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Biomedical subjects

C Li

Publications and source records attributed to C Li.

At least 667 records · Page 37Linked to original sources
PubMed1998

Regulation of catch muscle by twitchin phosphorylation: effects on force, ATPase, and shortening.

Recent experiments on permeabilized anterior byssus retractor muscle (ABRM) of Mytilus edulis have shown that phosphorylation of twitchin releases catch force at pCa > 8 and decreases force at suprabasal but submaximum [Ca2+]. Twitchin phosphorylation decreases force with no detectable change in ATPase activity, and thus increases the energy cost of force maintenance at subsaturating [Ca2+]. Similarly, twitchin phosphorylation causes no change in unloaded shortening velocity (Vo) at any [Ca2+], but when compared at equal submaximum forces, there is a higher Vo when twitchin is phosphorylated. During calcium activation, the force-maintaining structure controlled by twitchin phosphorylation adjusts to a 30% Lo release to maintain force at the shorter length. The data suggest that during both catch and calcium-mediated submaximum contractions, twitchin phosphorylation removes a structure that maintains force with a very low ATPase, but which can slowly cycle during submaximum calcium activation. A quantitative cross-bridge model of catch is presented that is based on modifications of the Hai and Murphy (1988. Am. J. Physiol. 254:C99-C106) latch bridge model for regulation of mammalian smooth muscle.

Adenosine Triphosphatases↗
PubMed1998

A physicochemical approach for predicting the effectiveness of peptide-based gene delivery systems for use in plasmid-based gene therapy.

Novel synthetic peptides, based on carrier peptide analogs (YKAKnWK) and an amphipathic peptide (GLFEALLELLESLWELLLEA), have been formulated with DNA plasmids to create peptide-based gene delivery systems. The carrier peptides are used to condense plasmids into nanoparticles with a hydrodynamic diameter (DH) ranging from 40 to 200 nm, which are sterically stable for over 100 h. Size and morphology of the carrier peptide/plasmid complex have been determined by photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM), respectively. The amphipathic peptide is used as a pH-sensitive lytic agent to facilitate release of the plasmid from endosomes after endocytosis of the peptide/plasmid complex. Hemolysis assays have shown that the amphipathic peptide destabilizes lipid bilayers at low pH, mimicking the properties of viral fusogenic peptides. However, circular dichroism studies show that unlike the viral fusion peptides, this amphipathic peptide loses some of its alpha-helical structure at low pH in the presence of liposomes. The peptide-based gene delivery systems were tested for transfection efficiency in a variety of cell lines, including 14-day C2C12 mouse myotubes, using gene expression systems containing the beta-galactosidase reporter gene. Transfection data demonstrate a correlation between in vitro transfection efficiency and the combination of several physical properties of the peptide/plasmid complexes, including 1) DNA dose, 2) the zeta potential of the particle, 3) the requirement of both lytic and carrier peptides, and 4) the number of lysine residues associated with the carrier peptide. Transfection data on 14-day C2C12 myotubes utilizing the therapeutic human growth hormone gene formulated in an optimal peptide gene delivery system show an increase in gene expression over time, with a maximum in protein levels at 96 h (approximately 18 ng/ml).

Amino Acid Sequence↗
PubMed1998

Myocardial tissue engineering with autologous myoblast implantation.

OBJECTIVE: Implanting myoblasts derived from autologous skeletal muscle, that is, satellite cells, for myocardial replacement has many advantages when compared with implanting either fetal cardiac myocytes (ethical and donor availability issues) or established cell lines (oncogenicity). Furthermore, autologous myoblasts do not require immunosuppression. The feasibility of satellite cell differentiation into muscle fibers, after implantation into the myocardium, was confirmed by means of a unique cell-labeling technique. METHODS: Myoblasts (satellite cells) isolated from the skeletal muscle of adult rats are labeled with 4',6-diamidino-2-phenylindone, which binds to DNA and to the protein tubulin to form a fluorescent complex, and implanted into the left ventricular wall of isogenic rats. The specimens are harvested 1 to 4 weeks after myoblast implantation. Histologic sections are examined under a fluorescent microscope. RESULTS: The labeling efficiency of satellite cells with 4',6-diamidino-2-phenylindole is nearly 100%. In 4 specimens, the progressive differentiation of implanted myoblasts into fully developed striated muscle fibers can be observed. CONCLUSION: Our earlier studies of autologous myoblast implantation into the cryoinjured myocardium of dogs suggested that these cells could differentiate into cardiac myocytes. However, it had been difficult to firmly establish these findings with the use of cell markers, thereby proving that the neomyocardium had indeed been derived from the implanted myoblasts. In this study, using 4',6-diamidino-2-phenylindole as a satellite cell marker, we were able to demonstrate that the implanted satellite cells did in fact differentiate into fully developed, labeled muscle fibers. Because of the obvious advantages of using autologous donor myoblasts, the clinical application of this approach may provide a novel strategy for the future management of heart failure.

