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S Lee

Publications and source records attributed to S Lee.

At least 1,009 records · Page 56Linked to original sources
PubMed1994

Design and synthesis of amphipathic 3(10)-helical peptides and their interactions with phospholipid bilayers and ion channel formation.

It has been reported that a peptide corresponding to the S4 segment in sodium channel protein is able to form voltage-dependent cation-selective ion channels (Tosteson, M. T., Auld, D. S., and Tosteson, D. C. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 707-710). However, biological and other physical properties remain unexamined. In the present study, three peptides, H-(Ala-Arg-Leu)8-OH (ARL8), H-(Val-Arg-Leu)8-OH (VRL8), and H-(Leu-Arg-Leu)8-OH (LRL8) which were designed on the basis of the S4 segment and expected to form 3(10)-helix, were synthesized and examined with regard to conformational change by the interaction with membranes, membrane perturbation ability, ion channel formation, and antimicrobial activity. According to CD spectra, these peptides were found to form a 3(10)-helical structure in the presence of dipalmitoyl-DL-alpha-phosphatidylcholine/dipalmitoyl-DL-alpha- phosphatidylglycerol (3:1) liposomes. The experiment of the peptide-induced leakage of carboxyfluorescein from liposomes showed that all the peptides had a strong ability to perturb membranes. The peptides were able to form cation-selective ion channels in planar asolectin lipid bilayers. The conductances of the ion channels were small (approximately 2 picosiemens for VRL8 and LRL8 and approximately 23 picosiemens for ARL8), suggesting that the peptides produce narrow pores or wider pores with certain permeable barriers that are a portion of the whole channels. The differences in their conductances depend possibly on the sizes of the side chains of Ala, Val, and Leu residues. However, non of the peptides showed antimicrobial activity (minimum inhibitory concentrations, > 50 micrograms/ml). Here, we present the first evidence that the peptides can form 3(10)-helical structures with long chain lengths in a lipid bilayer environment.

Amino Acid Sequence↗
PubMed1994

Ion channel activity of a synthetic peptide with a primary structure corresponding to the presumed pore-forming region of the voltage dependent potassium channel.

A 26-mer peptide of which the sequence contains the presumed pore forming region of the Shaker K+ channel (H5 region) was chemically synthesized. The peptide was found to interact and penetrate lipid membranes based on the fluorescence of Trp residues of the peptide in the presence and absence of liposomes. The secondary structure and the ion channel forming ability of the peptide were measured by CD spectroscopy and by a planar bilayer technique, respectively. The secondary structure of the peptide was composed of a mixture of an alpha-helix, beta-sheet, beta-turn, and a random coil. The content of beta-sheet structure was increased by the presence of liposomes. In planar bilayers, the peptide formed anion-selective ion channels with a larger conductance than that of the native Shaker K+ channel. These results suggest that the H5 region of the Shaker K+ channel can penetrate into lipid bilayers and form ion channel structures by itself, but it requires other structural components to reproduce the native characteristics of the K+ channel.

Amino Acid Sequence↗
PubMed1994

Morphological adaptation to diet in platyrrhine primates.

Morphological features of the jaws and teeth are examined in eight species of platyrrhine monkeys that coexist in the Suriname rainforest. Z-scores calculated from geometric predictions for several features of the feeding apparatus thought to have some functional significance (e.g., tooth dimensions, jaw robusticity, leverage of primary jaw elevators) are compared to a profile of the naturalistic dietary behavior of these species (i.e., proportions of fruit mesocarp, seeds, leaves, and fauna eaten). Several features are found exclusively in those platyrrhines whose dietary preferences are the most limited. Such specializations appear to be associated with a particular protein source exploited by a species to supplement a largely frugivorous diet. Ateles paniscus, which feeds primarily on the mesocarp of ripe fruit, has an adaptive morphology that emphasizes broad incisors. Chiropotes satanas (and to a slightly lesser extent, Pithecia pithecia) is a frugivore/seed predator with large upper and lower canines and a robust mandible. The frugivore/folivore Alouatta seniculus has a relatively large total molar area and effective mandibular condyle height. In all four of these strictly vegetarian species, the leverage of the masseter muscle is greater than that of temporalis. Of the omnivorous species, Cebus apella and C. nigrivittatus exploit both fauna and seeds for protein and exhibit an array of many of the above features, such as large teeth and thick mandibles. Saimiri sciureus, not particularly known for seed predation, departs from Cebus in having less robust canines and a more gracile mandible. All three cebid omnivores have a temporalis with greater leverage than the masseter, indicating a requirement for resisting anteriorly directed forces, for example, using the jaws for vigorous foraging. The lack of any enlarged features, other than incisors, in the omnivorous Saguinus midas may be attributable to the functional constraints of small body size. Because the small size of the gape limits the size of the food parcel ingested, a requirement to enlarge other dentomandibular structures for trituration is alleviated.

