Biomedical subjects

Mi Li

Publications and source records attributed to Mi Li.

25 records · Page 2Linked to original sources

PubMed2003

[The changes of angiotensin II receptor expression in cardiomyocytes of ventricles in pigs with experimental ventricular septal defect].

OBJECTIVE: To investigate the changes of angiotensin II receptors expression in cardiomyocytes of both ventricles in pigs with experimental ventricular septal defect (VSD). METHODS: Nineteen young pigs were divided into 3 groups: the pigs that received operation to produce experimental VSD, the pigs that underwent sham-operation, and the pigs as normal control. One month after the operation, the pigs were catheterized and then put to death; the cardiomyocytes were taken from their ventricles and were isolated. Radioligand binding assay was done to measure the Bmax and KD of angiotensin II receptor per 10(6) cells. RESULTS: For both Bmax and KD of angiotensin II receptors, there were no significant differences between the sham-operation group and the control. The Bmax of left ventricle AT1R (188.42 +/- 133.97 fmol/10(6)) and Bmax of right ventricle AT1R (272.14 +/- 232.74 fmol/10(6)) and AT2R (40.42 +/- 34.76 fmol/10(6)) in the operation group were significantly elevated in comparison with the control (Bmax of left ventricle AT1R 29.20 +/- 19.50 fmol/L, and Bmax of right ventricle AT1R 76.72 +/- 51.21 fmol/L and AT2R 9.63 +/- 1.27 fmol/L) respectively, P < 0.05. CONCLUSION: Intracardiac left-to-right shunt related volume overload leads to the elevation of AT1R expression in cardiomyocytes, which serves as an important mechanism of ventriclular hypertrophy and remodling in congenital heart disease. The increased expression of AT2R in right ventricle is a possible explanation of the phenomenon that moderately sized VSDs usually show left other than right ventriclular hypertrophy, taking into account that AT2R has been suggested to mediate antitrophic reaction.

Animals↗

PubMed2003

[Effect of truncated platelet-derived growth factor-alpha receptor on apoptosis and expression of c-sis mRNA of pulmonary artery smooth muscle cells].

OBJECTIVE: Platelet-derived growth factor (PDGF) plays an important role during the pathophysiological changes in vascular remodeling. The study aimed to investigate the effect of truncated PDGF-alpha receptor on apoptosis and expression of c-sis mRNA of pulmonary artery smooth muscle cells (VSMCs). METHODS: Tissue mass culture was done to get vascular smooth muscle cells of pulmonary artery in newborn pigs. Two methods were used to interfere VSMCs: adding adenoviral recombined body (Ad5CMV-PalphaRtr, ACP) with three different concentrations of truncated PDGF-alpha receptor into the cultures, or adding three concentrations of PDGF-BB after the treatment with mid-concentration of ACP. VSMC apoptosis, cellular cycle and expression of c-sis were observed using flow-cytometry, and the expression of c-sis mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR). RESULTS: ACP with mid- to- high concentrations could restrain the proliferation of VSMCs apparently with the increase of G(0)/G(1) cells. The apoptotic rate presented an ascending tendency. The differences among the groups were of statistically significant. Affected by mid- concentration of ACP, PDGF-BB did not exhibit a significantly accelerating effect on the changes of cellular cycle and VSMC apoptosis. The expression of c-sis mRNA was up-regulated under the effect of ACP. Affected by mid-concentration of ACP and PDGF-BB, c-sis mRNA expressed was down-regulated. CONCLUSION: Mid- to- high concentration of ACP is a powerful inhibitor of cellular proliferation for pulmonary artery VSMCs. It can significantly increase cells in number in G(0)/G(1) phase, apoptosis and c-sis mRNA expression.

Animals↗

PubMed2002

Structural basis for the substrate specificity of tobacco etch virus protease.

Because of its stringent sequence specificity, the 3C-type protease from tobacco etch virus (TEV) is frequently used to remove affinity tags from recombinant proteins. It is unclear, however, exactly how TEV protease recognizes its substrates with such high selectivity. The crystal structures of two TEV protease mutants, inactive C151A and autolysis-resistant S219D, have now been solved at 2.2- and 1.8-A resolution as complexes with a substrate and product peptide, respectively. The enzyme does not appear to have been perturbed by the mutations in either structure, and the modes of binding of the product and substrate are virtually identical. Analysis of the protein-ligand interactions helps to delineate the structural determinants of substrate specificity and provides guidance for reengineering the enzyme to further improve its utility for biotechnological applications.

Amino Acid Sequence↗

PubMed2002

The discrimination of drug mixtures using a four-choice procedure in pigeons.