Animals↗
PubMed1998

Identification of H. pylori in saliva by a nested PCR assay derived from a newly cloned DNA probe.

A novel probe was developed from genomic DNA of Helicobacter pylori ATCC type strain 43629. It hybridized with all 73 H. pylori clinical isolates tested but not with any of 183 non-H. pylori DNAs in dot blot hybridization. Typing tests revealed 41 different HaeIII-digestion patterns from 57 H. pylori strains tested. Based on the sequence of the probe, a nested PCR was developed that detected as little as 2 fg of H. pylori DNA or approximately equivalent to one cell. No PCR products were amplified from any of 21 non-H. pylori strains tested. Using this nested PCR, H. pylori DNA was detected in 33 of 45 (73%) saliva samples collected from patients with gastric H. pylori infection. These data suggest that the probe is useful for typing H. pylori and that the nested PCR is a valuable tool for detecting H. pylori DNA in saliva.

DNA Fingerprinting↗
PubMed1998

Ethanol-induced inhibition of a neuronal P2X purinoceptor by an allosteric mechanism.

Ethanol inhibits a neuronal P2X purinoceptor by shifting the ATP concentration-response curve to the right in an apparently competitive manner. However, the underlying mechanism has not been determined. We investigated the effects of ethanol on the activation and deactivation time constants for ATP-activated current in bullfrog dorsal root ganglion neurones. Ethanol decreased the time constant of deactivation of ATP-gated ion channels without affecting the time constant of activation. The observations are not consistent with a competitive mechanism of inhibition by ethanol, but may be explained by an allosteric action of ethanol to decrease apparent agonist affinity. This represents a novel mechanism of action of ethanol on a neurotransmitter-gated ion channel.

Adenosine Triphosphate↗
PubMed1998

Inhibition of NMDA-gated ion channels by the P2 purinoceptor antagonists suramin and reactive blue 2 in mouse hippocampal neurones.

1. The action of suramin and reactive blue 2 on N-methyl-D-aspartate (NMDA)-activated ion current was studied in mouse hippocampal neurones in culture by use of whole-cell patch-clamp recording. 2. Suramin and reactive blue 2 inhibited steady-state current activated by 25 microM NMDA with IC50 values of 68 and 11 microM, respectively. 3. Reactive blue 2 produced a gradual decline of NMDA-activated current to a steady-state, but this slow onset was not an indication of use-dependence, as it could be eliminated by exposure to reactive blue 2 before NMDA application. In addition, NMDA-activated current recovered completely from inhibition by reactive blue 2 in the absence of agonist. 4. The slow onset of inhibition by reactive blue 2 was not apparently due to an action at an intracellular site, as inclusion of 250 microM reactive blue 2 in the recording pipette did not alter inhibition by 25 microM reactive blue 2 applied externally. 5. Reactive blue 2 and suramin inhibited NMDA-gated channels in a voltage-independent manner. 6. Reactive blue 2, 25 microM, decreased the maximal response to NMDA from 1441 to 598 pA without changing its EC50. In contrast, 75 microM suramin increased the EC50 for NMDA from 13 to 35 microM, and decreased the maximal response to NMDA from 1822 to 1498 pA. Schild analysis of suramin inhibition of NMDA-activated current yielded a nonlinear plot. 7. Both agents decreased the maximal response to glycine without altering its EC50. 8. Suramin and reactive blue 2 appear to inhibit NMDA receptor-channels in a manner that is noncompetitive with respect to both NMDA and glycine. However, inhibition by suramin differed from that by reactive blue 2, in that suramin significantly increased the EC50 of NMDA.

