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H Li

Publications and source records attributed to H Li.

At least 775 records · Page 43Linked to original sources
PubMed1999

Attenuation of the slow component of delayed rectification, action potential prolongation, and triggered activity in mice expressing a dominant-negative Kv2 alpha subunit.

An in vivo experimental strategy, involving cardiac-specific expression of a mutant Kv 2.1 subunit that functions as a dominant negative, was exploited in studies focused on exploring the role of members of the Kv2 subfamily of pore-forming (alpha) subunits in the generation of functional voltage-gated K(+) channels in the mammalian heart. A mutant Kv2.1 alpha subunit (Kv2.1N216) was designed to produce a truncated protein containing the intracellular N terminus, the S1 membrane-spanning domain, and a portion of the S1/S2 loop. The truncated Kv2.1N216 was epitope tagged at the C terminus with the 8-amino acid FLAG peptide to generate Kv2. 1N216FLAG. No ionic currents are detected on expression of Kv2. 1N216FLAG in HEK-293 cells, although coexpression of this construct with wild-type Kv2.1 markedly reduced the amplitudes of Kv2. 1-induced currents. Using the alpha-myosin heavy chain promoter to direct cardiac specific expression of the transgene, 2 lines of Kv2. 1N216FLAG-expressing transgenic mice were generated. Electrophysiological recordings from ventricular myocytes isolated from these animals revealed that I(K, slow) is selectively reduced. The attenuation of I(K, slow) is accompanied by marked action potential prolongation, and, occasionally, spontaneous triggered activity (apparently induced by early afterdepolarizations) is observed. The time constant of inactivation of I(K, slow) in Kv2. 1N216FLAG-expressing cells (mean+/-SEM=830+/-103 ms; n=17) is accelerated compared with the time constant of I(K, slow) inactivation (mean+/-SEM=1147+/-57 ms; n=25) in nontransgenic cells. In addition, unlike I(K, slow) in wild-type cells, the component of I(K, slow) remaining in the Kv2.1N216FLAG-expressing cells is insensitive to 25 mmol/L tetraethylammonium. Taken together, these observations suggest that there are 2 distinct components of I(K, slow) in mouse ventricular myocytes and that Kv2 alpha subunits underlie the more slowly inactivating, tetraethylammonium-sensitive component of I(K, slow). In vivo telemetric recordings also reveal marked QT prolongation, consistent with a defect in ventricular repolarization, in Kv2.1N216FLAG-expressing transgenic mice.

Action Potentials↗
PubMed1999

Frequency of noncontiguous lymph node involvement in patients with resectable nonsmall cell lung carcinoma.

BACKGROUND: This study was undertaken to investigate the patterns of lymph node spread and the frequency of involvement of noncontiguous lymph node stations in patients with nonsmall cell lung carcinoma who had complete surgical resection. METHODS: All patients who had surgical resection as their sole treatment for nonsmall cell lung carcinoma during the years 1987-1990 were reviewed. All patients were treated similarly. Generally, complete mediastinal lymph node dissection was performed after resection of the primary lesion and N1 lymph nodes. Patients were assessed for patterns of involvement of N1 and N2 lymph node stations. The frequency of noncontiguous involvement of lymph nodes (involvement of N2 lymph nodes without involvement of N1 lymph nodes) was determined. Patient and tumor characteristics were assessed to ascertain whether certain factors were likely to predict this noncontiguous pattern of lymph node spread. RESULTS: During the 4-year period of study, 336 patients with nonsmall cell lung carcinoma were managed with surgical resection alone. Of the 336, 100 had no involvement of lymph nodes, 108 had involvement of N1 lymph nodes only, 76 had involvement of N1 and N2 lymph nodes, and 52 had involvement of N2 lymph nodes only. Therefore, 52 of all 336 patients (15%) and 52 of 236 patients with lymph node involvement (22%) had noncontiguous lymph node spread. A review of the initial patient and tumor characteristics revealed that patients with a suggestion of enlarged mediastinal lymph nodes on preoperative computed tomography scans of the chest (compared with negative findings) and patients with T1 and T2 lesions (compared with T3 and T4) were more likely to have noncontiguous lymph node spread; the odds ratios (with 95% confidence intervals) were 2.18 (1.01-4.71) and 2.82 (1.36-5.84), respectively. CONCLUSIONS: Noncontiguous involvement of thoracic lymph nodes occurred in approximately 15% of patients who had complete surgical resection of nonsmall cell lung carcinoma. This factor suggests that lack of involvement of N1 lymph nodes does not rule out mediastinal involvement and provides important information for complete surgical staging.

