Biomedical subjects

T Lin

Publications and source records attributed to T Lin.

At least 73 records · Page 4Linked to original sources

PubMed2000

Auditory-nerve-fiber responses to high-level clicks: interference patterns indicate that excitation is due to the combination of multiple drives.

There has been no systematic study of auditory-nerve-fiber (ANF) responses to high-level clicks despite the advantages of clicks in revealing the natural resonances of a system. Cat single ANFs were studied using clicks up to 120 dB pSPL. Peri-stimulus-time (PST) histograms of responses were corrected for refractory effects, and compound PST (cPST) histograms were formed from rarefaction- and condensation-click PSTs. At low levels the responses followed the classic picture with each cPST appearing to be from a single resonant system followed by low-pass filtering that reduces high-frequency synchrony. In fibers across all characteristic frequencies, there were significantly different patterns at high click levels including several nonclassic features and "phase reversals," i.e., a peak in the rarefaction-click PST at low levels was replaced at high levels by a peak at the same latency in the condensation-click PST. There were two separate regions of nonclassic features and phase reversals, which indicates that auditory-nerve fibers are excited by the combination at some stage in the cochlea of at least three excitation drives derived from the acoustic stimulus. These data support the interpretation that the cochlear partition vibrates in multiple resonant modes with each mode producing one excitation drive and that the mix of modes varies with sound level.

Acoustic Stimulation↗

PubMed2000

Structural fingerprinting: subgrouping of comoviruses by structural studies of red clover mottle virus to 2.4-A resolution and comparisons with other comoviruses.

Red clover mottle virus (RCMV) is a member of the comoviruses, a group of picornavirus-like plant viruses. The X-ray structure of RCMV strain S has been determined and refined to 2.4 A. The overall structure of RCMV is similar to that of two other comoviruses, Cowpea mosaic virus (CPMV) and Bean pod mottle virus (BPMV). The sequence of the coat proteins of RCMV strain O were modeled into the capsid structure of strain S without causing any distortion, confirming the close resemblance between the two strains. By comparing the RCMV structure with that of other comoviruses, a structural fingerprint at the N terminus of the small subunit was identified which allowed subgrouping of comoviruses into CPMV-like and BPMV-like viruses.

Amino Acid Sequence↗

PubMed2000

Fas and Fas ligand in gut and liver.

Apoptosis (programmed cell death) has been shown to play a major role in development and in the pathogenesis of numerous diseases. A principal mechanism of apoptosis is molecular interaction between surface molecules known as the "death receptors" and their ligands. Perhaps the best-studied death receptor and ligand system is the Fas/Fas ligand (FasL) system, in which FasL, a member of the tumor necrosis factor (TNF) family of death-inducing ligands, signals death through the death receptor Fas, thereby resulting in the apoptotic death of the cell. Numerous cells in the liver and gastrointestinal tract have been shown to express Fas/FasL, and there is a growing body of evidence that the Fas/FasL system plays a major role in the pathogenesis of many liver and gastrointestinal diseases, such as inflammatory bowel disease, graft vs. host disease, and hepatitis. Here we review the Fas/FasL system and the evidence that it is involved in the pathogenesis of liver and gastrointestinal diseases.

Animals↗

PubMed2000

Phenotypic variation of familial hypertrophic cardiomyopathy caused by the Phe(110)-->Ile mutation in cardiac troponin T.

Mutation of the cardiac troponin T (cTnT) gene is a genetic determinant of familial hypertrophic cardiomyopathy (HCM). A Japanese family of 14 individuals, including 6 with HCM, was subjected to genetic and clinical assessment. Five exons of the cTnT gene were sequenced in all family members. A heterozygous or homozygous T(340)-->A (Phe(110)-->Ile) mutation in exon 9 of the cTnT gene was detected in 11 subjects. Morphological and functional evaluation of the left and right ventricles by echocardiography revealed that 4 of 9 individuals heterozygous for the mutant allele exhibited HCM with moderate cardiac hypertrophy. Cardiac hypertrophy and other clinical features in the 2 subjects homozygous for the mutation were more severe than were those in heterozygous individuals with HCM. Thus, the clinical features of HCM due to the Phe(110)-->Ile mutation in the cTnT gene appear to be modified by a gene dosage effect.

Adolescent↗

PubMed2000

Expression and regulation of connexin43 in rat Leydig cells.

