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Biomedical subjects

P Li

Publications and source records attributed to P Li.

At least 91 records · Page 5Linked to original sources
PubMed2001

Sialomucin complex (rat Muc4) transmembrane subunit binds the differentiation marker peanut lectin in the normal rat mammary gland.

Sialomucin complex (SMC, rat Muc4) is a heterodimeric glycoprotein composed of two subunits, the mucin component ASGP-1 and the transmembrane subunit ASGP-2. SMC/Muc4 is highly expressed on the surface of 13762 rat mammary adenocarcinoma cells at approximately 100 times the level found in the lactating mammary gland. Immunocytochemical staining of SMC/Muc4 in the developing rat mammary gland is localized to the apical membrane of the ductal epithelium. This staining pattern is similar to that for peanut lectin, a differentiation marker, which binds to cells expressing the disaccharide Thomsen-Friedenreich or TF antigen. Blotting of glycoproteins expressing the TF antigen from mammary tissues with peanut lectin detects a protein matching the migration of ASGP-2. Analysis of immunoprecipitated SMC/Muc4 by peanut lectin blotting shows that the TF antigen is abundantly present on the ASGP-2 subunit, hence the similarity of staining pattern with SMC/Muc4 antisera and peroxidase-conjugated lectin in mammary tissues. The TF antigen is also present on ASGP-2 of SMC/Muc4 produced by confluent cultures of Rama 37 rat mammary epithelial stem cells after their induction to an alveolar-like phenotype with prolactin. These results indicate that the TF antigen is present on the ASGP-2 transmembrane subunit of SMC/Muc4 from phenotypically normal tissues and cells, in contrast to malignant cells whose peanut lectin-binding disaccharide is located on ASGP-1.

Animals↗
PubMed2001

Determination of nucleosides in natural Cordyceps sinensis and cultured Cordyceps mycelia by capillary electrophoresis.

Cordyceps sinensis is a well-known traditional Chinese medicine, and some of the active components are nucleosides. The analysis of nucleosides in Cordyceps material has been performed by reversed-phase high-performance liquid chromatography (HPLC) with gradient elution or by spectrometry. Here, we have explored the possibility of using capillary electrophoresis to determine the content of three major nucleosides (adenosine, guanosine and uridine) in Cordyceps. Capillary electrophoresis needs no gradients, and it provides a better separation due to its higher efficiency. In order to optimize the resolution, the separation of adenosine, guanosine and uridine was determined in Cordyceps with respect to the variation of buffer concentration, pH, temperature, and voltage. By using the calibrated electrophoresis system, the separation was achieved for the three nucleosides in less than 10 min with a background electrolyte consisting of 0.2 M boric acid-sodium hydroxide buffer, pH 8.5. The nucleoside contents of various types of natural Cordyceps and cultured Cordyceps mycelia were determined and compared. There was a great variation of nucleoside content in different sources of Cordyceps; the cultured Cordyceps mycelia, however, contains a much higher concentration than the natural Cordyceps.

Adenosine↗
PubMed2001

Balloon atrial septostomy in end-stage pulmonary hypertension guided by a novel intracardiac echocardiographic transducer.

Blade and balloon atrial septostomy has been used to reduce cardiopulmonary symptoms and as a bridge to lung or heart lung transplant in primary pulmonary hypertension. Due to severe right atrial dilatation and resultant loss of anatomical landmarks, the procedure is technically difficult, and the reported postprocedure mortality rate varies between 5% and 50%. Among others, marked systemic desaturation and systemic hypotension presumably secondary to an excessively large atrial septal defect have been reported as causes of postprocedure death. We report a case where a novel intracardiac catheter-based phased-array 5.5--10 MHz transducer with spectral and color-flow Doppler capabilities was used to assist a balloon atrial septostomy and to obtain hemodynamic data in a patient with end-stage pulmonary hypertension.

Catheterization↗
PubMed2001

Glycosylated and phosphorylated proteins--expression in yeast and oocytes of Xenopus: prospects and challenges--relevance to expression of thermostable proteins.

Phosphorylation and glycosylation are important posttranslational events in the biosynthesis of proteins. The different degrees of phosphorylation and glycosylation of proteins have been an intriguing phenomenon. Advances in genetic engineering have made it possible to control the degree of glycosylation and phosphorylation of proteins. Structural biology of phosphorylated and glycosylated proteins has been advancing at a much slower pace due to difficulties in using high-resolution NMR studies in solution phase. Major difficulties have arisen from the inherent mobilities of phosphorylated and glycosylated side chains. This paper reviews molecular and structural biology of phosphorylated and glycosylated proteins expressed in eukaryotic expression systems which are especially suited for large-scale production of these proteins. In our laboratory, we have observed that eukaryotic expression systems are particularly suited for the expression of thermostable light-activated proteins, e.g., bacteriorhodopsins and plastocyanins.