RATIONALE: The purpose of these experiments was to study drug combinations as discriminative stimuli using a new four-choice procedure. OBJECTIVES: To determine whether pigeons could discriminate among a mixture of two drugs, each of the component drugs and saline, and to study other drug combinations in these birds. METHODS: Pigeons were trained to discriminate among saline, 5 mg/kg morphine, 5 mg/kg pentobarbital, and a mixture of these two doses using a four-choice procedure. RESULTS: When responding stabilized, the birds responded on the correct key more than 90% of the time. Low doses of all drugs given alone produced responding on the saline key. Higher doses of pentobarbital and chlordiazepoxide produced responding on the pentobarbital key, and higher doses of morphine produced responses on the morphine key. Methamphetamine produced responding on the saline key. None of the drugs given alone produced responding on the mixture key. When pentobarbital was combined with morphine, doses both below and above the combined training doses of these drugs usually produced responding on the mixture key. The combination of chlordiazepoxide with morphine produced similar results. Combinations of methamphetamine with pentobarbital or with morphine produced effects similar to those of pentobarbital or morphine given alone. CONCLUSIONS: A wide range of combinations of pentobarbital and morphine, or chlordiazepoxide and morphine produce responding on the mixture key, even though the pigeons were not exposed to these dose combinations during training. The four-choice procedure provides the opportunity to study drug mixtures in a detail not possible with more limited response choices.

Animals↗

PubMed2002

An unusual orientation for Tyr75 in the active site of the aspartic proteinase from Saccharomyces cerevisiae.

The structures of the native Saccharomyces cerevisiae proteinase A have been solved by molecular replacement in the monoclinic and trigonal crystal forms and refined at 2.6-2.7A resolution. These structures agree overall with those of other uninhibited aspartic proteinases. However, an unusual orientation for the side chain of Tyr75, a conserved residue on the flexible "flap" that covers the active site and is important for the activity of these enzymes, was found in the trigonal crystals. A similar conformation of Tyr75 occupying the S1 substrate-binding pocket was previously reported only for chymosin (where it was interpreted as representing a "self-inhibited" state of the enzyme), but for no other aspartic proteinases. Since this orientation of Tyr75 has now been seen in the structures of two members of the family of aspartic proteinases, it might indicate that the placement of that residue in the S1 substrate-binding pocket might have some functional significance, analogous to what was seen for self-inhibited structures of serine proteinases.

Aspartic Acid Endopeptidases↗

PubMed2002

Pharmacokinetic antagonism of (+)-methamphetamine discrimination by a low-affinity monoclonal anti-methamphetamine antibody.

Animals were trained to discriminate 5 or 10 mg/kg cocaine (rats), or 3 mg/kg (+)-amphetamine (pigeons) from saline, after which dose-response curves were determined for (+)-methamphetamine and other drugs before and after administration of a (+)-methamphetamine-specific monoclonal antibody (K(D) =250 nM). In rats trained to discriminate 10 mg/kg cocaine from saline, intravenous (+)-methamphetamine was about three times more potent as a discriminative stimulus than intraperitoneal (+)-methamphetamine. Also in these rats, intraperitoneal (+)-methamphetamine and (+)-amphetamine were about equipotent as discriminative stimuli, and were about three times more potent than intraperitoneal cocaine. In pigeons trained to discriminate 3 mg/kg intramuscular (i.m.) (+)-amphetamine from saline, (+)-methamphetamine and (+)-amphetamine were nearly equipotent, while cocaine was slightly less potent. In rats trained to discriminate 5 or 10 mg/kg cocaine from saline, intravenous administration of 1 g/kg of the antibody shifted both intravenous and intraperitoneal dose-response curves for (+)-methamphetamine discrimination approximately threefold to the right at 1 or 4 days after administration of the antibody. In pigeons trained to discriminate 3 mg/kg intramuscular (+)-amphetamine from saline, a similar shift of the (+)-methamphetamine dose-response curve to the right also lasted for 4-7 days. However, the antibody did not affect the (+)-amphetamine dose-response curve (pigeons), or the cocaine (rats) dose-response curve. The data show that a low affinity anti-(+)-methamphetamine-specific antibody can produce a specific antagonism of an effect of (+)-methamphetamine that is closely associated with its abuse.

Animals↗

PubMed2002

Drug discrimination under concurrent variable-ratio variable-ratio schedules.

Pigeons were trained to discriminate 5 mg/kg pentobarbital from saline under concurrent variable-ratio (VR) VR schedules, in which responses on the pentobarbital-biased lever were reinforced under the VR schedule with the smaller response requirements when pentobarbital was given before the session, and responses on the saline-biased key were reinforced under the VR schedule with the larger response requirements. When saline was administered before the session, the reinforcement contingencies associated with the two response keys were reversed. When responding stabilized under concurrent VR 20 VR 30, concurrent VR 10 VR 40, or concurrent VR 5 VR 50 schedules, pigeons responded almost exclusively on the key on which fewer responses were required to produce the reinforcer. When other doses of pentobarbital and other drugs were substituted for the training dose, low doses of all drugs produced responding on the saline-biased key. Higher doses of pentobarbital and chlordiazepoxide produced responding only on the pentobarbital-biased key, whereas higher doses of ethanol and phencyclidine produced responding only on this key less often. d-Amphetamine produced responding primarily on the saline-biased key. When drugs generalized to pentobarbital, the shape of the generalization curve under concurrent VR VR schedules was more often graded than quantal in shape. Thus, drug discrimination can be established under concurrent VR VR schedules, but the shapes of drug-discrimination dose-response curves under concurrent VR VR schedules more closely resemble those seen under interval schedules than those seen under fixed-ratio schedules. Graded dose-response curves under concurrent VR VR schedules may relate to probability matching and difficulty in discriminating differences in reinforcement frequency.

Animals↗