Carcinoma, Non-Small-Cell Lung↗
PubMed1999

Local circuit neurons showing calbindin D28k-immunoreactivity in the substantia gelatinosa of the medullary dorsal horn of the rat. An immunohistochemical study combined with intracellular staining in slice preparation.

Calbindin D28k (CB)-immunoreactive local circuit neurons in the substantia gelatinosa of the rat medullary dorsal horn were studied in slice preparations; intracellular injection of biocytin was followed by histochemical visualization of biocytin, then CB immunohistochemistry was performed. In six neurons so far examined, overall morphology, including those of dendritic fields, axonal fields, and arborization patterns, was common.

Animals↗
PubMed1999

Patients with stage I non-small cell lung carcinoma at postoperative risk for local recurrence, distant metastasis, and death: implications related to the design of clinical trials.

PURPOSE: Patients with pathologically staged American Joint Committee on Cancer stage I (T1 N0 or T2 N0) non-small cell lung cancer have a favorable prognosis after complete surgical resection compared with patients with more advanced stages. Benefits of adjuvant therapy in this setting are unproved. However, there may be subgroups of patients with stage I disease at high enough risk for local recurrence to prompt consideration of adjuvant or neoadjuvant radiation therapy. Likewise, there may be subgroups of patients at high enough risk for distant metastasis to justify the evaluation of chemotherapy. METHODS AND MATERIALS: From 1987 through 1990, 370 patients undergoing gross total resection of non-small cell lung cancer had stage I disease and received no chemotherapy or radiation therapy as part of their primary treatment. These patients were the subject of a retrospective review to separate patients into high-, intermediate-, and low-risk groups with respect to freedom from local recurrence (FFLR), freedom from distant metastasis (FFDM), and overall survival by using a regression tree analysis. RESULTS: The 5-year rates of FFLR, FFDM, and survival were 85%, 83%, and 66%, respectively. Regression analyses revealed that the factors independently predicting for a poorer FFLR rate included fewer than 15 lymph nodes dissected and pathologically evaluated (p = 0.002) and the presence of a T2 tumor (p = 0.04). Factors independently predicting for a poorer FFDM rate included a maximal dimension greater than 5 cm (p = 0.02) and nonsquamous histology (p = 0.03). Factors independently predicting for a poorer survival rate included fewer than 15 lymph nodes dissected and pathologically evaluated p = 0.001) and a maximal dimension greater than 3 cm (p = 0.003). Regression tree analyses were used to separate patients into risk groups. CONCLUSION: Incorporating the aforementioned factors into regression tree analyses, three risk groups were identified with respect to FFLR. Two each were identified for FFDM and for survival. For each of these three end-points, the differences in outcomes for each risk group were found to be both statistically and clinically significant. These risk groups may be useful in the future design of phase III trials evaluating the use of adjuvant chemotherapy and radiation therapy in the stage I setting.

Carcinoma, Non-Small-Cell Lung↗
PubMed1999

Substantia gelatinosa neurons in the medullary dorsal horn: An intracellular labeling study in the rat.

