilic function and secondary release of cytokines may induce these complications. Early recognition and cessation of colony-stimulating factor therapy will limit the morbidity of these adverse events.

Adult↗
PubMed1994

Distribution of distances between the tryptophan and the N-terminal residue of melittin in its complex with calmodulin, troponin C, and phospholipids.

We used frequency-domain measurements of fluorescence resonance energy transfer to measure the distribution of distances between Trp-19 of melittin and a 1-dimethylamino-5-sulfonylnaphthalene (dansyl) residue on the N-terminal-alpha-amino group. Distance distributions were obtained for melittin free in solution and when complexed with calmodulin (CaM), troponin C (TnC), or palmitoyloleoyl-L-alpha-phosphatidylcholine (POPC) vesicles. A wide range of donor (Trp-19)-to-acceptor (dansyl) distances was found for free melittin, which is consistent with that expected for the random coil state, characterized by a Gaussian width (full width at half maxima) of 28.2 A. In contrast, narrow distance distributions were found for melittin complexed with CaM, 8.2 A, or with POPC vesicles, 4.9 A. A somewhat wider distribution was found for the melittin complex with TnC, 12.8 A, suggesting the presence of heterogeneity in the mode of binding between melittin and TnC. For all the complexes the mean Trp-19 to dansyl distance was near 20 A. This value is somewhat smaller than expected for the free alpha-helical state of melittin, suggesting that binding with CaM or TnC results in a modest decrease in the length of the melittin molecule.

Calmodulin↗
PubMed1994

Fluorescence lifetime imaging of intracellular calcium in COS cells using Quin-2.

We describe the first fluorescence lifetime images of cells. To demonstrate this new capability we measured intracellular images of Ca2+ in COS cells based on the Ca(2+)-dependent fluorescence lifetime of Quin-2. Apparent fluorescence lifetimes were measured by the phase-modulation method using a gain-modulated image intensifier and a slow-scan CCD camera. We describe methods to correct the images for photobleaching during acquisition of the data, and to correct for the position-dependent response of the image intensifier. The phase angle Quin-2 images were found to yield lower than expected Ca2+ concentrations, which appears to be the result of the formation of fluorescent photoproducts by Quin-2. Fluorescence lifetime imaging (FLIM) does not require wavelength-radiometric probes and appears to provide new opportunities for chemical imaging of cells.

Animals↗
PubMed1994

Analytical methods for evaluating episodic secretory activity within neuroendocrine axes.

We review here our recent analytical methods designed to: (a) detect abrupt increases and decreases in serially measured concentrations of hormones, substrates, or metabolites in body fluids (discrete peak detection); (b) carry out combined calculations of in vivo hormone secretion and metabolic clearance without the infusion of labeled compounds (deconvolution analysis); and (c) assess nonequilibrium concentrations of total, bound, and free hormones or effectors following the injection or secretion of finite amounts of one or more ligands into a closed compartment containing high-affinity transport or binding proteins. First, in relation to discrete peak detection, we illustrate the application of Cluster analysis to immunoradiometrically assayed growth hormone (GH) profiles collected in blood sampled every 30 s over night in healthy young men. Secondly, as examples of deconvolution analysis, both a waveform-independent and a waveform-specific methodology are presented, and their applications discussed (e.g., for episodic GH secretion). Thirdly, to illustrate nonequilibrium interactions between a single blood transporter protein and a hormone/ligand, we highlight the impact of the high-affinity GH binding protein in plasma on the nonsteady-state time course of GH secretion and removal. Collectively, these novel neuroendocrine tools permit a more demanding and quantitative analysis of the temporal regulation of hormone, substrate, or metabolite secretion, distribution, interconversion, irreversible metabolic removal, and association with one or more high- or low-affinity plasma binding proteins. Based upon these dynamic principles, the complex operation of neuroendocrine feedback axes in vivo can be defined and assessed quantitatively and relevant hypotheses of regulation formulated and tested specifically.

Animals↗
PubMed1994

Analysis of anisotropy decays in terms of correlation time distributions, measured by frequency-domain fluorometry.

We describe the theory and practical aspects of analyzing fluorescence anisotropy decays in terms of correlation times distributions. In our model the rotational motions of the fluorophores were described using Gaussian or Lorentzian distributions of the correlation times. The theory is presented both for time and frequency-domain measurements, although the simulations and measurements are focused on the frequency-domain measurements of the anisotropy decays. Analysis of simulated data is presented to illustrate the nature of the data and the resolution which can be expected with presently available frequency-domain measurements. Additionally, we describe experimental data for samples where one can reasonably expect a single exponential and/or discrete multi-exponential correlation time distributions, and for samples where the anisotropy decay might be expected to display a distribution of correlation times. These samples include small single tryptophan peptides in propylene glycol, the single tryptophan residue in S. Nuclease, and the single tryptophan residue in the native and partially unfolded states of ribonuclease T1.

