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Biomedical subjects

L Liu

Publications and source records attributed to L Liu.

At least 919 records · Page 51Linked to original sources
PubMed1996

Cardiac transient outward potassium current: a pulse chemistry model of frequency-dependent properties.

Recent voltage-clamp studies of isolated myocytes have demonstrated widespread occurrence of a transient outward current (I(to)) carried by potassium ions. In the canine ventricle, this current is well developed in epicardial cells but not in endocardial cells. The resultant spatial dispersion of refractoriness is potentially proarrhythmic and may be amplified by channel blockade. The inactivation and recovery time constants of this channel are in excess of several hundred milliseconds, and consequently channel availability is frequency dependent at physiological stimulation rates. When the time constants associated with transitions between different channel conformations are rapid relative to drug binding kinetics, the interactions between drugs and an ion channel can be approximated by a sequence of first-order reactions, in which binding occurs in pulses in response to pulse train stimulation (pulse chemistry). When channel conformation transition time constants do not meet this constraint, analytical characterizations of the drug-channel interaction must then be modified to reflect the channel time-dependent properties. Here we report that the rate and steady-state amount of frequency-dependent inactivation of I(to) are consistent with a generalization of the channel blockade model: channel availability is reduced in a pulsatile exponential pattern as the stimulation frequency is increased, and the rate of reduction is a linear function of the pulse train depolarizing and recovery intervals. I(to) was reduced in the presence of quinidine. After accounting for the use-dependent availability of I(to) channels, we found little evidence of an additional use-dependent component of block after exposure to quinidine, suggesting that quinidine reacts with both open and closed I(to) channels as though the binding site is continuously accessible. The model provides a useful tool for assessing drug-channel interactions when the reaction cannot be continuously monitored.

Animals↗
PubMed1996

Regional and functional factors determining induction and maintenance of atrial fibrillation in dogs.

The present study was designed to determine the factors governing the ability of premature beats at various atrial sites to initiate atrial fibrillation (AF) and the determinants of the duration of AF in dogs at 1-10 Hz. The site of atrial extrasystoles determined their ability to induce AF. Regional differences in AF inducibility were due to differences in local refractoriness. Premature beats initiated AF by blocking in regions of greater refractoriness, causing macroreentrant activation with subsequent disorganization producing fibrillation. The atrial refractory period and wavelength during rapid 1:1 atrial pacing were weak predictors of AF duration (r = 0.24 and 0.23, respectively), which depended strongly on variability in regional refractoriness measured by the standard deviation in local refractory periods (r = 0.80, P < 0.001) and on the heterogeneity of activation during AF (r = 0.74, P < 0.001). Thus, premature beats cause AF by initiating a single macroreentrant cycle that degenerates into multiple wavefronts, regional refractoriness is the primary determinant of AF induction by premature beats, and variability in refractoriness may be an important determinant of the ability of AF to sustain itself.

Animals↗
PubMed1996

Involvement of annexin II in exocytosis of lamellar bodies from alveolar epithelial type II cells.

Annexins are a family of Ca(2+)- and phospholipid-binding proteins that have been implicated in exocytosis. In the present study, we investigated the participation of selected annexins in exocytosis of lamellar bodies by examining their liposome aggregation property and ability to reconstitute surfactant secretion from permeabilized rat lung alveolar type II cells. Annexins I, II, III, and VI were demonstrated in type II cells by immunoblot analysis, but annexin IV and V were not found. Annexins I-IV mediated liposome aggregation in the presence of 1 mM Ca2+. However, only annexin II tetramer had aggregation activity at 10 microM Ca2+. Annexins V and VI had negligible aggregation activity at any Ca2+ concentrations (up to 1 mM Ca2+). To study reconstitution of secretion by annexins, isolated type II cells were permeabilized with 40 microM beta-escin. Under these conditions, the permeabilized cells released approximately 30-40% lactic acid dehydrogenase into the medium. An underestimated fraction of cellular annexin content was lost during permeabilization. However, lamellar bodies in the permeabilized type II cells stained appropriately with the fluorescent dyes Nile red and quinacrine, indicating that they were intact. These permeabilized cells were secretion competent, since phosphatidylcholine (PC) secretion was stimulated by 0.2-1.0 microM Ca2+. Addition of an exogenous annexin mixture enhanced PC secretion from the permeabilized type II cells with maximal stimulation at 0.5 microM Ca2+. Of six purified annexins (I-VI) tested for their ability to reconstitute secretion from permeabilized cells, only annexin II was effective. Our results suggest that annexin II is not necessary for exocytosis of lamellar bodies.