Adaptation, Physiological↗
PubMed1994

Murine strain variation in the natural killer cell and proliferative responses to the immunostimulatory compound 7-allyl-8-oxoguanosine: role of cytokines.

7-Allyl-8-oxoguanosine (loxoribine) is a di-substituted guanine ribonucleoside which has been shown previously to enhance murine NK activity, B lymphocyte proliferation, and antibody synthesis. In this study we examined the relationship among enhancement of NK activity, proliferation, and cytokine synthesis in the responses of different strains of mice to loxoribine to provide insight into the role of cytokines in these biological activities. The NK response of mice was enhanced both in vitro and in vivo in all strains tested with the exception of the NK-deficient beige (BgBg) mouse. However, there was a marked difference in the degree of NK enhancement noted in other inbred strains, with C3H and CBA mice producing the highest responses, C57BL/6, BALB/c, and DBA/2 strains giving intermediate responses, and SJL mice manifesting low responses. Striking enhancement of NK cell activity was seen in SCID mice. A somewhat different effect was seen in humans. Loxoribine treatment enhanced both the NK and LAK activity of cells from individuals with low and high spontaneous NK activity. The degree of enhancement was similar for both groups, and thus the general hierarchy of NK activity among different donors was maintained. There was less interstrain variation in the murine proliferative response to loxoribine although nude (NuNu) mice showed the highest activity and SJL mice produced substantially lower responses than other strains. All strains produced IL-6, TNF alpha, IFN-alpha/beta, and IFN-gamma when spleen cells were cultured for 48 hr with loxoribine. Interstrain variability of cytokine synthesis displayed no consistent pattern from one cytokine to another, and all failed to correlate with interstrain variability of NK cell activity or B lymphocyte proliferation. When anti-cytokine antibodies were tested for the ability to block the immunostimulatory effects of loxoribine, only anti-IFN-alpha/beta and, to a lesser degree, anti-IFN-beta, partially inhibited NK activation. Similarly, only anti-IFN alpha/beta antibodies partially blocked the proliferative response to loxoribine. In both cases, reconstitution of the responses was achieved by adding back IFN-alpha/beta to cultures containing antibodies against IFN-alpha/beta. These data suggest that, although several cytokines are produced in response to loxoribine, only IFN-alpha and IFN-beta are directly involved in the NK activation and proliferative responses. The pattern of strain variation appears to be reflective of variation in NK cell responsiveness to IFN-alpha/beta.

Adjuvants, Immunologic↗
PubMed1994

Interleukin-1 and transforming growth factor-alpha: synergistic stimulation of metalloproteinases, PGE2, and proliferation in human fibroblasts.

Wound healing and other inflammatory processes are driven by a complex series of interactions among cells, the extracellular matrix, and secreted products of various cell types. Cytokines, such as interleukin-1 and transforming growth factor-alpha, are present at wound sites and contribute to the proinflammatory milieu of these sites. In the present study, we have investigated the effect of these cytokines, individually and in concert, on fibroblast expression of matrix metalloproteinases, which contribute to extracellular matrix remodeling, and of prostaglandin E2, which alters vascular tone and permeability. The metalloproteinases, procollagenase (matrix metalloproteinase-1) and prostromelysin (matrix metalloproteinase-3), are induced by exposure of dermal fibroblasts to interleukin-1, not stimulated by transforming growth factor-alpha, but are synergistically induced by the combination of cytokines. The 92-kDa type IV procollagenase (matrix metalloproteinase-9, progelatinase B), is also stimulated in synergistic fashion. Prostaglandin E2 is induced in rheumatoid synovial fibroblasts by interleukin-1 beta, not altered by transforming growth factor-alpha, and is synergistically released by the combination of the two cytokines. Fibroblast proliferation, which is also a component of normal wound healing, is also synergistically stimulated by the action of the two cytokines in concert. These results indicate that interleukin-1 beta and transforming growth factor-alpha synergize to elicit a number of phenotypic responses in fibroblasts which are relevant to normal wound healing and chronic inflammation.