Amino Acid Sequence↗
PubMed1994

Analysis of nonequilibrium dynamics of bound, free, and total plasma ligand concentrations over time following nonlinear secretory inputs: kinetics of two or more hormones pulsed into compartments containing multiple variable-affinity binding proteins.

Equations (1) through (8) provide a general mathematical model of combined pulsatile and basal effector molecule secretion, distribution, association, dissociation, and metabolic removal. Independent and interactive dynamics of multiple effector molecules and multiple distinct acceptor/transport proteins can be modeled explicity to test relevant hypotheses of ligand binding and clearance.

Carrier Proteins↗
PubMed1994

Testing pulse detection algorithms with simulations of episodically pulsatile substrate, metabolite, or hormone release.

Mathematical computer-assisted simulations of episodic hormone, substrate, or metabolite release can be accomplished using explicit algebra and high-speed microprocessors. Such simulations are useful to describe the behavior of single or multiple pulse generators, as well as the expected output of these systems. Simulated series are helpful in evaluating the sensitivity, specificity, positive accuracy, and negative accuracy of discrete peak detection methods, and in deconvolution analysis. Specifically, deconvolution analysis should recover the correct half-life, production rate, frequency, amplitude, mass, and duration of pulsatile hormone secretion, and it should accurately estimate concurrent basal secretion, if present. Finally, multiple pulse generators provide an interesting simulation model for testing random burst concordance, evaluating how the surgelike release of a hormone can be accomplished, and assessing the interactions among several control systems. Lastly, special problems remain in simulating neuroendocrine pulsatility, namely, the impact of multiple binding proteins (see Table 1, p. 392 in this volume), the effects of strong and/or correlated circadian variations in burst frequency or amplitude or basal secretion, the development of improved statements of error and experimental uncertainty in the data, and the description of various modes of basal secretion.

Activity Cycles↗
PubMed1994

Fluorescence lifetime imaging microscopy: homodyne technique using high-speed gated image intensifier.

In the previous sections we demonstrated imaging of intracellular Ca2+ using our approach to FLIM. What other analytes can be imaged using FLIM? We have now characterized the lifetime of a good number of ion indicators. Based on these studies we know that Cl- can be imaged using FLIM with probes such as SPQ or MQAE, pH can be imaged using resorufin and probes of the SNAFL and SNARF (Molecular Probes) series, and Mg2+ can be imaged using Magnesium Green, Mag-quin-2, or Mag-quin-1 (Molecular Probes). At present, the probe for K+, as PBFI, are just adequate as a lifetime probe, but it seems likely that newer probes for Na+ (Sodium Green) and K+ will be practical for effective imaging. Of course, imaging of oxygen is possible using a wide variety of fluorophores. It should be noted that a wide variety of substances and/or phenomena are known to alter decay times, acting as quenchers. These include the phenomena of resonance energy transfer, collisional quenching, temperature effects, and viscosity effects. Also, the FLIM method is not limited to microscopic objects but can be possibly used in remote imaging of any object. Hence, FLIM will allow the imaging of the chemical and physical properties of objects based on the effects of the local environment on the decay kinetics of fluorophores. The instrumentation for FLIM is presently complex and requires a moderately complex laser source, a gain-modulated image intensifier, and a slow-scan CCD camera. However, one can readily imagine the instrumentation becoming rather compact, and even all solid-state, owing to advances in laser and CCD technologies and, more importantly, advances in probe chemistry. To be specific, the dye laser shown in Fig. 1 may be replaced by a simpler UV laser, such as the 354 nm HeCd laser which has become available (Fig. 11). Intensity modulation of a continuous wave sources can be accomplished with acoustooptic modulators. The scientific slow-scan CCD cameras are presently rather expensive, but they are used in the present instrumentation because of their linearity and high dynamic range. However, the increasing use of CCD detectors suggest that even the scientific-grade CCD cameras will soon become less costly. Additionally, the frame rates of these detectors continue to increase in response to the need for faster imaging. Furthermore, the performance of the video CCD cameras is increasing, as seen by the introduction of 10-bit video analog-to-digital (A/D) converters.(ABSTRACT TRUNCATED AT 400 WORDS)

Aminoquinolines↗
PubMed1994

A method of developing and weighting explicit process of care criteria for quality assessment.