Animals↗
PubMed1996

Hydroxylation of salicylate in lungs of Fischer 344 rats: effects of aging and ozone exposure.

The formation of 2,3-dihydroxybenzoic acid (DHBA) from salicylate was measured in the lungs and plasma to assay for the .OH in juvenile (2 mo), adult (9 mo), and senescent (24 mo) Fischer 344 male rats exposed to clean air, 1 part/million (ppm) ozone, or 2 ppm ozone for 2 h. Similar rates of distribution of salicylic acid in plasma and to the lungs were observed among air control animals of all age groups. Levels of 2,3-DHBA were about twice as high in the lungs of air control senescent rats compared with juvenile and adult rats (P < 0.05). Exposure to ozone resulted in 1.5- to 2-fold elevation of 2,3-DHBA in lungs and plasma of all age groups (P < 0.05), whereas levels of 2,5-DHBA were not changed significantly. There was no effect of age on the magnitude of 2,3-DHBA increase in the lungs or plasma after ozone exposure. The postulated source of .OH is chemical reduction of H2O2, which could be generated from increased age-dependent endogenous oxidant production or the age-independent reaction of ozone or macrophage-derived oxidants with the surfactant lining.

Aging↗
PubMed1996

RT-PCR microlocalization of mRNAs for calbindin D28k and vitamin D receptor in the murine nephron.

The spatial relationship between vitamin D receptor (VDR) and calbindin D28k [calcium binding protein D28k (CaBP-D28k)] gene expression within the murine kidney was studied by localizing their mRNAs in discrete nephron structures using reverse transcription-polymerase chain reaction (RT-PCR). Primers for beta-actin mRNA were used as a control for the presence of tissue during RT-PCR for CaBP-D28k mRNA. mRNA for CaBP-D28k was found only in distal convoluted tubules (DCTs), connecting tubules (CNTs), and cortical collecting ducts (CCDs). In contrast, VDR mRNA was detected in glomeruli, S2 proximal convoluted tubules, cortical thick ascending limbs of Henle's loop, DCTs, CNTs, and initial CCDs. The presence of both VDR and CaBP-D28k mRNA in DCTs, CNTs, and CCDs is consistent with the hypothesis that cacitriol acts via the VDR to stimulate CaBP-D28k synthesis. Conversely, the presence of VDR mRNA in other parts of the nephron suggests that calcitriol has genomically mediated actions within the kidney in addition to stimulation of CaBP-D28k synthesis.

Actins↗
PubMed1996

Capsaicin-induced currents with distinct desensitization and Ca2+ dependence in rat trigeminal ganglion cells.

1. Whole cell patch-clamp records from cultured rat trigeminal ganglion cells having soma diameters ranging from 20 to 50 microM revealed that capsaicin activated two inward currents and an outward current. At -60 mV, the inward currents could be distinguished by their different peak times, which were 4.2 +/- 3.1 and 41.4 +/- 16.4 (SD) s. 2. Cells with the smallest soma diameters had the largest current densities. 3. The more rapidly activating current had a linear current-voltage relation and a reversal potential near 0 mV. 4. The more slowly activating current is not a Ca(2+)-activated Cl- current. 5. The peak of the rapid current (Ip)-capsaicin concentration (C) relationship was characterized by Ip/Ipmax = [1 + (C/Kd)n]-1, where n = 1.2 and the dissociation constant (Kd) = 0.68 microM. 6. The rapidly activating current was heterogeneous in regards to both its rate of activation and extent of desensitization. In cells bathed in buffer containing calcium and held at -60 mV, most of the capsaicin-activated currents desensitized. Removal of extracellular Ca2+ could reduce, eliminate, or have no effect on desensitization. 7. At positive holding potentials the currents very slowly desensitized, even in the presence of Ca2+. 8. Repeated 30-s applications of 1 microM capsaicin separated by 0.5, 2.5, and 5.5 min all induced tachyphylaxis. Tachyphylaxis decreased exponentially until the current remained approximately constant. Decreasing the time between capsaicin applications increased the extent of tachyphylaxis, whereas elimination of extracellular Ca2+ markedly reduced tachyphylaxis.