Animals↗
PubMed2001

Forskolin modulation of desensitization at GABA(A) and glycine receptors is not mediated by cAMP-dependent protein kinase in isolated carp amacrine-like cells.

The effects of forskolin on gamma-aminobutyric acid type-A (GABA(A)) and glycine receptors in amacrine-like cells of carp (Carassius auratus) retina were studied using patch-clamp techniques. Application of 50 microM forskolin markedly accelerated the desensitization of whole-cell responses induced by 100 microM GABA or glycine without changing the peak amplitude of the response. Both 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) and 3-isobutyl-1 -methylxanthine (IBMX) (500 microM) failed to accelerate the desensitization of these two receptors. Protein kinase A (PKA) inhibitors, N- [2-[(p-bromocinnamyl)amino]ethyl)-5-isoquinolinesulfonamide dihydrochloride (H-89) and N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H-8), could not block these effects of forskolin. An inactive analogue of forskolin, 1,9-dideoxyforskolin (DFSK), accelerated the desensitization effectively. These results suggest that forskolin's effects are not mediated by activation of the PKA pathway. Moreover, similar results were obtained using excised outside-out patches of these cells, suggesting that forskolin may act on an extracellular site(s). The neurosteroids 5alpha-pregnane-3alpha,21 -diol-20-one (THDOC) and 5-pregnen-31 -ol-20-one sulfate sodium (PS), structural analogues of forskolin, accelerated the desensitization of these receptors without changing the peak amplitudes, thus mimicking forskolin's effects. Furthermore, PS interacted with forskolin on these receptors so as to slow down the responses. These results raise the possibility that forskolin acts directly on an extracellular site(s) of the GABA(A) and glycine receptors, shared with neurosteroids, in carp amacrine-like cells.

Animals↗
PubMed2001

Effect of deletion and the site of insertion in double copy anti-tat retroviral vectors: viral titres and production of anti-tat mRNA.

In attempts to further develop murine leukemia virus (MLV) based retroviral vectors for gene therapy, we investigated vector production and antisense expression from retroviral constructs with U3 deletions or insertions. Promoter elements in the U3 region of the 3' LTR of the vector pLXSN were deleted and replaced with DNA encoding the HIV anti-tat gene under control of the tRNAmet promoter to produce a double copy self inactivating vector (DC-SIN). DC-SIN constructs were compared to vectors containing the anti-tat cassette inserted at 5 different sites of the U3 region (DC-insertions). Titres of DC-SIN and DC-insertion vectors were similar but approximately 10 fold lower than parental pLXSN. Cells transduced with DC-SIN and DC-insertion vectors all expressed anti-tat mRNA. Transcripts from the MLV-LTR were detected in cells transduced with DC-insertion but not DC-SIN vectors or a vector with the anti-tat cassette between CAAT and TATA boxes of the promoter, indicating inactivation of the viral promoter in the latter vectors. Cells transduced with constructs of either design showed comparable efficacy of protection against HIV challenge. Thus, no U3 insertion site was preferred for virus production. Insertion of a tRNA promoter between CAAT and TATA boxes and the DC-SIN design which would not introduce an active RNA pol II promoter into the genome are attractive for further development of safe gene therapy agents.

Genes, tat↗
PubMed2001

HIV DNA integration during cell-to-cell transmission of infection: evidence for partially integrated DNA structures in acutely infected cells.

A one-step cell-to-cell transmission model of human immunodeficiency virus (HIV) infection was used to study viral DNA integration in the early phase of viral replication. Co-culturing H3B cells as virus donors with CD4+ Hut78 recipient cells in a ratio of 1:4 produced a synchronous, one-step viral infection with de novo synthesis of unintegrated HIV DNA within 4 h p.i., which subsequently integrates in the host genomic DNA to form provirus. To study the kinetics of viral DNA integration, cellular chromosomal DNA was isolated at different times after co-culturing and extensive electrophoresis was used to remove residual unintegrated viral DNA. Removal of contaminating, unintegrated viral DNA in the purified chromosomal DNA fraction was confirmed by various experiments. When purified chromosomal DNA (free of contaminating unintegrated viral DNA)--from the mix of acutely infected cells--was digested with restriction enzymes KpnI, BamHI or PstI and analysed by Southern blot hybridization, integration of viral DNA into chromosomal DNA was first observed at 8 h p.i. and was essentially complete by 72 h p.i. In addition, evidence was found for a relatively stable, partially integrated HIV DNA structure within the chromosomal DNA, that was first detectable at 8 h p.i. and did not become fully integrated until 72 hours post infection.