Arthritis, Rheumatoid↗
PubMed1994

Stimulatory effect of cocaine on ACTH secretion: role of the hypothalamus.

The administration of cocaine to rats causes the release of adrenocorticotropin hormone (ACTH). The observation that immunoneutralization of endogenous corticotropin-releasing factor (CRF) significantly blunts this response has suggested the importance of CRF-dependent pathways in this response. As the paraventricular nucleus (PVN) of the hypothalamus represents a major source of the CRF delivered to the pituitary, the present studies investigated the role of this hypothalamic nucleus in mediating cocaine-induced ACTH secretion. We first observed that one single iv injection of 5 mg cocaine/kg, or two sequential sc injections of 40 mg cocaine/kg, caused a measurable increase in steady-state levels of CRF mRNA. Bilateral lesions of the PVN significantly (P < 0.01) decreased the ability of cocaine to release ACTH measured 15 min later. Though we failed to measure any changes in the levels of the mRNA encoding for vasopressin (VP) following either regimen of drug administration, we noted that rats in which the magnocellular portion of the PVN (which contains VP perikarya) was spared, showed a normal ACTH response to cocaine. We therefore studied the possibility that VP might regulate the activity of the corticotrophs in response to cocaine. However, prior iv injection of polyclonal antibodies against VP did not measurably alter cocaine-induced ACTH secretion, while in the same experiment, immunoneutralization of endogenous CRF completely blocked the stimulatory action of cocaine. Taken together, these results show that CRF of PVN origin represents the major modulator of ACTH released in response to cocaine, while VP does not appear to play an important role.

Adrenocorticotropic Hormone↗
PubMed1994

Interaction between alcohol and interleukin-1 beta on ACTH secretion and the expression of immediate early genes in the hypothalamus.

We have observed that alcohol does not alter adrenocorticotropin (ACTH) released in response to the iv injection of interleukin-1 beta (IL-1 beta). In contrast, prior (-30 to -90 min) administration of moderate doses of alcohol (0.5-2.0 g/kg) significantly blunts ACTH secretion following the intracerebroventricular (icv) injection of the cytokine. We explored two possible mechanisms responsible for this phenomenon: Corticosteroid feedback and alcohol-induced inhibition of hypothalamic neuronal activation (measured through changes in c-fos and NGFI-B mRNA levels). Increasing plasma corticosterone levels by exposing rats to mild electroshocks or injecting them with corticosterone did not alter ACTH released by rats administered with IL-1 beta into the brain ventricles. Alcohol, which by itself did not stimulate c-fos or NGFI-B mRNA levels in the paraventricular nucleus of the hypothalamus, significantly blunted the ability of icv IL-1 beta to increase the expression of these immediate early genes. We conclude that the inhibitory influence exerted by prior alcohol treatment on ACTH released by icv administered IL-1 beta may reflect an interference with the stimulatory influence of the cytokine on hypothalamic neurons involved in the activation of the hypothalamic-pituitary-adrenal axis.

Adrenocorticotropic Hormone↗
PubMed1994

NADH and NAD modulates Ca(2+)-activated K+ channels in small pulmonary arterial smooth muscle cells of the rabbit.

We have investigated the effect of NADH and NAD on the gating of large conductance Ca(2+)-activated K(KCa) channels in arterial smooth muscle cells isolated from small pulmonary artery (outer diameter < 300 microns) and ear artery, using the patch clamp technique. In the inside-out configuration, intracellularly applied 2 mM NADH inhibited the activity of KCa channels in pulmonary arterial smooth muscle cells, while it had no significant effect on ear arterial smooth muscle cells. On the other hand, 2 mM NAD increased the opening of KCa channels in pulmonary arterial smooth muscle cells. The effects of another intracellular redox couple, glutathione(GSH) and glutathione disulfide(GSSG) were also dependent on their redox potentials. GSH(5 mM) inhibited KCa channels activity, while GSSG(5 mM) increased the activity of pulmonary arterial smooth muscle cells. It could be concluded that the modulation of KCa channels by intracellular redox state contributes, at least in part, to the hypoxic suppression of outward current in pulmonary arterial smooth muscle cells.