Gap junctions are intercellular protein channels which provide a pathway for the exchange of ions and small molecules. This exchange of materials allows metabolic coupling of cells. Gap junction channels are made up of connexins, integral membrane proteins encoded by a multigene family. Rat testes contain mRNAs for at least five different connexins: Cx26, Cx32, Cx33, Cx37 and Cx43. Immunocytochemical studies have shown that Cx43 assembles gap junctions between Leydig cells. The present study investigated the expression and regulation of the Cx43 gene in rat Leydig cells. Purified Leydig cells were obtained from 40- to 80-day-old Sprague-Dawley rats using a combination of arterial perfusion, collagenase digestion, centrifugal elutriation and Percoll gradient centrifugation. Leydig cells from 20- and 30-day-old rats were isolated without arterial perfusion or centrifugal elutriation. Cx43 mRNA was present in 20-day-old rat Leydig cells, reached a plateau at day 40, and remained at high levels in 65- and 80-day-old rat Leydig cells. To evaluate the regulation of Cx43 gene expression, Leydig cells were cultured overnight and then treated with human chorionic gonadotropin (hCG) for variable periods of time. Addition of hCG (10 ng/ml) increased cytochrome P450 side-chain cleavage and steroidogenic acute regulatory protein mRNA levels and testosterone formation. However, Cx43 mRNA levels were inhibited by hCG in a time- and dose-dependent manner. Cx43 mRNA levels decreased 27% as early as 2 h after the addition of hCG and decreased 60% by 24 h. Treatment of Leydig cells with 8-bromo-cAMP (0.1 mM) for 6 and 24 h also reduced Cx43 mRNA levels by 36 and 56% respectively. Primary cultured Leydig cells stained strongly positive with anti-Cx43 monoclonal antibody. Treatment with hCG for 24 h reduced Cx43 signals and caused Cx43 to redistribute to the periphery of the cells. To evaluate the regulation of Cx43 in vivo, rats were treated with hCG (300 ng i.p.) and testes were removed 24 h later. Frozen section of testes revealed that these interstitial cells stained positive for 3beta-hydroxysteroid dehydrogenase (3beta-HSD) by histochemical staining and were positive for Cx43 by immunofluorescence staining. The adjacent seminiferous tubules stained only weakly positive for Cx43. Twenty-four hours after hCG treatment, 3beta-HSD activity increased while Cx43 immunostaining of Leydig cells was reduced. In conclusion, gap junction channels of Leydig cells are regulated by hCG both in vivo and in vitro. hCG increased Leydig cell steroidogenesis and steroidogenic enzyme mRNA levels but caused a redistribution of Cx43.

3-Hydroxysteroid Dehydrogenases↗

PubMed2000

[Study on unsupervised classification in marshland of endemic area of Schistosomiasis Japonica using satellite TM image data].

OBJECTIVE: To categorize the vegetation of marshland in the endemic areas of Schistosomiasis Japonica using satellite thematic mapper (TM)data in Liupo Village, Anhui Province. METHODS: Data of three satellite TM hands, namely TM3, TM4 and TM5, were selected to be used in classification with principal component analysis. Then, satellite TM images were applied to false color composite and unsupervised classification with computer software to manage the images. Finally, the resulting clusters were identified and reclassified by site visits to categorize the land coverage and vegetation. RESULTS: Five classifications of land coverage were generated, including poplar forest, bulrush and marshland, all with snail habitants. Based on the survey in the spring of 1998, the overall live snail density and infested snail density in the study areas were 0.510/0.11 m2 and 0.007/0.11 m2, respectively. CONCLUSION: Unsupervised classification, which is a technique for the interpretation of remotely sensed imagery, can contribute to the classification of environment with snail habitants and ecological diseases and become a new method in epidemiological studies.

Animals↗

PubMed2000

[A new look at the mechanism of cholera endemicity caused by Vibrio cholerae biotype eltor].