Blotting, Southern↗
PubMed2001

Cholinergic, noradrenergic, and serotonergic inhibition of fast synaptic transmission in spinal lumbar dorsal horn of rat.

It is known that spinal nociceptive sensory transmission receives descending inhibitory and facilitatory modulation from supraspinal structures. Glutamate is the major fast excitatory transmitter between primary afferent fibers and spinal dorsal horn neurons. In whole-cell patch clamp recordings from dorsal horn neurons in spinal slices, we investigated synaptic mechanisms for inhibitory modulation at the lumbar level of the spinal cord. Application of the cholinergic receptor agonist carbachol produced a dose-dependent inhibition of glutamate-mediated excitatory postsynaptic currents (EPSCs) (IC(50) 13 microM). Postsynaptic injection of two different types of G-protein inhibitors, guanosine 5'-O-2-thiophosphate or guanosine 5'-O-3-thiotriphosphate, blocked the inhibition produced by carbachol. Clonidine, a selective alpha-adrenergic receptor agonist, also produced a dose-dependent inhibition of EPSCs (IC(50) 7 microM) that was reduced by postsynaptic inhibition of G-proteins. The inhibitory effect of serotonin was likewise mediated by postsynaptic G-proteins. Our results suggest that activation of postsynaptic neurotransmitter receptors plays a critical role in inhibition of glutamate mediated sensory responses by acetylcholine, norepinephrine, and serotonin. Our results support the hypothesis that descending sensory modulation may be mediated by multiple neurotransmitter receptors in the spinal cord.

Acetylcholine↗
PubMed2001

The 5-HT(6) receptor antagonist SB-271046 selectively enhances excitatory neurotransmission in the rat frontal cortex and hippocampus.

Preclinical evidence has suggested a possible role for the 5-HT(6) receptor in the treatment of cognitive dysfunction. However, currently there is little neurochemical evidence suggesting the mechanism(s) which may be involved. Using the selective 5-HT(6) antagonist SB-271046 and in vivo microdialysis, we have evaluated the effects of this compound on the modulation of basal neurotransmitter release within multiple brain regions of the freely moving rat. SB-271046 produced no change in basal levels of dopamine (DA), norepinephrine (NE) or 5-HT in the striatum, frontal cortex, dorsal hippocampus or nucleus accumbens. Similarly, this compound had no effect on excitatory neurotransmission in the striatum or nucleus accumbens. Conversely, SB-271046 produced 3- and 2-fold increases in extracellular glutamate levels in both frontal cortex and dorsal hippocampus, respectively. These effects were completely attenuated by infusion of tetrodotoxin but unaffected by the muscarinic antagonist, atropine. Here we demonstrate for the first time the selective enhancement of excitatory neurotransmission by SB-271046 in those brain regions implicated in cognitive and memory function, and provide mechanistic evidence in support of a possible therapeutic role for 5-HT(6) receptor antagonists in the treatment of cognitive and memory dysfunction.

Animals↗
PubMed2001

The transcription factors L-Sox5 and Sox6 are essential for cartilage formation.

L-Sox5 and Sox6 are highly identical Sry-related transcription factors coexpressed in cartilage. Whereas Sox5 and Sox6 single null mice are born with mild skeletal abnormalities, Sox5; Sox6 double null fetuses die with a severe, generalized chondrodysplasia. In these double mutants, chondroblasts poorly differentiate. They express the genes for all essential cartilage extracellular matrix components at low or undetectable levels and initiate proliferation after a long delay. All cartilages are thus extracellular matrix deficient and remain rudimentary. While chondroblasts in the center of cartilages ultimately activate prehypertrophic chondrocyte markers, epiphyseal chondroblasts ectopically activate hypertrophic chondrocyte markers. Thick intramembranous bone collars develop, but the formation of cartilage growth plates and endochondral bones is disrupted. L-Sox5 and Sox6 are thus redundant, potent enhancers of chondroblast functions, thereby essential for endochondral skeleton formation.

Animals↗
PubMed2001

The development of highly efficient onium-type peptide coupling reagents based upon rational molecular design.

Novel and highly efficient immonium-, pyridinium- and thiazolium-type peptide coupling reagents, such as BOMI, BDMP, BPMP, BEP, FEP, BEPH, FEPH and BEMT, were developed by rational modifying of the molecular structures of commonly used uronium-type reagents. The high efficiency of these onium salts has been evaluated and proven by model reaction tests and the successful synthesis of various oligopeptides and biologically active peptides, both in solution and in the solid-phase, for example Leu-enkephalin, the pentapeptide moiety of Dolastatin 15 and the immunosuppressive undecapeptide cyclosporin O. Based upon these results, the relationship between the molecular structure and the capability of onium-type peptide coupling reagents was studied. A preliminary guideline for the molecular design of onium-type coupling reagents was developed.