Animals↗
PubMed1996

Similarities and differences in the currents activated by capsaicin, piperine, and zingerone in rat trigeminal ganglion cells.

1. Capsaicin, piperine, and zingerone are natural pungent-tasting compounds found in chili pepper, black pepper, and ginger, respectively. These structurally related compounds evoke many of the same physiological responses, but at comparable concentrations capsaicin produces complete tachyphylaxis, piperine produces partial tachyphylaxis, and zingerone can either induce or not induce tachyphylaxis. Whole cell patch-clamp studies were performed on rat trigeminal ganglion cells to determine the similarities and differences between these three pungent compounds. 2. Capsaicin (1 microM) activated a variety of inward currents having peak times ranging from 2 to 46 s that desensitized to various extents ranging from 0 to 100%. The inward currents activated by zingerone (30 mM) had peak times of approximately 2 s and all currents exhibited marked desensitization. The inward currents activated by piperine (100 microM) had peak times of approximately 25 s and all exhibited a small desensitization. 3. Piperine- and zingerone-induced currents were found only in cells that could be activated by capsaicin. 4. Capsazepine (10 microM), an established antagonist of capsaicin-induced currents, inhibited the currents evoked by piperine and zingerone, suggesting that all three compounds activate vanilloid receptors. 5. Dose-response relationships for capsaicin, piperine, and zingerone obtained at a holding potential of -60 mV had threshold and apparent dissociation constants of 0.1 and 0.68 microM, 3 and 35 microM, and 1 and 15 mM, respectively. These values were consistent with those previously obtained in behavioral studies. 6. After seven 30-s applications of 1 microM capsaicin or 100 microM piperine (in a buffer with 2 mM Ca2+), each interspersed with 2-min, 50-s washes, the peak currents were inhibited by approximately 60 and 40%, respectively. In contrast, 30 mM zingerone failed to evoke a current after six applications. After complete tachyphylaxis produced by 30 mM zingerone, 1 microM capsaicin failed to evoke a current, suggesting that these two compounds cross desensitize. 7. The similar physiological responses produced by these three compounds can be rationalized by their binding to receptors and activating currents that can all be inhibited by capsazepine. Their different physiological responses evoked by these compounds can be rationalized, in part, by their very different activation and desensitization kinetics, and perhaps by the existence of different subtypes of vanilloid receptors.

Alkaloids↗
PubMed1996

Cul-de-sac hypernasality test with pattern recognition of LPC indices.

Acoustic differences between samples of [i], [u], and [a] uttered in nose-open and nose-obstructed condition were studied in 6 women with isolated cleft palate and pathological nasalance scores and 9 healthy women with normal nasalance scores. The speech samples were depicted by 14-component vocal tract area feature vectors obtained by linear prediction and the differences between the samples were studied with a self-organized feature map. Each location on the map corresponds to a certain signal pattern, neighboring locations to similar patterns. The group of healthy subjects differed from the patients for vowels [i] and [u] but not for [a]. In the patients the nose obstruction induced a significant change in the location of these vowel samples on the map. In healthy subjects no such changes were detected. The results agreed with perceived differences between the subjects.

Adolescent↗
PubMed1996

Transmigration of human neutrophils across airway epithelial cell monolayers is preferentially in the physiologic basolateral-to-apical direction.