OBJECTIVE: Cholera caused by Vibrio cholerae biotype eltor (EVC) is an endemic disease, subsiding in winter and reappearing in spring and summer. Investigating the state of EVC during the intermittent time is of crucial importance in controlling this disease. METHODS: Different factors mimicking the internal and external environmental conditions of the host, including human and fish bile, bacterial phages and antibiotics were used experimentally to induce variation in EVC. EVC variants were isolated from the stool of diarrhea patients and river water in old endemic areas during the winter. The variants obtained were tested with gene probe hybridization, DNA restriction enzyme mapping, immunoenzyme staining and animal passaging. RESULTS: Due to the loss of cell walls, 3 kinds of EVC variants were obtained during induction: the L-form variant, with a complete loss of cell walls; the nonagglutinating variants, with the loss of surface O-antigen; the phage-resistant variants, with the loss of phage receptors. Similar variants were found in field isolation. This variation was proved to be phenotypic, with no change in genetic material: it was reversible and appeared in a seasonal pattern, which coincided with the endemicity of this disease. Passage in animal enhanced this reversion. In compensation for the loss of cell walls, cell membranes were greatly thickened, increasing the ability of the variants to survive during the unfavorable winter conditions. CONCLUSIONS: EVC varied in a seasonal pattern, coincident with the endemicity of this disease. The compensatory thickening of the cell membranes protects the EVC variants to survive the winter.

Cholera↗

PubMed2000

[Determination of micro amounts of calcium and magnesium in saturated high purity sodium chloride solution by FAAS].

Micro amounts of calcium and magnesium in saturated high purity sodium chloride solution were determined by flame atomic absorption spectrometry after the preseparation of calcium and magnesium from matrix solution through ion-exchange resin column filled with model 401 chelate resin. The parameters and operating conditions of the preseparation of calcium and magnesium from matrix solution were studied by orthogonal optimization process. The relative standard deviations of this method were 6.5% and 5.5% for calcium and magnesium, respectively. The recoveries were 99% and 94% for calcium and magnesium, respectively.

Calcium↗

PubMed1999

The refined crystal structure of cowpea mosaic virus at 2.8 A resolution.

Comoviruses are a group of plant viruses in the picornavirus superfamily. The type member of comoviruses, cowpea mosaic virus (CPMV), was crystallized in the cubic space group I23, a = 317 A and the hexagonal space group P6(1)22, a = 451 A, c = 1038 A. Structures of three closely similar nucleoprotein particles were determined in the cubic form. The roughly 300-A capsid was similar to the picornavirus capsid displaying a pseudo T = 3 (P = 3) surface lattice. The three beta-sandwich domains adopt two orientations, one with the long axis radial and the other two with the long axes tangential in reference to the capsid sphere. T = 3 viruses display one or the other of these two orientations. The CPMV capsid was permeable to cesium ions, leading to a disturbance of the beta-annulus inside a channel-like structure, suggesting an ion channel. The hexagonal crystal form diffracted X rays to 3 A resolution, despite the large unit cell. The large ( approximately 200 A) solvent channels in the lattice allow exchange of CPMV cognate Fab fragments. As an initial step in the structure determination of the CPMV/Fab complex, the P6(1)22 crystal structure was solved by molecular replacement with the CPMV model determined in the cubic cell.

Amino Acid Sequence↗

PubMed1999

Steady-state kinetic characterization of RB69 DNA polymerase mutants that affect dNTP incorporation.

The function of six highly conserved residues (Arg482, Lys483, Lys486, Lys560, Asn564, and Tyr567) in the fingers domain of bacteriophage RB69 DNA polymerase (RB69 gp43) were analyzed by kinetic studies with mutants in which each of these residues was replaced with Ala. Our results suggest that Arg482, Lys486, Lys560, and Asn564 contact the incoming dNTP during the nucleotidyl transfer reaction as judged by variations in apparent Km and kcat values for dNTP incorporation by these mutants compared to those for the exonuclease deficient parental polymerase under steady-state conditions. On the basis of our studies, as well as on the basis of the crystal structure of RB69 gp43, we propose that a conformational change in the fingers domain, which presumably occurs prior to polymerization, brings the side chains of Arg482, Lys486, Lys560, and Asn564 into the vicinity of the primer-template terminus where they can contact the triphosphate moiety of the incoming dNTP. In particular, on the basis of structural studies reported for the "closed" forms of two other DNA polymerases and from the kinetic studies reported here, we suggest that (i) Lys560 and Asn564 contact the nonbonding oxygens of the alpha and beta phosphates, respectively, and (ii) both Arg482 and Lys486 contact the gamma phosphate oxygens of the incoming dNTP of RB69 gp43 prior to the nucleotidyl transfer reaction. We also found that Ala substitutions at each of these four RB69 gp43 sites could incorporate dGDP as a substrate, although with markedly reduced efficiency compared to that with dGTP. In contrast in the parental exo- background, the K483A and Y567A substituted enzymes could not use dGDP as a substrate for primer extension. These results, taken together, are consistent with the putative roles of the four conserved residues in RB69 gp43 as stated above.

