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Biomedical subjects

L Xu

Publications and source records attributed to L Xu.

At least 451 records · Page 25Linked to original sources
PubMed1998

Infection of human primary renal epithelial cells with HIV-1 from children with HIV-associated nephropathy.

Children affected with human immunodefficiency virus (HIV)-associated nephropathy (HIVAN) usually develop significant renal glomerular and tubular epithelial cell injury. The pathogenesis of these changes is not clearly understood. Human renal tubular epithelial cells (RTEc) do not express CD4 surface receptors, and it is not clear whether these cells can be infected by HIV-1. Certain strains of HIV-1, however, have been shown capable of infecting CD4-negative epithelial cell lines. We hypothesized that the inability of laboratory strains of HIV-1 to infect renal epithelial cells may be due to a limited tropism, as opposed to wild-type viruses derived from children with HIVAN, and that viruses derived from these children are capable of infecting RTEc from the same patient. Here, we have demonstrated that HIV-1 isolates from children with HIVAN can productively infect RTEc through a CD4 independent pathway, and that infected mononuclear cells can transfer the virus to human RTEc. Human RTEc sustained low levels of viral replication and HIV-1 inhibited the growth and survival of cultured human RTEc. Thus, HIV-1 may directly induce degenerative changes in RTEc of children with HIVAN. Infected macrophages may play a relevant role in this process by transferring viruses to RTEc.

AIDS-Associated Nephropathy↗
PubMed1998

Imperatoxin A induces subconductance states in Ca2+ release channels (ryanodine receptors) of cardiac and skeletal muscle.

Single-channel and [3H]ryanodine binding experiments were carried out to examine the effects of imperatoxin activator (IpTxa), a 33 amino acid peptide isolated from the venom of the African scorpion Pandinus imperator, on rabbit skeletal and canine cardiac muscle Ca2+ release channels (CRCs). Single channel currents from purified CRCs incorporated into planar lipid bilayers were recorded in 250 mM KCl media. Addition of IpTxa in nanomolar concentration to the cytosolic (cis) side, but not to the lumenal (trans) side, induced substates in both ryanodine receptor isoforms. The substates displayed a slightly rectifying current-voltage relationship. The chord conductance at -40 mV was approximately 43% of the full conductance, whereas it was approximately 28% at a holding potential of +40 mV. The substate formation by IpTxa was voltage and concentration dependent. Analysis of voltage and concentration dependence and kinetics of substate formation suggested that IpTxa reversibly binds to the CRC at a single site in the voltage drop across the channel. The rate constant for IpTxa binding to the skeletal muscle CRC increased e-fold per +53 mV and the rate constant of dissociation decreased e-fold per +25 mV applied holding potential. The effective valence of the reaction leading to the substate was approximately 1.5. The IpTxa binding site was calculated to be located at approximately 23% of the voltage drop from the cytosolic side. IpTxa induced substates in the ryanodine-modified skeletal CRC and increased or reduced [3H]ryanodine binding to sarcoplasmic reticulum vesicles depending on the level of channel activation. These results suggest that IpTxa induces subconductance states in skeletal and cardiac muscle Ca2+ release channels by binding to a single, cytosolically accessible site different from the ryanodine binding site.

Animals↗
PubMed1998

Effect of heart failure on muscle capillary geometry: implications for 02 exchange.

UNLABELLED: There is strong evidence that chronic heart chronic heart failure (CHF) impairs skeletal muscle function independent of blood flow and bulk O2 delivery. PURPOSE: This investigation sought to determine whether alterations in muscle capillary geometry and surface area that are thought to be primary determinants of the efficacy for blood-tissue 02 exchange might be altered in CHF and contribute to these changes. METHODS: Plantaris (fast twitch) and soleus (slow twitch) muscles from control (C) and 6- to 7-wk post myocardial infarcted (CHF) rates were perfusion-fixed in situ. These muscles were analyzed using morphometric techniques that facilitated determination of muscle sarcomere length fiber cross-sectional area, capillary tortuosity and branching coefficient (c(K,0)), capillary length, volume, and surface area. RESULTS: Normalized to a sarcomere length of 2.1 microns, plantaris fiber cross-sectional area decreased by 21% (P < 0.05), and capillary-to-fiber ratio decreased from 2.05 +2- 0.07 in C to 1.79 +2- 0.04 (P < 0.05) in CHF, but these variables were unchanged in soleus. These was no change in c(K,0) or capillary diameter in either muscle, and thus capillary length and surface area per fiber volume remained unchanged. From the measured fiber atrophy and capillary involution in plantaris reductions of total muscle capillary length, volume, and surface area of 11%, 9% and 17%, respectively, are estimated. CONCLUSION: These changes, coupled with reduced blood flow may impair the effective matching of muscle fiber 02 delivery to 02 requirement during repeated muscle contractions (i.e. exercise). The scenario is expected to reduce intramyocyte 02 partial pressure and thereby contribute to the greater fatigability characteristic of the CHF condition.