To study the mechanisms involved in the movement of neutrophils from the blood stream into the lung airways, we investigated human neutrophil transmigration across a monolayer of human airway epithelial cells, both in the apical-to-basolateral direction and in the more physiologic basolateral-to-apical direction. Migration of human neutrophils across monolayers of human airway epithelial H292 cell-line cells and primary bronchial epithelial cells occured most efficiently in the basolateral-to-apical direction, both after the addition of chemoattractants to resting epithelial cells and across interleukin-1beta (IL-1beta)-stimulated epithelial cells. Blocking studies with monoclonal antibodies revealed that the migration of neutrophils was mediated by the CR3 adhesion molecule (CD11b/CD18) on the neutrophils. IL-1beta-treated epithelial cells caused neutrophil movement via the secretion of chemoattractants. The most potent chemoattractant released by the epithelial cells was found to be IL-8, because the IL-1beta-induced migration was inhibited for 75 +/- 10% by the addition of an antibody against IL-8. After apical stimulation of the epithelial cells with an optimal concentration of IL-1beta, 27 +/- 4 ng/ml IL-8 was found in the supernatant at the apical side of epithelial cells. Platelet-activating factor (PAF) synthesis by the epithelial cells did not play a role in neutrophil transmigration, as was demonstrated by the lack of inhibition of this process after addition of the PAF-receptor antagonist WEB 2086. We conclude that the movement of neutrophils across airway epithelial cell monolayers occurs preferentially in the physiologic basolateral-to-apical direction, indicating that the polarity of epithelial cells is important for neutrophil transmigration.

CD18 Antigens↗
PubMed1996

Identification of trinucleotide repeat-containing genes in human pancreatic islets.

In the search for diabetes genes, the combined approaches of positional cloning with random markers and subsequent evaluation of candidate genes mapping to areas of interest will be increasingly used. For islet candidate genes of unknown function, expressed trinucleotide (triplet) repeats represent a unique subset. It is unlikely that abnormal expansion of expressed islet triplet repeats would be a major cause of diabetes, yet the triplet repeats are frequently polymorphic and can thus be used to map the genes in the human genome. In this study, a human islet cDNA library was screened with (CGG)7 and (CAG)7, and 23 triplet repeats were isolated. Sequencing revealed four known and six novel islet genes containing 4-15 triplet repeats. The four known cDNAs included ferritin, the major iron-binding protein in cells; HSGSA2R, a full-length clone of the alpha-subunit of the G-regulatory protein; HUMSATB1A, a DNA-binding protein expressed predominantly in thymus; and HUMPPA-PRO, a ribosomal protein. The triplet repeats in ferritin and HUMPPAPRO were found to be monomorphic. Characterization of the six unique novel expressed islet triplet cDNAs revealed that they were 0.6-1.5 kb in size, contained 4-15 triplet repeats, and were expressed in islets and all other tissues examined. Four of the novel clones, CGG-isl 10, CGG-isl 11, CAG-isl 6, and CAG-isl 7, were mapped to human chromosomes 19, 16, 12, and 3, respectively, via somatic cell hybrids. One islet cDNA, CAG-isl 7, contained a repeat that was highly polymorphic, with 14 alleles (4-18 triplets) in African-Americans (heterozygosity = 0.86) and 6 alleles (heterozygosity = 0.77) in whites. Northern analysis indicated that the mRNA was abundant in pancreatic islets. A putative full-length clone contained an open reading frame encoding 213 amino acids with a variable number of alanines (4-18) within the COOH-terminal. The gene was uniquely mapped with odds > 1,000:1 on chromosome 3p in Centre d'Etude du Polymorphisme Humain pedigrees. There were no differences in CAG-isl 7 allele frequencies between African-American patients with NIDDM (n = 108) and control subjects (n = 116), nor was expansion above 18 repeats noted. Linkage analysis in 14 nonglucokinase maturity-onset diabetes of the young pedigrees showed a cumulative logarithm of odds score of -33.19 at theta = 0.00. Abnormal expansion was not observed in 20 IDDM patients with one NIDDM parent. While these data suggest no major role for CAG-isl 7 in diabetes, at least four of the six novel islet triplet genes are coexpressed in pancreatic islets and neural tissue, and these genes can now be considered as candidates for diabetes and/or neuropsychiatric diseases.

Amino Acid Sequence↗
PubMed1996

Isolation, characterization, and chromosomal mapping of the human insulin promoter factor 1 (IPF-1) gene.