Chromatography, High Pressure Liquid↗
PubMed2001

Complex structure of the activating immunoreceptor NKG2D and its MHC class I-like ligand MICA.

The major histocompatibility complex (MHC) class I homolog, MICA, is a stress-inducible ligand for NKG2D, a C-type lectin-like activating immunoreceptor. The crystal structure of this ligand-receptor complex that we report here reveals an NKG2D homodimer bound to a MICA monomer in an interaction that is analogous to that seen in T cell receptor-MHC class I protein complexes. Similar surfaces on each NKG2D monomer interact with different surfaces on either the alpha1 or alpha2 domains of MICA. The binding interactions are large in area and highly complementary. The central section of the alpha2-domain helix, disordered in the structure of MICA alone, is ordered in the complex and forms part of the NKG2D interface. The extensive flexibility of the interdomain linker of MICA is shown by its altered conformation when crystallized alone or in complex with NKG2D.

Amino Acid Sequence↗
PubMed2001

Transcriptome of channel catfish (Ictalurus punctatus): initial analysis of genes and expression profiles of the head kidney.

Analysis of expressed sequence tags (ESTs) is an efficient approach for gene discovery, expression profiling, and development of resources useful for functional genomics studies. As part of the transcriptome analysis in channel catfish (Ictalurus punctatus), we have conducted EST analysis using a cDNA library made from the head kidney. We analysed 2228 EST clones. Orthologues were established for 1495 (67.1%) clones representing 748 genes, of which 545 (36.5%) clones were singletons. The remaining 733 (32.9%) clones represent unknown gene clones, for which the number of genes has not yet been determined.

Animals↗
PubMed2001

Three-dimensional echocardiography of left atrial appendage thrombus.

Transesophageal echocardiography (TEE) is superior to transthoracic echocardiography (TTE) in evaluating the left atrial appendage (LAA) as a potential cardiac source of embolus in patients with stroke. We describe two such patients in whom a TEE and subsequently a three-dimensional (3-D) reconstruction of the LAA were performed. These case reports show that 3-D echocardiography provides better visualization of LAA anatomy, and that a 3-D description of LAA morphology may be the basis of describing normal and abnormal LAA.

Aged↗
PubMed2001

Power Doppler myocardial contrast echocardiography using an improved multiple frame triggered Harmonic Angio technique.

Although B-mode harmonic, intermittent-triggered myocardial contrast echocardiography (MCE) is a well-established technique, a variety of MCE techniques have been introduced recently to improve myocardial opacification. One such technique uses a power Doppler method in conjunction with multiple frame triggering (MFT), but has been limited by nonuniform microbubble destruction and blooming as well as motion artifacts. Utilizing two different contrast agents, Definity and Optison, we tested the feasibility of an improved version of Harmonic Angio MFT that utilizes a lower transmit frequency, reduced packet size, and more stringent wall filter in normal volunteers and in patients with known perfusion defects. The results showed that Harmonic Angio MFT produced fill frames with readily visible opacification and destruction frames with little visible opacification. The patterns of opacification also correlated with the expected perfusion patterns in both groups of subjects. Thus, Harmonic Angio MFT appears to be a promising new MCE technique.

Adult↗
PubMed2001

Primary transanal rectosigmoidectomy for Hirschsprung's disease: Preliminary results in the initial 33 cases.

PURPOSE: The authors describe their newly developed technique-primary transanal rectosigmoidectomy for Hirschsprung's disease (HD) and its preliminary results in neonates and infants. METHODS: Thirty-four consecutive patients (26 boys) with biopsy-proven rectosigmoid HD, aged 18 days to 4 years, underwent this new procedure. Rectal mucosectomy started 1 to 1.5 cm posteriorly and 2 to 3 cm anteriorly proximal to the dentate line. The rectal muscular sleeve below the peritoneal reflection was resected to the level of the striated muscle complex, leaving a shorter muscular cuff, into which a partial internal sphincterotomy was made posteriorly. An oblique anastomosis was constructed between the pull-through ganglionic colon and the anus canal. RESULTS: The mean time for the operation was 160 minutes, and the average length of bowel resected was 29.5 cm (range, 12.5 to 41 cm). Two children (6.06%, 2 of 33) had 2 to 5 episodes of postoperative enterocolitis (EC). One was cured by rectal irrigation and dilation, and the another by Lynn's myectomy. Eighty-four percent of patients had 1 to 6 bowel movements per day during a 6- to 18-month follow-up period. CONCLUSIONS: Primary transanal rectosigmoidectomy for HD is logical and associated with excellent early results. A long-term follow-up is required to determine bowel functions. J Pediatr Surg 36:1816-1819.

Anal Canal↗