Animals↗
PubMed1994

12-Deoxyphorbol-13-O-phenylacetate 20 acetate [an agonist of protein kinase C beta 1 (PKC beta 1)] induces DNA synthesis, interleukin-2 (IL-2) production, IL-2 receptor alpha-chain (CD25) and beta-chain (CD122) expression, and translocation of PKC beta isozyme in human peripheral blood lymphocytes: evidence for a role of PKC beta 1 in human T cell activation.

To determine a role of protein kinase C (PKC) isozymes in lymphocyte activation, human peripheral blood mononuclear cells were activated with 12-deoxyphorbol-13-O-phenylacetate (dPP; an agonist of both calcium-dependent and calcium-independent PKC isozymes), thymeleatoxin (TX; an activator of calcium-dependent PKC alpha, beta, and gamma), and 12-deoxyphorbol-13-O-phenylacetate 20 acetate (dPPA; an activator of PKC beta 1 isozyme) and examined for DNA synthesis, lymphocyte proliferation, interleukin-2 (IL-2) production, expression of IL-2 receptor alpha and beta chains on CD3+, CD4+, and CD8+ T lymphocytes and CD20+ B lymphocytes, and translocation of PKC beta isozyme from cytosol to membrane fraction. The results show that dPPA activates lymphocytes by inducing the above changes in a manner analogous to that of dPP, TX, and phorbol myristate acetate. These data suggest that PKC beta 1 is involved in the activation of human peripheral blood T and B lymphocytes.

DNA↗
PubMed1994

Changes in glutamate receptor and proenkephalin gene expression after kindled seizures.

Changes in gene expression after kindled seizures were examined using microdissection of discrete brain areas and Northern and slot blot analyses. Experimental animals were kindled with either of two protocols: (1) a paradigm in which 50 Hz/10 s stimulus trains were delivered every 30 min through hippocampal electrodes (12 stimulations every other day for 4 days) and (2) a traditional approach in which 50 Hz/10 s stimulus trains were given to the hippocampus three times daily for 16 days. Rats were sacrificed 24 h or 30 days after the last kindled seizure. We first examined the possibility that kindling may affect transcription of mRNA for neurotransmitter receptors. We found significant decreases (22-58%) in AMPA/kainate activated glutamate receptor mRNAs (GluR1, -2, -3 mRNAs) in hippocampus, amygdala/entorhinal cortex and in frontoparietal cortex 24 h but not 30 days after rapidly kindled seizures. However, changes in GABA receptor alpha 1, alpha 2, alpha 4 or beta 1 mRNAs were not observed in any brain region 30 days after traditional kindling or 24 h after rapidly kindled seizures. In addition, we tested whether changes in the expression of proenkephalin could be detected after kindling. We found significant increases (1.7-10 fold) in proenkephalin mRNA in the frontoparietal cortex, hippocampus and in the amygdala/entorhinal cortex 24 h but not 30 days after rapidly kindled seizures. Our findings suggest that changes in glutamate receptor and proenkephalin gene expression are robust, acute sequelae to kindled seizures and may be involved in kindling.

Amygdala↗
PubMed1994

Induction of c-fos and CRF mRNA by MK-801 in the parvocellular paraventricular nucleus of the rat hypothalamus.

The non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine maleate (MK-801) stimulates the secretion of adrenocorticotropin hormone (ACTH). As corticotropin-releasing factor (CRF) represents the primary modulator of this secretion, we tested the hypothesis that the ability of MK-801 to activate the hypothalamic-pituitary-adrenal (HPA) axis was modulated through actions at the hypothalamic level that modulate the secretion of CRF. Induction of the immediate-early gene c-fos, as well as of CRF mRNA within the paraventricular nucleus (PVN) of the rat hypothalamus, was examined following the intraperitoneally administration of MK-801 (1 mg/kg). MK-801 markedly increased the expression of Fos-like protein in parvocellular nerve cells of the PVN within 60 min of systemic treatment, and double labeling immunocytochemistry indicated that Fos was primarily localized in CRF-containing neurons of the PVN. MK-801 also significantly increased CRF biosynthesis as detected by in situ hybridization, thus suggesting that c-fos could be involved in the regulation of CRF genes. Taken together, these results suggest that MK-801 stimulates the rat HPA axis probably through the neuronal gene expression of PVN CRF. The significance of these data is discussed in terms of hypothalamic NMDA receptor blockade and subsequent transcriptional regulation of CRF by immediate-early genes.

Animals↗
PubMed1994

Nonrandom allelic variation in the regulatory complex of HLA class I genes.