Alanine↗

PubMed1999

Ca2+-induced inhibition of the cardiac Ca2+ channel depends on calmodulin.

Ca2+-induced inhibition of alpha1C voltage-gated Ca2+ channels is a physiologically important regulatory mechanism that shortens the mean open time of these otherwise long-lasting high-voltage-activated channels. The mechanism of action of Ca2+ has been a matter of some controversy, as previous studies have proposed the involvement of a putative Ca2+-binding EF hand in the C terminus of alpha1C and/or a sequence downstream from this EF-hand motif containing a putative calmodulin (CaM)-binding IQ motif. Previously, using site directed mutagenesis, we have shown that disruption of the EF-hand motif does not remove Ca2+ inhibition. We now show that the IQ motif binds CaM and that disruption of this binding activity prevents Ca2+ inhibition. We propose that Ca2+ entering through the voltage-gated pore binds to CaM and that the Ca/CaM complex is the mediator of Ca2+ inhibition.

Amino Acid Sequence↗

PubMed1999

Autonomic denervations influence ocular dimensions and intraocular pressure in chicks.

Choroidal thickness and axial eye length in the chick undergo day/night fluctuations that can also be modulated by visual experience. In the present study, we tested the effect of parasympathetic and sympathetic denervations on both day/night and image dependent changes in ocular dimensions. We also correlated such changes with fluctuations in intraocular pressure. Parasympathectomy influenced choroidal thickness and its day/night fluctuation, but had no effect on vision dependent choroidal thickness modulation. Parasympathectomy also influenced-to a lesser extent-axial length and reduced the axial growth response to form vision deprivation. Sympathectomy had little effect on ocular dimensions, but reduced the day/night differences in intraocular pressure. We conclude that (a) the parasympathetic nervous system influences both choroidal thickness and axial length and participates in the neural control mechanism leading to form deprivation myopia and, (b) the day/night fluctuations of choroidal thickness and axial length are unlikely to be explained by fluctuations in intraocular pressure. For the regulation of choroidal thickness, we hypothesize the existence of two independent mechanisms. One involves the parasympathetic nervous system; it influences the day/night choroidal thickness fluctuation. The other uses a separate pathway and is driven by visual input.

Animals↗

PubMed1999

Molecular confirmation of carriers for Lowe syndrome.

OBJECTIVE: To determine the sensitivity and specificity of ocular examination for the carrier state of Lowe syndrome in females known to be either carriers or noncarriers by direct DNA diagnosis. DESIGN: Nonrandomized cohort study. PARTICIPANTS: Thirty-one females at risk for carrying Lowe syndrome in 3 families. METHODS: Slit-lamp biomicroscopy after pupillary dilation was performed by a single observer (RAL) who was masked as to carrier status as determined by allele-specific detection of mutations in genomic DNA. RESULTS: Carrier assessment predetermined by slit-lamp biomicroscopic examination yielded only one false-negative in a young girl 5 years of age and no false-positives among 31 female members examined. CONCLUSIONS: Slit-lamp examination is a highly accurate and sensitive test for carrier detection in Lowe syndrome, particularly in women of reproductive age.

Adolescent↗

PubMed1999

The crystal structure of cricket paralysis virus: the first view of a new virus family.

Numerous small, RNA-containing insect viruses are currently classified as picornaviruses, or as 'picorna-like', since they superficially resemble the true picornaviruses. Considerable evidence now suggests that several of these viruses are members of a distinct family. We have determined the gene sequence of the capsid proteins and the 2.4 A resolution crystal structure of the cricket paralysis virus. While the genome sequence indicates that the insect picorna-like viruses represent a distinct lineage compared to true picornaviruses, the capsid structure demonstrates that the two groups are related. These viral genomes are, thus, best viewed as composed of exchangeable modules that have recombined.

Amino Acid Sequence↗

PubMed1999

Pseudomonas aeruginosa outer-membrane protein F epitopes are highly immunogenic in mice when expressed on a plant virus.