Animals↗
PubMed1998

Biochemical analysis of the secreted and virion glycoproteins of Ebola virus.

The glycoproteins expressed by a Zaire species of Ebola virus were analyzed for cleavage, oligomerization, and other structural properties to better define their functions. The 50- to 70-kDa secreted and 150-kDa virion/structural glycoproteins (SGP and GP, respectively), which share the 295 N-terminal residues, are cleaved near the N terminus by signalase. A second cleavage event, occurring in GP at a multibasic site (RRTRR downward arrow) that is likely mediated by furin, results in two glycoproteins (GP1 and GP2) linked by disulfide bonding. This furin cleavage site is present in the same position in the GPs of all Ebola viruses (R[R/K]X[R/K]R downward arrow), and one is predicted for Marburg viruses (R[R/K]KR downward arrow), although in a different location. Based on the results of cross-linking studies, we were able to determine that Ebola virion peplomers are composed of trimers of GP1-GP2 heterodimers and that aspects of their structure are similar to those of retroviruses, paramyxoviruses, and influenza viruses. We also determined that SGP is secreted from infected cells almost exclusively in the form of a homodimer that is joined by disulfide bonding.

Animals↗
PubMed1998

Endogenous ANG II supports lumbar sympathetic activity in conscious sodium-deprived rats: role of area postrema.

This study tests the hypothesis that the area postrema (AP) is necessary for endogenous ANG II to chronically maintain lumbar sympathetic nerve activity (LSNA) and heart rate (HR) in conscious sodium-deprived rats. The effect of the ANG II type 1-receptor antagonist, losartan, on LSNA and HR was determined in rats that were either AP lesioned (APX) or sham lesioned. The sham rats were divided into groups, with (SFR) or without (SAL) food restriction, to control for the decreased food intake of APX rats. Before losartan, basal mean arterial pressure (MAP), HR, and baroreflex control of LSNA and HR were similar between groups, with the exception of lower maximal reflex LSNA and higher maximal gain of the HR-MAP curve in APX rats. In all groups, losartan similarly shifted (P < 0.01) the LSNA-MAP curve to the left without altering maximal gain. Losartan also decreased (P < 0.05) minimal LSNA in all groups, and suppressed (P < 0.01) maximal LSNA (% of control) in SFR (240 +/- 13 to 205 +/- 15) and SAL (231 +/- 21 to 197 +/- 26) but not APX (193 +/- 10 to 185 +/- 8) rats. In general, losartan similarly shifted the HR-MAP curve to a lower MAP in all groups. The results suggest that the AP is not necessary for endogenous ANG II to chronically support LSNA and HR at basal and elevated MAP levels in sodium-deprived rats. However, the AP is required for endogenous ANG II to increase maximal reflex LSNA at low MAP levels.

Angiotensin II↗
PubMed1998

Codes for sound-source location in nontonotopic auditory cortex.

We evaluated two hypothetical codes for sound-source location in the auditory cortex. The topographical code assumed that single neurons are selective for particular locations and that sound-source locations are coded by the cortical location of small populations of maximally activated neurons. The distributed code assumed that the responses of individual neurons can carry information about locations throughout 360 degrees of azimuth and that accurate sound localization derives from information that is distributed across large populations of such panoramic neurons. We recorded from single units in the anterior ectosylvian sulcus area (area AES) and in area A2 of alpha-chloralose-anesthetized cats. Results obtained in the two areas were essentially equivalent. Noise bursts were presented from loudspeakers spaced in 20 degrees intervals of azimuth throughout 360 degrees of the horizontal plane. Spike counts of the majority of units were modulated >50% by changes in sound-source azimuth. Nevertheless, sound-source locations that produced greater than half-maximal spike counts often spanned >180 degrees of azimuth. The spatial selectivity of units tended to broaden and, often, to shift in azimuth as sound pressure levels (SPLs) were increased to a moderate level. We sometimes saw systematic changes in spatial tuning along segments of electrode tracks as long as 1.5 mm but such progressions were not evident at higher sound levels. Moderate-level sounds presented anywhere in the contralateral hemifield produced greater than half-maximal activation of nearly all units. These results are not consistent with the hypothesis of a topographic code. We used an artificial-neural-network algorithm to recognize spike patterns and, thereby, infer the locations of sound sources. Network input consisted of spike density functions formed by averages of responses to eight stimulus repetitions. Information carried in the responses of single units permitted reasonable estimates of sound-source locations throughout 360 degrees of azimuth. The most accurate units exhibited median errors in localization of <25 degrees, meaning that the network output fell within 25 degrees of the correct location on half of the trials. Spike patterns tended to vary with stimulus SPL, but level-invariant features of patterns permitted estimates of locations of sound sources that varied through 20-dB ranges. Sound localization based on spike patterns that preserved details of spike timing consistently was more accurate than localization based on spike counts alone. These results support the hypothesis that sound-source locations are represented by a distributed code and that individual neurons are, in effect, panoramic localizers.