Insulin promoter factor 1 (IPF-1) is a homeodomain-containing protein that is thought to be a key regulator of pancreatic islet development and insulin gene transcription in beta-cells. This report describes the isolation and characterization of the human IPF-1 gene. The coding region, which showed 83% nucleotide identity with the mouse IPF-1 gene, was encoded by two exons that extended over a 5-kb region of human genome. The deduced human IPF-1 protein contained 283 amino acids, 1 amino acid less than the mouse IPF-1 protein. The homeodomain region of IPF-1 was encoded by the second exon, and it was highly conserved among species. The human IPF-1 gene was mapped to chromosome 13q12(12.1) by fluorescent in situ hybridization (FISH) analysis. A simple sequence repeat polymorphism (ipf1CA2) was identified in the genomic clone. Polymerase chain reaction (PCR) amplification of this repeat region revealed two alleles (heterozygosity = 0.32). This simple sequence repeat polymorphism, and thus the IPF-1 gene, was incorporated into the human linkage map by genotyping reference Human Polymorphism Study Center (CEPH) pedigrees. Multipoint analysis with the CEPH genotype database placed the gene with equal likelihood between two marker intervals: D13S292-cdx3GA1 and cdx3GA1-D13S289 on chromosome 13, consistent with the results of FISH analysis. Two-point linkage analysis inferred that the most likely location for ipf1CA2 was at theta = 0 from cdx3GA1 locus. The exon-intron boundaries of the IPF-1 gene were sequenced, and primers were synthesized to search the homeodomain region for potential variants in patients with NIDDM. By single-strand conformational polymorphism analysis, no variants were found within this region in 61 Japanese patients, which could contribute to the pathogenesis of NIDDM. The isolation of the human IPF-1 gene, along with characterization of its genomic structure and chromosomal mapping, will now permit the assessment of the role of this gene in the pathogenesis of NIDDM in various populations.

Amino Acid Sequence↗
PubMed1996

Sociodemographic variation in the prevalence of cardiovascular disease.

OBJECTIVE: To estimate the prevalence and social correlates of cardiovascular disease. DESIGN: Population-based cross-sectional survey. Survey data were obtained through a standardized home interview and a clinic visit by trained nurses. The question sequence of the London School of Hygiene (the Rose Questionnaire) was used to identify the presence of definite angina, possible infarction, definite infarction, intermittent claudication and stroke. SETTING: Eight urban communities and rural areas in Saskatchewan in 1990. PARTICIPANTS: A probability sample of 2167 noninstitutionalized men and women aged 18 to 74 years who participated in the Saskatchewan Heart Health Survey. MAIN OUTCOME MEASURES: Prevalence of cardiovascular diseases. RESULTS: Among men, the prevalence of definite angina increased gradually with age from 1.7% (95% CI 0.6% to 2.7%) in the 18 to 34 year group, 3.8% (1.3% to 6.0%) in the 35 to 54 year group to 4.8% (2.8% to 8.3%) in the 55 to 74 year group, while the prevalence among women ranged from 2.5% (1.2 to 3.7%), 4.0% (1.6% to 6.5%) to 7.1% (5.1% to 11.6%) in these same age groups. The prevalence of possible angina, definite infarction, possible infarction and intermittent claudication increased with age as well, being higher in men than in women. Generally, the conditions were more prevalent among those with less education, lower income and those who were unemployed. CONCLUSIONS: These findings indicate that there is sociodemographic inequality in the prevalence of these manifestations of cardiovascular disease, and there is a need for in-depth qualitative research into causal factors in this relationship and for targeted programs of health promotion.

Adult↗
PubMed1996

[Projections from pontine pneumotaxic center to medullary Bötzinger complex in cats].

Experiments were done on 33 adults cats. After injection of WGA-HRP (5%, 30-60 nl) into the Bötzinger complex, labelled cells were observed in the lateral parabrachial nucleus and the Kölliker-Fuse nucleus. Injection into control sites failed to label the cells in the above two nuclei. Ninety-one respiratory related neurons recorded from the pneumotaxic center were tested by electrical stimulation of the Bötzinger complex. Thirteen neurons (14.3%, inspiratory 11, phase-spanning 2) could be antidromically activated. Results of the present study showed that neurons in the pneumotaxic center sent axons to the Bötzinger complex concerning respiratory control.

Animals↗
PubMed1996

Effect of herba artemisiae scopariae on cytogenetic damage induced by aflatoxin B1.

It was found that the per mill rate of micronucleus of marrow cells in mice induced by AFB1 decreased with the increasing dosage of Herba Artemisiae Scopariae, and that there were dosage-effect relations in the lowering of percentage of chromosomal aberration induced by AFB1 and in the inhibition effect on some sister chromatid exchanges per cell.