Morphologic features and electrical membrane properties of neurons in the substantia gelatinosa (SG) of the caudal spinal trigeminal nucleus (the medullary dorsal horn; MDH) were examined in the rat. Intracellular recording and biocytin-injection combined with histochemical staining were performed in horizontal slices. Twenty-four SG (lamina II) neurons were recorded stably and stained successfully. Both projection neurons (PNs; n = 9) that sent axons to regions outside the MDH and intrinsic neurons (INs; n = 15) that sent axons only to the MDH were observed. The INs were divided into those with dense axonal arborization (INDAs; n = 7) and those with sparse axonal arborization (INSAs; n = 8). In the PNs, the dendrites with spines spread to all MDH layers (laminae I-III). The main axons sent collaterals within the SG and rostrally, caudally, or medially to laminae I and III of the MDH, interpolar spinal trigeminal nucleus, spinal tract of the trigeminal nerve, or upper cervical cord segments. In the INDAs, the dendrites arising from the rostral and caudal pole of the cell bodies mainly extended rostrally and caudally parallel to the rostrocaudal axis of the SG: the dendritic trees were elongated and oval in shape and were confined within the SG. The axonal field of each INDA, a dense mesh of axonal processes, was elongated and oval in shape and almost was confined within the SG. In the INSAs, a small, round cell body was located in the center of each dendritic field, which usually was limited within the SG. Axonal processes ran radially to spread to all layers of the MDH, constituting round or oval axonal fields. The three groups of SG neurons showed more or less different intracellular responses to current injections. In particular, adaptation of spike frequency, hyperpolarizing sag, and rebound excitation were observed in the PNs and INSAs but not in the INDAs. Slow ramp depolarization and slow afterdepolarization were recorded only in INDAs.

Action Potentials↗
PubMed1999

Notch signalling controls pancreatic cell differentiation.

The pancreas contains both exocrine and endocrine cells, but the molecular mechanisms controlling the differentiation of these cell types are largely unknown. Despite their endodermal origin, pancreatic endocrine cells share several molecular characteristics with neurons, and, like neurons in the central nervous system, differentiating endocrine cells in the pancreas appear in a scattered fashion within a field of progenitor cells. This indicates that they may be generated by lateral specification through Notch signalling. Here, to test this idea, we analysed pancreas development in mice genetically altered at several steps in the Notch signalling pathway. Mice deficient for Delta-like gene 1 (Dll1) or the intracellular mediator RBP-Jkappa showed accelerated differentiation of pancreatic endocrine cells. A similar phenotype was observed in mice over-expressing neurogenin 3 (ngn 3) or the intracellular form of Notch3 (a repressor of Notch signalling). These data provide evidence that ngn3 acts as proendocrine gene and that Notch signalling is critical for the decision between the endocrine and progenitor/exocrine fates in the developing pancreas.

Animals↗
PubMed1999

Elimination of the transient outward current and action potential prolongation in mouse atrial myocytes expressing a dominant negative Kv4 alpha subunit.

1. Analyses of whole-cell voltage-clamp recordings from isolated adult (C57BL6) mouse atrial myocytes reveal the presence of two prominent Ca2+-independent depolarization-activated K+ currents: a rapidly activating and inactivating, transient outward K+ current, Ito,f; and a non-inactivating, steady-state, K+ current, Iss. 2. The properties of Ito,f and Iss in adult mouse atrial myocytes are similar to those of the analogous currents recently described in detail in adult mouse ventricular cells. A slowly inactivating K+ current, which is similar to IK,slow in ventricular cells, is detected in approximately 40 % of adult mouse atrial myocytes, and when expressed, the density of this current component is substantially lower than the density of Ito,f or Iss. 3. The similarity between atrial and ventricular Ito,f and the finding that both the Kv4 subfamily alpha subunits, Kv4.2 and Kv4.3, are expressed in wild-type mouse atria prompted us to determine if atrial Ito,f is affected in transgenic mice expressing a mutant Kv4. 2 alpha subunit, Kv4.2W362F, that functions as a dominant negative. 4. Similar to findings in ventricular cells, electrophysiological recordings reveal that Ito,f is selectively eliminated in atrial myocytes isolated from transgenic mice expressing Kv4.2W362F, thereby demonstrating directly that Kv4 subfamily members also underlie mouse atrial Ito,f. 5. Neither the steady-state, non-inactivating K+ current Iss, nor the inwardly rectifying K+ current IK1, in atrial myocytes is affected by the expression of Kv4. 2W362F.6 In contrast to previous findings in Kv4.2W362F-expressing mouse ventricular myocytes, there is no evidence that electrical remodelling occurs in atrial cells when Ito,f is functionally eliminated. 6. The elimination of Ito,f is accompanied by marked increases in atrial action potential durations, although no electrocardiographic abnormalities attributable to, or suggestive of, altered atrial functioning are evident in Kv4.2W362F-expressing animals.

Action Potentials↗
PubMed1999

Purification and characterization of an RNA dodecamer sequence binding protein from mitochondria of Saccharomyces cerevisiae.