Action Potentials↗
PubMed1998

Sensitivity to sound-source elevation in nontonotopic auditory cortex.

We have demonstrated that the spike patterns of auditory cortical neurons carry information about sound-source location in azimuth. The question arises as to whether those units integrate the multiple acoustical cues that signal the location of a sound source or whether they merely demonstrate sensitivity to a specific parameter that covaries with sound-source azimuth, such as interaural level difference. We addressed that issue by testing the sensitivity of cortical neurons to sound locations in the median vertical plane, where interaural difference cues are negligible. Auditory unit responses were recorded from 14 alpha-chloralose-anesthetized cats. We studied 113 units in the anterior ectosylvian auditory area and 82 units in auditory area A2. Broadband noise stimuli were presented in an anechoic room from 14 locations in the vertical midline in 20 degrees steps, from 60 degrees below the front horizon, up and over the head, to 20 degrees below the rear horizon, as well as from 18 locations in the horizontal plane. The spike counts of most units showed fairly broad elevation tuning. An artificial neural network was used to recognize spike patterns, which contain both the number and timing of spikes, and thereby estimate the locations of sound sources in elevation. For each unit, the median error of neural-network estimates was used as a measure of the network performance. For all 195 units, the average of the median errors was 46.4 +/- 9.1 degrees (mean +/- SD), compared with the expectation of 65 degrees based on chance performance. To address the question of whether sensitivity to sound pressure level (SPL) alone might account for the modest sensitivity to elevation of neurons, we measured SPLs from the cat's ear canal and compared the neural elevation sensitivity with the acoustical data. In many instances, the artificial neural network discriminated stimulus elevations even when the free-field sound produced identical SPLs in the ear canal. Conversely, two stimuli at the same elevation could produce the same network estimate of elevation, even when we varied sound-source SPL over a 20-dB range. There was a significant correlation between the accuracy of network performance in azimuth and in elevation. Most units that localized well in elevation also localized well in azimuth. Because the principal acoustic cues for localization in elevation differ from those for localization in azimuth, that positive correlation suggests that individual cortical neurons can integrate multiple cues for sound-source location.

Action Potentials↗
PubMed1998

Intermediate myasthenia syndrome following acute organophosphates poisoning--an analysis of 21 cases.

1. Twenty-one cases out of 272 patients of acute organophosphates poisoning were diagnosed as intermediate syndrome (IMS) with a prevalence at 7.7%. The responsible OP insecticides included parathion, omethoate and some OP containing pesticide mixtures. IMS occurred mainly in severe OP poisoning patients who recovered from the acute cholinergic crisis at 7-75 h after the onset of acute poisoning. 2. Muscular weakness appeared in the following three categories of muscles: (1) neck flexors and proximal limb muscles; (2) muscles innervated by motor cranial nerves and/or (3) respiratory muscles. Blood acetylcholinesterase activity was persistently inhibited. Electroneuromyography (ENMG) with repetitive nerve stimulation (RNS) at frequencies of 20 Hz or 30 Hz in seven patients showed decrements of common muscle action potentials during the presence of myasthenia in five patients and became normal when their muscle strength recovered. 3. Mild IMS recovered within 2-7 days and had a favorable prognosis. Severe IMS patients with respiratory paralysis needed immediate endotracheal intubation and mechanical ventilation. Recovery of weakness of the respiratory muscles and proximal limb muscles took longer, the slowest being 30 days. Four of the patients died of respiratory paralysis and the fatality rate was 19%. 4. The mechanism of IMS remains to be further investigated. The RNS/ENMG changes indicate a post-synaptic block at the neuromuscular junctions. 5. In order to promote the recognition of this syndrome, we proposed to name the syndrome as Intermediate Myasthenia Syndrome (IMS).

Adolescent↗
PubMed1998

The epidemiology study of hyperuricemia and gout in a community population of Huangpu District in Shanghai.