Animals↗
PubMed1998

Giant cell tumor of the sphenoid bone.

OBJECTIVE AND IMPORTANCE: Giant cell tumor of the sphenoid bone is extremely unusual. This tumor is usually located in long bones and is rarely located in the cranial vault. It must be differentiated from reparative granuloma and the Brown tumor of hyperparathyroidism. This case report is only the second involving a patient in the first decade. CLINICAL PRESENTATION: A 9-year-old girl presented with cephalgia and diplopia. Radiographic imaging revealed an erosive mass in the clivus. INTERVENTION: The patient underwent an extended transphenoidal resection of the clivus. This was followed with 57.6 CGE in 32 fractionated doses. CONCLUSION: At 1 year follow-up, the tumor remains stable. Based on anecdotal evidence, attempted resection with adjuvant radiation therapy allows for long-term survival in these patients.

Case Reports↗
PubMed1998

Recombinant pICln forms highly cation-selective channels when reconstituted into artificial and biological membranes.

pICln has been proposed to be the swelling-activated anion channel responsible for ICl, swell, or a channel regulator. We tested the anion channel hypothesis by reconstituting recombinant pICln into artificial and biological membranes. Single channels were observed when pICln was reconstituted into planar lipid bilayers. In the presence of symmetrical 300 mM KCl, the channels had a high open probability and a slope conductance of 48 pS, and were outwardly rectifying. Reduction of trans KCl to 50 mM shifted the reversal potential by -31.2 +/- 0.06 mV, demonstrating that the channel is at least seven times more selective for cations than for anions. Consistent with this finding, channel conductance was unaffected by substitution of Cl- with glutamate, but was undetectable when K+ was replaced by N-methyl-D-glucamine. Reconstitution of pICln into liposomes increased 86Rb+ uptake by three- to fourfold, but had no effect on 36Cl- uptake. Phosphorylation of pICln with casein kinase II or mutation of G54, G56, and G58 to alanine decreased channel open probability and 86Rb+ uptake. When added to the external medium bathing Sf9 cells, pICln inserted into the plasma membrane and increased cell cation permeability. Taken together, these observations demonstrate that channel activity is due to pICln and not minor contaminant proteins. However, these findings do not support the hypothesis that pICln is the anion-selective ICl, swell channel. The observed cation channel activity may reflect an as yet to be defined physiological function of pICln, or may be a consequence of in vitro reconstitution of purified, recombinant protein.

Animals↗
PubMed1998

Sex ratio associated with timing of insemination and length of the follicular phase in planned and unplanned pregnancies during use of natural family planning.

This was a multicentred, prospective study of pregnancies among women using natural family planning. The women maintained natural family planning charts of the conception cycle, recording acts of intercourse and signs of ovulation (cervical mucus changes, including peak day and basal body temperature). Charts were used to assess the most probable day of insemination relative to the day of ovulation and length of the follicular phase of the cycle. The sex ratio (males per 100 females) for 947 singleton births was 101.5, not significantly different from the expected value of 105. The sex ratio did not vary consistently or significantly with the estimated timing of insemination relative to the day of ovulation, with the estimated length of the follicular phase or with the planned or unplanned status of the pregnancy. Although these findings may be affected by imprecision of the data, the study suggests that manipulation of the timing of insemination during the cycle cannot be used to affect the sex of offspring.

Family Planning Services↗
PubMed1998

Dispersion of ventricular repolarization in the voltage domain.