Saccharomyces cerevisiae mitochondrial mRNAs terminate at their 3' ends with a conserved dodecamer sequence, 5'-AAUAA(U/C)AUUCUU-3'. We have identified a nuclear-encoded protein (DBP) which specifically binds to the dodecamer sequence and have purified it to apparent homogeneity by RNA affinity chromatography. DBP consists of a single polypeptide of 55 kDa and binds to its RNA substrate with a 1:1 stoichiometry. Scatchard analysis determines that K(d) is 0.93 nM for the canonical dodecamer sequence (5'-AAUAAUAUUCUU-3') and 0.46 nM for the only naturally occurring variant (5'-AAUAACAUUCUU-3') unique to oli1 gene. Based on the studies using mutant oligonucleotides, DBP appears to recognize primarily the nucleotide sequence of an RNA rather than its potential secondary structure.

Base Sequence↗
PubMed1999

Role of glutamate 91 in information transfer during substrate activation of yeast pyruvate decarboxylase.

Oligonucleotide-directed site-specific mutagenesis was carried out on pyruvate decarboxylase (EC 4.1.1.1) from Saccharomyces cerevisiae at E91, located on the putative substrate activation pathway and linking the alpha and gamma domains of the enzyme. While C221 on the beta domain is the residue at which substrate activation is triggered [Baburina, I., et al. (1994) Biochemistry 33, 5630-5635; Baburina, I., et al. (1996) Biochemistry 35, 10249-10255], that information, via the substrate bound at C221, is transmitted to H92 on the alpha domain, across the domain divide from C221 [Baburina, I. , et al. (1998) Biochemistry 37, 1235-1244], thence to E91 on the alpha domain, and then on to W412 on the gamma domain [Li, H., and Jordan, F. (1999) Biochemistry 38, 10004-10012] and to the active site thiamin diphosphate located at the interface of the alpha and gamma domains [Arjunan, D., et al. (1996) J. Mol. Biol. 256, 590-600]. Substitution at E91 with Q, D, or A led to modest reductions in the specific activity (4-, 5-, and 30-fold), as well as in both the turnover number and the catalytic efficiency, in that order. Interestingly, the Hill coefficient was only slightly reduced for the E91D variant, but cooperativity was virtually abolished for the E91Q and E91A variants. The thermal stability of the variants was reduced in the following order: wild type > E91Q > E91D > E91A; circular dichroism and fluorescence experiments also demonstrated that the tertiary structure of the enzyme was affected by these substitutions. The variants could be purified as apoenzymes, demonstrating their impaired ability to bind thiamin diphosphate. Apparently, the charge at residue 91 is quite important for maintaining optimal cooperativity. To maintain strong domain-domain interactions, the length of the side chain at position 91 with hydrogen bonding potential to W412 is sufficient.

Amino Acid Substitution↗
PubMed1999

Effects of substitution of tryptophan 412 in the substrate activation pathway of yeast pyruvate decarboxylase.

Oligonucleotide-directed site-specific mutagenesis was carried out on pyruvate decarboxylase (EC 4.1.1.1) from Saccharomyces cerevisiae at W412, located on the putative substrate activation pathway and linking E91 on the alpha domain with W412 on the gamma domain of the enzyme. While C221 on the beta domain is the residue at which substrate activation is triggered [Baburina, I., et al. (1994) Biochemistry 33, 5630-5635; Baburina, I., et al. (1996) Biochemistry 35, 10249-10255], that information, via the substrate bound at C221, is transmitted to H92 on the alpha domain, across the domain divide from C221 [Baburina, I., et al. (1998) Biochemistry 37, 1235-1244; Baburina, I., et al. (1998) Biochemistry 37, 1245-1255], thence to E91 on the alpha domain [Li, H., and Jordan, F. (1999) Biochemistry 38, 9992-10003], and then on to W412 on the gamma domain and to the active site thiamin diphosphate located at the interface of the alpha and gamma domains [Arjunan, D., et al. (1996) J. Mol. Biol. 256, 590-600]. Substitution at W412 with F and A was carried out, resulting in active enzymes with specific activities about 4- and 10-fold lower than that of the wild-type enzyme. Even though W412 interacts with E91 and H115 via a main chain hydrogen bond donor and acceptor, respectively, there is clear evidence for the importance of the indole side chain of W412 from a variety of experiments: thermostability, fluorescence quenching, and the binding constants of the thiamin diphosphate, and circular dichroism spectroscopy, in addition to conventional steady-state kinetic measurements. While the substrate activation is still prominent in the W412F variant, its level is very much reduced in the W412A variant, signaling that the size of the side chain is also important in positioning the amino acids surrounding the active center to achieve substrate activation. The fluorescence studies demonstrate that W412 is a relatively minor contributor to the well-documented fluorescence of apopyruvate decarboxylase in its native state. The information about the W412 variants provides strong additional support for the putative substrate activation pathway from C221 --> H92 --> E91 --> W412 --> G413 --> thiamin diphosphate. The accumulating evidence for the central role of the beta domain in stabilizing the overall structure is summarized.