OBJECTIVE: To investigate the prevalence of hyperuricemia and gout in a community population of Huangpu District in Shanghai. METHODS: In the target community, 2037 dwellers were interviewed with relevan questionnares from house to house. According to even house number 1017 blood samples were taken for serum uric acid (SUA) levels measured with the uricase-peroxidase enzymatic method. RESULTS: The prevalence of hyperuricemia was 14.2% in men (SUA > 70 mg/L, 62 cases), 7.1% in women (SUA > 60 mg/L, 41 cases), 10.1% in both sexes. Seven gout patients were all men. The prevalence of gout in 2037 dwellers in Huangpu District was 0.77% in men and 0.34% in both sexes. CONCLUSIONS: The mean SUA level in each age group in this survey was much higher than that of a previous study 1 carried out in Shanghai, Beijing and Guangzhou in 1980 (P < 0.05). And the prevalence of hyperuricemia was increased rapidly (in men: from 1.4% in the survey of 1980 to 14.2% in our survey; in women: from 1.3% in the survey of 1980 to 7.1% in our survey). Compared with Idonesia data in 1992, the prevalence of hyperuricemia and gout in our survey was lower than that in Indonesia (P < 0.05), which suggests that racial and genetic predispositions are key causative factors.

Adolescent↗
PubMed1998

[Mifepristone in the treatment of 47 ectopic pregnancy patients].

OBJECTIVE: To investigate the effect and indication of mifepristone in treating ectopic pregnancy, 47 patients were divided into three groups. RESULTS: Twenty-nine cases were effective; 18 cases were ineffective and operated on in which we observed the gestational termination, bleeding capacity, and pathological changes in fallopian tube. We found that the effect was related to the drug dosage, levels of beta-hCG in blood and the operating time. CONCLUSION: High dosage of mifepristone in treating ectopic pregnancy is convenient, safe, and has no side-effects. It is suitable for patients with early ectopic pregnancy who have smooth life-sign, beta-hCG < 10 ng.ml-1, the mass in pelvic cavity < or = 5 cm, without acute belly-ache and pulsation of fetal heart in fallopian tube and who ask for the conservative treatment.

Abortifacient Agents, Steroidal↗
PubMed1998

[Protective effects of shenmai cardioplegia on intracardiac operative patients with cardiopulmonary bypass].

Forty intracardiac-operative patients were divided into two groups randomly. Twenty patients were received by the improved St. Thomas Crystal Blood (1:4) Cardioplegia(Group A); 20 by the Shenmai liquid and improved St. Thomas Crystal Blood(1:4) Cardioplegia(Group B). During perioperation, the blood samples and myocardial tissue were collected, and clinical observations were recorded. The results showed that in Group B, contents of myocardial specific isoenzyme of creatine kinase(CK-MB), lactate dehydrogenase(LDH), malonyldialdehyde(MDA), and myocardial Ca2+ were significantly lower, the contents of superoxide dismutase(SOD) were, significantly better than that in Group A; and the histological findings showed less damage in Group B than in Group A. We conclude that Shenmai Cardioplegia can increase the myocardial protection of the intracardiac-operative patients. The possible mechanisms are that Shenmai liquids inhibit the production of oxygen free radicals and calcium paradox.

Adolescent↗
PubMed1998

[Immobilization of rat liver microsomes with liquid lipid membrane encapsulation].

Rat liver microsomes were immobilized by encapsulating them into liquid lipid membranes (56% paraffin thick, 38% paraffin thin, 5% lecthin and 1% dodecanol). The resistance against heat and pH profile of the immobilized enzyme-NADPH-cytochrome C reductase was weakened. However, the activity and storage stability of the immobilized enzyme were enhanced.

Animals↗
PubMed1998

[Molecular cloning of EXT2 and EXT4 gene].

Hereditary multiple exostose(EXT) is an autosomal dominant disorder of skeletal system. Three genetic loci have been identified at 8q24.1(EXT1), 11p11(EXT2) and 19p(EXT3) respectively. In this paper, EXT2 gene was cloned with positional cloning and homologous screening. SSCP and sequencing analysis have been done in 37 EXT patients who came from 20 EXT families, 2 mutations of insertion were tested in 2 patients. This confirmed that the gene cloned in this paper was EXT2 gene which locus at 11p11. Additionally EXT4 gene was cloned with homologous screening and located at 1p36.1 with FISH in this paper.

Amino Acid Sequence↗
PubMed1998

[Immunohistochemical study of Cath-D and CD44 in laryngeal squamous cell carcinomas].

The expression of Cath-D and CD44 was examined immunohistochemically in 96 laryngeal squamous cell carcinomas and compared with clinic pathological feature. Expression of Cath-D and CD44 was detected in 52.1% and 41.7% respectively. The correlation was observed between Cath-D expression and metastasis (including lymph node metastasis and distant metastasis), but Cath-D expression was not associated with lymph node metastasis. Expression of CD44 was not associated with lymph node metastasis also. In addition, expression of Cath-D and CD44 did not correlated with clinical stage, histologic grade, size of tumor and postoperative 3 years survival rates. Our results indicate that Cath-D may play a role in metastasis.

Adult↗