Dispersion of ventricular repolarization, assessed as QT dispersion in the ECG or by multiple monophasic action potential (MAP) recordings, is defined as the difference between the earliest and latest repolarization. It is thus measured in the time domain. However, myocardial refractoriness is primarily a function of the membrane potential during phase 3 repolarization. The purpose of this study, therefore, was to measure dispersion of ventricular repolarization in the voltage domain and to study its relation to VF inducibility. To further validate this concept, the effect of chronic amiodarone treatment on the voltage dispersion were assessed. MAPs were recorded simultaneously at 10 epicardial and endocardial sites in isolated rabbit hearts, both under baseline conditions (n = 8) and after chronic amiodarone treatment (n = 8). Repolarization dispersion in the voltage domain was calculated as the difference between the highest and lowest repolarization level of all 10 MAPs at 10-ms steps, starting from the MAP plateau level to complete repolarization. Plotting these voltage differences along the time axis resulted in a dispersion curve, which rose during early repolarization, reached a peak during phase 3 repolarization, and thereafter declined toward zero. There was a close correlation between VF vulnerability in response to electrical field stimuli and the time during which voltage dispersion was maximal (r = 0.828, P < 0.0001). Amiodarone caused a right-ward shift of both the dispersion curve (P = 0.007) and VF vulnerability (P = 0.025), but did not change the magnitude nor the shape of the voltage dispersion curve and its relation to VF vulnerability. Repolarization dispersion in the voltage domain describes an alternate approach for evaluating the heterogeneity of ventricular repolarization and may help to characterize arrhythmia susceptibility under experimental conditions.

Action Potentials↗
PubMed1998

Fetal growth in the baboon during the second half of pregnancy.

The normal growth profile of critical fetal organs through the last third of gestation has not been documented in detail in human fetuses or the fetus of any nonhuman primate species. Recent epidemiological studies in human pregnancy suggest that fetal growth plays a major role in the programming of life-long health by modifying cardiovascular, pancreatic, brain, and liver growth. The present study aimed to produce a detailed database of individual organ growth in the fetal baboon in late gestation. Fetal organ weights were obtained from 43 baboon fetuses between 121 and 177 days of gestation. Various organs (brain, heart, kidney, femur, intestines, and spinal cord) showed no sign of slowed growth in late gestation while growth of others (lung, liver, stomach, and bladder) accelerated in late gestation. The fetal adrenal and thymus showed a decrease in growth rate over the final 20 and 10 days of gestation respectively. These observations provide a database that will permit analysis of factors responsible for regulation of normal and altered fetal organ development in this important experimental species.

Adrenal Glands↗
PubMed1998

Efficacy of trovafloxacin, a new quinolone antibiotic, in experimental staphylococcal endocarditis due to oxacillin-resistant strains.

Therapeutic options for severe infections caused by strains of oxacillin-resistant Staphylococcus aureus (ORSA) and coagulase-negative staphylococci (ORSE) are very limited. With the increasing resistance of such strains to aminoglycosides, rifampin, and currently available quinolone agents, as well as the recent documentation of increasing resistance of ORSA to vancomycin (VANCO), new treatment alternatives are imperative. The in vivo efficacy of trovafloxacin (TROVA), a new quinolone agent with excellent antistaphylococcal activity in vitro, against experimental endocarditis (IE) due to beta-lactamase-producing ORSA and ORSE strains (ORSA and ORSE IE) was evaluated. TROVA (25 mg/kg of body weight intravenously [i.v.] twice daily [b.i.d]) was compared to VANCO (20 mg/kg i.v. b.i.d.) and two regimens of ampicillin-sulbactam (AMP-SUL; 200 mg/kg intramuscularly [i.m.] three times a day [t.i.d.] and 20 mg/kg i.m. b.i.d.), with all agents given for 3 or 6 days. AMP-SUL was included as a comparative treatment regimen because of its proven efficacy against experimental ORSA and ORSE IE. For both ORSA and ORSE IE, TROVA, AMP-SUL, and VANCO each reduced staphylococcal densities in vegetations compared to untreated controls (P < 0.01). For ORSA IE, TROVA was the most rapidly bactericidal agent--although not to a statistically significant degree--correlating with its superior bactericidal effect in vitro compared to those of VANCO and AMP-SUL.

Animals↗
PubMed1998

A novel serine/threonine protein kinase homologue of Pseudomonas aeruginosa is specifically inducible within the host infection site and is required for full virulence in neutropenic mice.