Alanine↗
PubMed1999

Patterns of failure and overall survival in patients with completely resected T3 N0 M0 non-small cell lung cancer.

BACKGROUND: Previous studies of patients with surgically resected non-small cell lung cancer and chest wall invasion have shown conflicting results with respect to prognosis. Whether high-risk subsets of the T3 N0 M0 population exist with respect to patterns of failure and overall survival has been difficult to ascertain, owing to small numbers of patients in most series. METHODS AND MATERIALS: A retrospective review was performed to determine patterns of failure and overall survival for patients with completely resected T3 N0 M0 non-small cell lung cancer. From 1979 to 1993, 92 evaluable patients underwent complete resection for T3 N0 M0 non-small cell lung cancer. The following potential prognostic factors were recorded from the history: tumor size, location, grade, histology, patient age, use of adjuvant radiation therapy (18 of 92 patients), and type of surgical procedure (chest wall or extrapleural resection). RESULTS: The actuarial 2- and 4-year overall survival rates for the entire cohort were 48% and 35%, respectively. The actuarial local control at 4 years was 94%. Neither the type of surgical procedure performed nor the addition of thoracic radiation therapy impacted local control or overall survival. CONCLUSION: Patients with completely resected T3 N0 M0 non-small cell lung cancer have similar local control and overall survival irrespective of primary location, type of surgery performed, or use of adjuvant radiation therapy. Additionally, the tumor recurrence rate and overall survival found in this study support the placement of this group of patients in Stage IIB of the 1997 AJCC lung staging classification.

Carcinoma, Non-Small-Cell Lung↗
PubMed1999

Synthesis, characterization and the effect of ligand planarity of [Ru(bpy)2L]2+ on DNA binding affinity.

Two structurally related ligands (L) 4,5,9,18-tetraazaphenanthreno[9,10-b] triphenylene (taptp) and 2,3-diphenyl-1,4,8,9-tetraazatriphenylene (dptatp), and their related complexes of [Ru(bpy)2L]2+ have been synthesized and characterized by elemental analyses, 1H NMR and mass spectra. Their electrochemical properties were also examined. Both complexes emit intense luminescence in organic solvent but are quenched in water to different extents. The interactions of the complexes with calf thymus DNA have been investigated by viscosity, absorption, emission and circular dichroism spectra. The intrinsic binding constants of [Ru(bpy)2(taptp)]2+ and [Ru(bpy)2(dptatp)]2+ are 1.7 x 10(5) and 3.8 x 10(4) M-1, respectively. All data indicate that both complexes bind enantioselectively to double-stranded calf thymus DNA via the intercalative mode, with stronger affinity for the fully planar ligand complex of [Ru(bpy)2(taptp)]2+.

2,2'-Dipyridyl↗
PubMed1999

Crystal structures of zinc-free and -bound heme domain of human inducible nitric-oxide synthase. Implications for dimer stability and comparison with endothelial nitric-oxide synthase.