A synthetic peptide (peptide 10) representing a surface-exposed, linear B cell epitope from outer-membrane (OM) protein F of Pseudomonas aeruginosa was shown previously to afford protection in mice from P. aeruginosa infection. This peptide was expressed in tandem with the protein F peptide 18 on each of the two coat proteins of cowpea mosaic virus (CPMV). The chimaeric virus particles (CVPs) expressing the peptides on the S (small) coat protein (CPMV-PAE4) and L (large) coat protein (CPMV-PAE5) were used to immunize mice. Following subcutaneous immunization in Freund's and QuilA adjuvants, CPMV-PAE4 induced antibodies predominantly against peptide 18, whereas CPMV-PAE5 produced antibodies exclusively against peptide 10, indicating that the site of peptide expression on CPMV influences its immune recognition. The anti-peptide antibodies elicited by CPMV-PAE5 were predominantly of the IgG2a isotype, indicating a highly polarized TH1-type response. The peptide-specific IgG2a strongly recognized the whole F protein, but more importantly, recognized protein F in all seven Fisher-Devlin immunotypes of P. aeruginosa. Furthermore, the peptide-specific IgG2a in CVP/QS-21 adjuvant-immunized mice was shown to bind complement and to augment phagocytosis of P. aeruginosa by human neutrophils in vitro. The ability of CPMV-PAE5 to induce P. aeruginosa-specific opsonic IgG2a gives it potential for further development as a protective vaccine against P. aeruginosa.

Animals↗

PubMed1999

Effect of aging on gender differences in neural control of heart rate.

To clarify the influence of gender on sympathetic and parasympathetic control of heart rate in middle-aged subjects and on the subsequent aging process, heart rate variability (HRV) was studied in normal populations of women (n = 598) and men (n = 472) ranging in age from 40 to 79 yr. These groups were divided into eight age strata at 5-yr intervals and were clinically diagnosed as having no hypertension, hypotension, diabetic neuropathy, or cardiac arrhythmia. Frequency-domain analysis of short-term, stationary R-R intervals was performed, which reveals very-low-frequency power (VLF; 0.003-0.04 Hz), low-frequency power (LF; 0.04-0.15 Hz), high-frequency power (HF; 0.15-0.40 Hz), the ratio of LF to HF (LF/HF), and LF and HF power in normalized units (LF% and HF%, respectively). The distribution of variance, VLF, LF, HF, and LF/HF exhibited acute skewness, which was adjusted by natural logarithmic transformation. Women had higher HF in the age strata from 40 to 49 yr, whereas men had higher LF% and LF/HF between 40 and 59 yr. No disparity in HRV measurements was found between the sexes in age strata >/=60 yr. Although absolute measurements of HRV (variance, VLF, LF, and HF) decreased linearly with age, no significant change in relative measurements (LF/HF, LF%, and HF%), especially in men, was detected until age 60 yr. We conclude that middle-aged women and men have a more dominant parasympathetic and sympathetic regulation of heart rate, respectively. The gender-related difference in parasympathetic regulation diminishes after age 50 yr, whereas a significant time delay for the disappearance of sympathetic dominance occurs in men.

Adult↗

PubMed1999

Autospecific gammadelta thymocytes that escape negative selection find sanctuary in the intestine.

alphabeta or gammadelta thymocytes whose T-cell receptors (TCRs) recognize endogenously expressed antigens (Ag) are autospecific and, thus, potentially self-reactive. In the thymus, such T cells are eliminated during T-cell development through a process known as negative selection. As a model of negative selection of gammadelta T cells, we have used G8 gammadelta-T cell transgenic mice, which express a gammadelta TCR that recognizes the nonpolymorphic MHC class I TL(b) molecule. Here, we demonstrate that negative selection of autospecific gammadelta T cells is almost complete in the adult thymus but is markedly attenuated in the neonatal thymus. A consequence of this attenuated negative selection is that potentially self-reactive gammadelta thymocytes are allowed to escape negative selection, undergo extrathymic differentiation, and find sanctuary in the intestinal epithelium. Interestingly, the ability of these potentially self-reactive gammadelta T cells to find sanctuary requires both the intestinal epithelial environment and the extrathymic presence of the self-Ag. The implications of these findings on the development and persistence of autoreactive T cells in autoimmune disease are discussed.

Aging↗

PubMed1999

Position-dependent processing of peptides presented on the surface of cowpea mosaic virus.

The plant virus cowpea mosaic virus (CPMV) has been developed as an epitope-presentation system. Numerous epitopes have been expressed in the betaB-betaC loop of the CPMV small coat protein, all of which undergo a cleavage reaction between their two carboxy-terminal residues. Although many peptides presented in this manner give an authentic immune response, this was not the case for the NIm-1A epitope from human rhinovirus-14. Crystallography revealed significant differences between the structure of NIm-1A on CPMV compared with its native configuration. The 3D structure of C PMV expressing NIm-1A was used to design alterations to the context of the NIm-1A graft.

Amino Acid Sequence↗