A genetic locus of Pseudomonas aeruginosa was identified that is highly and specifically inducible during infection of neutropenic mice. This locus, ppkA, encodes a protein that is highly homologous to eukaryote-type serine/threonine protein kinases. A ppkA null mutant strain shows reduced virulence in neutropenic mice compared to the wild type. Overexpression of the PpkA protein greatly inhibited the growth of Escherichia coli or P. aeruginosa. However, a single amino acid change at the catalytic site of the kinase domain eliminated the toxic effect of PpkA on bacterial cells, suggesting that the kinase domain of PpkA is functional within bacterial cells.

Amino Acid Sequence↗
PubMed1998

Structure and expression of the FlaA periplasmic flagellar protein of Borrelia burgdorferi.

The spirochete which causes Lyme disease, Borrelia burgdorferi, has many features common to other spirochete species. Outermost is a membrane sheath, and within this sheath are the cell cylinder and periplasmic flagella (PFs). The PFs are subterminally attached to the cell cylinder and overlap in the center of the cell. Most descriptions of the B. burgdorferi flagellar filaments indicate that these organelles consist of only one flagellin protein (FlaB). In contrast, the PFs from other spirochete species are comprised of an outer layer of FlaA and a core of FlaB. We recently found that a flaA homolog was expressed in B. burgdorferi and that it mapped in a fla/che operon. These results led us to analyze the PFs and FlaA of B. burgdorferi in detail. Using Triton X-100 to remove the outer membrane and isolate the PFs, we found that the 38.0-kDa FlaA protein purified with the PFs in association with the 41.0-kDa FlaB protein. On the other hand, purifying the PFs by using Sarkosyl resulted in no FlaA in the isolated PFs. Sarkosyl has been used by others to purify B. burgdorferi PFs, and our results explain in part their failure to find FlaA. Unlike other spirochetes, B. burgdorferi FlaA was expressed at a lower level than FlaB. In characterizing FlaA, we found that it was posttranslationally modified by glycosylation, and thus it resembles its counterpart from Serpulina hyodysenteriae. We also tested if FlaA was synthesized in a spontaneously occurring PF mutant of B. burgdorferi (HB19Fla-). Although this mutant still synthesized flaA message in amounts similar to the wild-type amounts, it failed to synthesize FlaA protein. These results suggest that, in agreement with data found for FlaB and other spirochete flagellar proteins, FlaA is likely to be regulated on the translational level. Western blot analysis using Treponema pallidum anti-FlaA serum indicated that FlaA was antigenically well conserved in several spirochete species. Taken together, the results indicate that both FlaA and FlaB comprise the PFs of B. burgdorferi and that they are regulated differently from flagellin proteins of other bacteria.

Borrelia↗
PubMed1998

Even-skipped represses transcription by binding TATA binding protein and blocking the TFIID-TATA box interaction.

The Drosophila homeodomain protein Even-skipped (Eve) is a transcriptional repressor, and previous studies have suggested that it functions by interfering with the basal transcription machinery. Here we describe experiments indicating that the mechanism of Eve repression involves a direct interaction with the TATA binding protein (TBP) that blocks binding of TBP-TFIID to the promoter. We first compared Eve activities in in vitro transcription systems reconstituted with either all the general transcription factors or only TBP, TFIIB, TFIIF30, and RNA polymerase II. In each case, equivalent and very efficient levels of repression were observed, indicating that no factors other than those in the minimal system are required for repression. We then show that Eve can function efficiently when its recognition sites are far from the promoter and that the same regions of Eve required for repression in vivo are necessary and sufficient for in vitro repression. This includes, in addition to an Ala-Pro-rich region, residues within the homeodomain. Using GAL4-Eve fusion proteins, we demonstrate that the homeodomain plays a role in repression in addition to DNA binding, which is to facilitate interaction with TBP. Single-round transcription experiments indicate that Eve must function prior to TBP binding to the promoter, suggesting a mechanism whereby Eve represses by competing with the TATA box for TBP binding. Consistent with this, excess TATA box-containing oligonucleotide is shown to specifically and efficiently disrupt the TBP-Eve interaction. Importantly, we show that Eve binds directly to TFIID and that this interaction can also be disrupted by the TATA oligonucleotide. We conclude that Eve represses transcription via a direct interaction with TBP that blocks TFIID binding to the promoter.

Animals↗