The crystal structures of the heme domain of human inducible nitric-oxide synthase (NOS-2) in zinc-free and -bound states have been solved. In the zinc-free structure, two symmetry-related cysteine residues form a disulfide bond. In the zinc-bound state, these same two cysteine residues form part of a zinc-tetrathiolate (ZnS(4)) center indistinguishable from that observed in the endothelial isoform (NOS-3). As in NOS-3, ZnS(4) plays a key role in stabilizing intersubunit contacts and in maintaining the integrity of the cofactor (tetrahydrobiopterin) binding site of NOS-2. A comparison of NOS-2 and NOS-3 structures illustrates the conservation of quaternary structure, tertiary topology, and substrate and cofactor binding sites, in addition to providing insights on isoform-specific inhibitor design. The structural comparison also reveals that pterin binding does not preferentially stabilize the dimer interface of NOS-2 over NOS-3.

Dimerization↗
PubMed1999

Patterns of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 expression in rabbit and mouse atherosclerotic lesions and at sites predisposed to lesion formation.

The recruitment of mononuclear leukocytes and formation of intimal macrophage-rich lesions at specific sites of the arterial tree are key events in atherogenesis. Inducible endothelial cell adhesion molecules may participate in this process. In aortas of normal chow-fed wild-type mice and rabbits, vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1), but not E-selectin, were expressed by endothelial cells in regions predisposed to atherosclerotic lesion formation. En face confocal microscopy of the mouse ascending aorta and proximal arch demonstrated that VCAM-1 expression was increased on the endothelial cell surface in lesion-prone areas. ICAM-1 expression extended into areas protected from lesion formation. Hypercholesterolemia induced atherosclerotic lesion formation in rabbits, LDL receptor and apolipoprotein E knockout mice, and Northern blot analysis demonstrated increased steady-state mRNA levels of VCAM-1 and ICAM-1, but not of E-selectin. Immunohistochemical staining revealed that VCAM-1 and ICAM-1 were expressed predominantly by endothelium in early lesions and by intimal cells in more advanced lesions. In early and advanced lesions, staining was most intense in endothelial cells at and adjacent to lesion borders. ICAM-1 staining extended into the uninvolved aorta. These expression patterns were highly reproducible in both species. The only difference was that VCAM-1 expression in endothelium over the central portions of lesions was found frequently in rabbits and rarely in mice. The expression of VCAM-1 by arterial endothelium in normal animals may represent a pathogenic mechanism or a phenotypic marker of predisposition to atherogenesis.

Animals↗
PubMed1999

3-(Diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one (DEPBT): a new coupling reagent with remarkable resistance to racemization.

[formula: see text] The new crystalline phosphate reagent 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one (DEPBT) mediates amide bond formation with a remarkable resistance to racemization. Comparative racemization studies were carried out and DEPBT proved to be superior to typical phosphonium and uronium coupling reagents. DEPBT is easily prepared and is exceedingly stable with a shelf life of months at room temperature. The advantageous properties of DEPBT render it a useful and unique addition to the arsenal of coupling reagents.

Amides↗
PubMed1999

Atomic levers control pyranose ring conformations.

Atomic force microscope manipulations of single polysaccharide molecules have recently expanded conformational chemistry to include force-driven transitions between the chair and boat conformers of the pyranose ring structure. We now expand these observations to include chair inversion, a common phenomenon in the conformational chemistry of six-membered ring molecules. We demonstrate that by stretching single pectin molecules (1 --> 4-linked alpha-D-galactouronic acid polymer), we could change the pyranose ring conformation from a chair to a boat and then to an inverted chair in a clearly resolved two-step conversion: 4C1 right arrow over left arrow boat right arrow over left arrow 1C4. The two-step extension of the distance between the glycosidic oxygen atoms O1 and O4 determined by atomic force microscope manipulations is corroborated by ab initio calculations of the increase in length of the residue vector O1O4 on chair inversion. We postulate that this conformational change results from the torque generated by the glycosidic bonds when a force is applied to the pectin molecule. Hence, the glycosidic bonds act as mechanical levers, driving the conformational transitions of the pyranose ring. When the glycosidic bonds are equatorial (e), the torque is zero, causing no conformational change. However, when the glycosidic bond is axial (a), torque is generated, causing a rotation around C---C bonds and a conformational change. This hypothesis readily predicts the number of transitions observed in pyranose monomers with 1a-4a linkages (two), 1a-4e (one), and 1e-4e (none). Our results demonstrate single-molecule mechanochemistry with the capability of resolving complex conformational transitions.

Carbohydrate Conformation↗