The use of explicit criteria to evaluate how well processes of care conform to accepted standards is a key method of quality assessment. Synthesizing four decades of literature, we devised an inexpensive, 6-step method of developing reliable, content-valid, explicit process criteria. This paper describes the method using a set of congestive heart failure criteria. In step 1 of the Criteria Development Method, criteria are derived from state-of-the-art clinical literature. In step 2, criteria are refined by expert panels. In this study, panelists refined the items by mail in a three-round Delphi process. In step 3, decisions about unit-or differential item weighting are made; we derived differential item weights from the panelists' third-round ratings. Step 4 consists of flagging items which may yield little information, i.e., consensus items of low import, and nonconsensus items. Numeric flags were computed using third-round median ratings and their interquartile ranges. Selection of a scoring method to summarize scores and communicate results is done in step 5. In step 6, chart reviewers are trained, inter-rater reliability is measured, and items with poor reliability are culled. This straightforward developmental method can be used to devise explicit process criteria for use in ambulatory or hospital settings and to evaluate care delivered by different types of providers. The method yields reliable criteria representing accepted standards of current clinical practice. This high content validity is a sine qua non for convergent and predictive validity, both of which must be demonstrated in empirical studies in which the criteria are compared against external yardsticks.

Delphi Technique↗
PubMed1994

Site-to-site diffusion in proteins as observed by energy transfer and frequency-domain fluorometry.

We report measurements of the site-to-site diffusion coefficients in proteins and model compounds, which were measured using time-dependent energy transfer and frequency-domain fluorometry. The possibility of measuring these diffusion coefficients were shown from simulations, which demonstrate that donor (D)-to-acceptor (A) diffusion alters the donor frequency response, and that this effect is observable in the presence of a distribution of donor-to-acceptor distances. For decay times typical of tryptophan fluorescence, the simulations indicate that D-A diffusion coefficients can be measured ranging from 10(-7) to 10(-5) cm2/s. This possibility was verified by studies of a methylene-chain linked D-A pair in solutions of varying viscosity. The D-A diffusion was also measured for two labeled peptides and two proteins, melittin and troponin I. In most cases we used global analysis of data sets obtained with varying amounts of collisional quenchers to vary the donor decay time. Unfolding of troponin I results in more rapid D-A diffusion, whereas for melittin more rapid diffusion was observed in the alpha-helical state but over a limited range of distances.

Diffusion↗
PubMed1994

Distance-dependent fluorescence quenching of tryptophan by acrylamide.

We used GHz frequency-domain fluorometry to investigate the time-dependent intensity decays of N-acetyl-L-trytophanamide (NATA) when collisionally quenched by acrylamide in propylene glycol at 20 degrees C. The intensity decays of NATA became increasingly heterogeneous in the presence of acrylamide. The NATA intensity decays were not consistent with the Collins-Kimball radiation boundary condition (RBC) model for quenching. The steady-state Stern-Volmer plots show significant upward curvature. At low temperature in vitrified propylene glycol (-60%), where translational diffusion cannot occur during the lifetime of the excited state, quenching of NATA by acrylamide was observed. The Smoluchowski and RBC quenching models do not predict any quenching in the absence of translational diffusion. Hence, these frequency-domain and steady-state data indicate a through-space quenching interaction between NATA and acrylamide. The rate for quenching of NATA by acrylamide appears to depend exponentially on the fluorophore-quencher separation distance. Comparison of the time-resolved and steady-state data provides a sensitive method to determine the distance dependence of the fluorophore-quencher interaction. The distance-dependent rate of quenching also explains the upward curvature of the Stern-Volmer plot, which is often observed for quenching by acrylamide. These results suggest that the distance-dependent quenching rates need to be considered in the interpretation of quenching data of proteins by acrylamide.

Acrylamide↗
PubMed1994

Validation of deconvolution analysis of LH secretion and half-life.

Deconvolution methods constitute a class of analytic tools to quantitate hormone secretion and/or clearance in vivo. Although mathematically rigorous, deconvolution techniques have assumed, rather than proven, validity. Accordingly, we tested the validity of deconvolution analysis on true-positive human, animal (sheep and monkey), and computer-simulated data using the luteinizing hormone (LH) pulse signal as a relevant paradigm. We found that multiparameter deconvolution analysis has high discriminative sensitivity (human data 91%, animal 81%, computer-stimulated 95%) and specificity (human 90%, animal 81%, computer-simulated 100%). Sensitivity was impaired by low secretory burst amplitude (< 0.1 IU.l-1.min-1), short interpulse interval (< 60 min), infrequent venous sampling (every 20-30 min), and high random experimental variation (e.g., noise > 15%). Specificity was hindered by noise. Deconvolution accurately characterized the unknown hormone half-life (r = +0.994) and production rate (r = +0.990). Interoperator reliability was high when statistically based criteria for secretory pulse detection were applied. We conclude that multiparameter deconvolution, within recognizable constraints, is a valid and reliable tool for in vivo investigation of hormone secretion and half-life.

Algorithms↗