Aflatoxin B1↗
PubMed1996

Ontogeny and hormonal basis of male-dominant rat hepatic sulfotransferases.

The developmental and hormonal regulation of three male-dominant rat hepatic sulfotransferases (STs) was studied in male and female rats. ST1A1 (phenol ST) mRNA levels increased gradually in both male and female rats after birth until puberty and then declined to a greater extent in female than in male rats. In adult rats, hepatic ST1A1 mRNA levels were approximately 2-3-fold higher in males than in females. However, ST1C1 and ST1E2 mRNAs (corresponding to N-hydroxy-2-acetylaminofluorene ST and estrogen ST, respectively) increased dramatically at puberty in male rats but remained low in female rats. ST1C1 and ST1E2 expression is > 10-fold higher in adult male than in adult female rats. Estradiol, progesterone, and testosterone administration to hypophysectomized rats did not have marked effects on hepatic ST expression. Hypophysectomy decreased ST1A1 gene expression in rat liver, but neither intermittent growth hormone (GH) injection (male pattern) nor continuous GH infusion (female pattern) restored ST1A1 mRNA levels. ST1C1 gene expression was abolished by hypophysectomy and reversed by GH injection. Hypophysectomy did not dramatically decrease hepatic ST1E2 mRNA in male rats but markedly increased ST1E2 expression in female rats. GH infusion (female pattern) in hypophysectomized male and female rats decreased ST1E2 mRNA levels. Prolactin increased hepatic ST1C1 mRNA levels, which is similar to the effect of GH. It is concluded that the three male-dominant rat hepatic STs are regulated differently because the developmental pattern of ST1A1 is markedly different from that for ST1C1 and ST1E2. The high expression of ST1C1 in adult males is determined by male GH secretory pattern, whereas male dominance of ST1E2 is due to the suppressive effect of female GH secretory pattern in adult female rats.

Aging↗
PubMed1996

Identification of human liver cytochrome P450 isoforms involved in the in vitro metabolism of cyclobenzaprine.

Cyclobenzaprine (Flexeril) is a muscle relaxant, possessing a tricyclic structure. Numerous therapeutic agents containing this structure are known to be metabolized by polymorphic cytochrome P4502D6. The aim of this study was to determine if cytochrome P4502D6 and other isoforms are involved in the metabolism of cyclobenzaprine in human liver microsomes. Selective cytochrome P450 inhibitors for CYP1A1/2 (furafylline and 7,8-benzoflavone) and CYP3A4 (troleandomycin, gestodene, and ketoconazole) inhibited the formation of desmethylcyclobenzaprine, a major metabolite of cyclobenzaprine, in human liver microsomes. Antibodies directed against CYP1A1/2 and CYP3A4 inhibited the demethylation reaction whereas anti-human CYP2C9/10, CYP2C19, and CYP2E1 antibodies did not show any inhibitory effects. When a panel of microsomes prepared from human B-lymphoblastoid cells that expressed specific human cytochrome P450 isoforms were used, only microsomes containing cytochromes P4501A2, 2D6, and 3A4 catalyzed N-demethylation. In addition, demethylation catalyzed by these recombinant cytochromes P450 can be completely inhibited with selective inhibitors at concentrations as low as 1 to 20 microM. Interestingly, cyclobenzaprine N-demethylation was significantly correlated with caffeine 3-demethylation (1A2) and testosterone 6 beta-hydroxylation (3A4) but not with dextromethorphan O-demethylation (2D6) in human liver microsomes. To further determine the involvement of cytochrome P4502D6 in cyclobenzaprine metabolism, liver microsomes from a human that lacked CYP2D6 enzyme activities was included in this study. The data showed that cyclobenzaprine N-demethylation still occurred in the incubation with this microsome. These results suggested that cytochrome P4502D6 plays only a minor role in cyclobenzaprine N-demethylation whereas 3A4 and 1A2 are primarily responsible for cyclobenzaprine metabolism in human liver microsomes. Due to the minimum involvement of CYP2D6 in the vitro metabolism of cyclobenzaprine, the polymorphism of cytochrome P4502D6 in man should not be of muci concern in the clinical use of cyclobenzaprine.

Adult↗