Recently, we have demonstrated that the HLA class I regulatory complex (CRC) is conserved in a locus-specific manner with limited allelic variation. In this study, we have analyzed the CRC sequences of the alleles that showed variation from a total of 22 well-characterized, HLA-homozygous B-LCLs, using PCR amplification of genomic DNA and direct sequencing. We compared the sequences of these alleles with their respective locus consensus sequence at kappa B1, kappa B2, the IRS, the putative NRE, and the HLA counterpart of the H-2RII region, the R x R beta-binding site. The palindromic kappa B1 sequence, an active enhancer, was found to be conserved in all HLA-A and -B alleles and in one HLA-C allele. The sequences of the kappa B2 site showed locus-specific divergence with almost no allelic variation. The IRS is strictly locus specific and HLA-B and -C have identical sequences in this region. Variation in the putative NRE sequence and RII-kappa B2 junctional sequence was apparently generated by gene conversion between B and C loci. Each locus had two sequence patterns at the putative RII site. Overall, sequence analysis of variant alleles demonstrated that there is limited variation in a nonrandom fashion. These results may provide a structural basis for locus and allele-specific modulation of these genes.

Alleles↗
PubMed1994

MRI in cylindrical coordinates.

We obtained the nuclear density distribution of a disk in 25 ms by using an one-dimensional (1D) imaging technique in the cylindrical coordinates. A magnetic field gradient coil implementing the cylindrical coordinates in MRI was devised by simply changing the direction of current flow at the central part of a solenoid for easy construction. The current distributions, which give the maximum field gradient in the radial direction and the ratio of the field gradient in the radial direction to that in the axial direction, were found numerically as a function of the solenoid length and the number of turns of reverse current at the center. The ratio of the radial gradient and the axial gradient of the designed coil is large enough to produce an undistorted 1D image in the radial direction of a slice perpendicular to the axis. The reverse current prevents the image from being shifted in a spectrum. The gradient coil gives images which agree with theoretical expectations within 5% error. Our result is applicable to the imaging of dynamic objects with cylindrical symmetry which do not change substantially during the order of milliseconds.

Humans↗
PubMed1994

Aminotransferase catalysis applied to the synthesis of a PAF antagonist.

(R)-alpha-Methyl-3-pyridinebutanamine (5) was required as a key intermediate for production of the PAF antagonist [(R)-(E,E)-5-(4-methoxyphenyl)-N-1- methyl-4-(3-pyridinyl)butyl-2,4-decadienamide (1). A method meeting the requirements of technical simplicity and economic viability was developed using an aminotransferase ex. B. megaterium to catalyze a kinetic resolution of racemic alpha-methyl-3-pyridinebutanamine (3). 5-(3-Pyridinyl)-2-pentanone (4) produced from the (S)-enantiomer, with co-generation of alanine, is recycled by catalytic reductive amination.

Bacillus megaterium↗
PubMed1994

Studies on lipid membranes by two-dimensional Fourier transform ESR: Enhancement of resolution to ordering and dynamics.

The first two-dimensional Fourier-transform electron spin resonance (2D-FT-ESR) studies of nitroxide-labeled lipids in membrane vesicles are reported. The considerable enhancement this experiment provides for extracting rotational and translational diffusion rates, as well as orientational ordering parameters by means of ESR spectroscopy, is demonstrated. The 2D spectral analysis is achieved using theoretical simulations that are fit to experiments by an efficient and automated nonlinear least squares approach. These methods are applied to dispersions of 1-palmitoyl-2oleoyl-sn-glycerophosphatidylcholine (POPC) model membranes utilizing spin labels 1-palmitoyl-2-(16-doxyl stearoyl) phosphatidylcholine and the 3-doxyl derivative of cholestan-3-one (CSL). Generally favorable agreement is obtained between the results obtained by 2D-FT-ESR on vesicles with the previous results on similar systems studied by continuous wave (cw) ESR on aligned samples. The precision in determining the dynamic and ordering parameters is significantly better for 2D-FT-ESR, even though the cw ESR spectra from membrane vesicles are resolved more poorly than those from well aligned samples. Some small differences in results by the two methods are discussed in terms of limitations of the methods and/or theoretical models, as well as possible differences between dynamic molecular structure in vesicles versus aligned membranes. An interesting observation with CSL/POPC, that the apparent homogeneous linewidths seem to increase in "real time," is tentatively attributed to the effects of slow director fluctuations in the membrane vesicles.

Computer Simulation↗