Search PubMed⌕ Search

Biomedical subjects

C Zhang

Publications and source records attributed to C Zhang.

At least 667 records · Page 37Linked to original sources
PubMed1994

Effects of basic fibroblast growth factor in retinal ischemia.

PURPOSE: Basic fibroblast growth factor (bFGF), a 17- to 24-kDa protein known to be essential for the survival of neurons, induced fiber outgrowth of ganglion cells in cultures of rat retina and rescued photoreceptor cell loss in the retina of Royal College of Surgeon rats. The authors evaluated the efficacy of bFGF in rescuing the neuronal loss in rat retina after retinal ischemia. METHODS: Retinal ischemia was induced in 29 eyes of 17 albino Lewis rats by increasing the intraocular pressure to 110 mm Hg for 45 minutes via an intracameral catheter. A total of 800 ng of bFGF was delivered into the anterior chamber at the time of induction of ischemia. Sixteen eyes of nine rats received bFGF, and 13 eyes of eight rats received heparin in phosphate-buffered saline as vehicle control. The animals were euthanized 7 or 14 days after reperfusion. RESULTS: Morphologic examination of the retinas at both time points showed that necrosis of the retinal ganglion cells (RGCs) and thinning of the inner plexiform and inner nuclear layers were less severe in the bFGF-treated eyes than in the vehicle-treated eyes. On morphometric examination, 7 days after reperfusion, the mean thickness of the inner retinal layers and the RGC counts on flat preparations of retina in both the posterior and the peripheral portions of the retina were significantly higher in the bFGF-treated eyes than in the vehicle-treated eyes (P < 0.02). At 14 days, similar beneficial effects were noted in all morphometric parameters, except RGC counts in the posterior pole. CONCLUSIONS: These results demonstrate that bFGF partially protects the RGCs and other inner retinal elements from ischemic injury.

Animals↗
PubMed1994

[Synaptonemal complex analysis of 13/17 Robertsonian translocation in the domestic pig].

G and C-banding study of the chromosomes of several male pigs, indicate that all of these pigs carry rob(13;17). The karyotype is 2n = 37, XY, rob (13;17). In this paper, silverstained Synaptonemal Complexes (SCs) in surface-spread pachytene nuclei from these pigs are analysed by electron microscope. The result is as follows: Robertsonian translocation metacentrics rob (13;17) paired with homologous acrocentrics (13,17), forming a trivalent. All trivalents are in a cis configuration and there is delayed pairing in the trivalent. We measured every part of trivalent in the different stage of prophase (based on the morphology of XY-bivalent). It is shown that accompanying with rob(13;17) formation there has been a deletion in the proximal part of 13, 17 translocation chromosome. In the process of synapsis, the length adjustment phenomenon in the trivalent occurred: a. There is nonhomologous synapsis between the two short arms of the acrocentrics (13;17). The length of short SC varied. b. The position of the short SC, which is on the long SC(homologous synapsis of rob(13; 17) and 13, 17) moved, from one-fourth of long SC to one-tenth of it, near the end of 17 arm. These phenomenon is the result of a gradual length adjustment of lateral elements of 13,17 to the lateral element of the rob (13;17). We has discussed the mechanism of the trivalent synaptic adjustment, and it's important use to control the chiasmata and disjunction of the chromosomes.

Animals↗
PubMed1994

[Effects of arsenic on the offspring development in mice].

Effects of arsenic exposure on offspring development were studied in pregnant mice. The results showed arsenic contents of the body and brain tissue increased and the structure of neural cells in cerebral cortex became abnormal after exposure. The offspring neurobehavioral development appeared retardant and the proportion of their peripheral lymphocytes with alpha-naphthalene acetate enzyme (ANAE) declined in a mice group with exposure to 0.75 mg/kg arsenic, and the offspring body weight gain slowed after weaning, blood cholinesterase activity and serum level of haemolysin declined significantly in a group with 4.50 mg/kg. It indicated arsenic could affect embryonic and offspring development in mice through pregnant exposure.

Animals↗
PubMed1994

Age-related human mtDNA deletions: a heterogeneous set of deletions arising at a single pair of directly repeated sequences.

Deletions in mtDNA accumulate during the human aging process, arising from either intramolecular illegitimate recombination or strand slippage during replication, which results in subgenomic mtDNA molecules. We identify here two classes of mtDNA deletions--class A deletions, which are homogeneous at the breakpoints, with all subgenomic molecules therefore being identical in size, and class B deletions, which arise from a less stringent process that gives rise to heterogeneity at the breakpoints, with the subgenomic molecules being of slightly different sizes. A novel approach is described that offers a global overview of the populations of different deletions in individual tissues. It is based on PCR cycle-sequencing reactions that are carried out directly on mtDNA segments, amplified by PCR from total cellular DNA. The results show a clear size homogeneity of the subgenomic mtDNA molecules representative of class A, which carry a commonly detected 4,977-bp deletion occurring at a pair of 13-bp directly repeated sequences. In this case, precisely one copy of the repeat is retained in the subgenomic molecules. We then describe a class B situation comprising a family of at least nine closely related 8.04-kb deletions involving the same pair of 5-bp direct repeats. In this situation, the breakpoints differ at the base-pair level (8,037-8,048-bp deletions); the subgenomic molecules retain > 1 copy, 1 copy, or < 1 copy of the 5-bp repeat. In different tissues from either the same individual or among different individuals, there is a widely variable occurrence of particular deletions in the subgenomic mtDNA population within this class B set. Class B deletions offer a new approach for studying the accumulation of mtDNA deletions, thereby providing insight into the independent somatic origin of mutated mtDNA molecules, both in aging and in mitochondrial diseases. We also report a convenient method for ascertaining whether a given PCR product results from the amplification of a subgenomic mtDNA template, on the basis of the selective degradation of full-length mtDNA molecules prior to PCR.

Adult↗
PubMed1994

Apoptosis leads to photoreceptor degeneration in inherited retinal dystrophy of RCS rats.

PURPOSE: To determine the pathogenetic mechanism of photoreceptor cell degeneration in the inherited retinal dystrophy in Royal College of Surgeons (RCS) rats. METHODS: The dystrophic retinas of the pink-eyed RCS (RCS-rdy-p) rats were examined for DNA fragmentation by agarose gel electrophoresis of retinal DNA and by TdT-mediated biotin-dUDP nick-end labeling (TUNEL) in paraffin sections. Rats ranging in age from 3 to 60 days were examined. RESULTS: Agarose gel electrophoresis of retinal DNA isolated from animals 25, 30, 35, and 40 days old showed a ladder pattern of degradation with bands corresponding to multiples of 180 to 200 base pair subunits. TUNEL study showed increasing labeling of photoreceptor cells with progression of the retinal dystrophy of the RCS rats. CONCLUSIONS: Apoptosis is the dominant mechanism of photoreceptor degeneration in the RCS rat, which has a genetic defect in the phagocytic activity of retinal pigment epithelium. The onset of the degeneration appeared to vary between rod cells in the different regions of the eye.

Animals↗
PubMed1993

Transactivation of the early SV40 promoter by avian infectious laryngotracheitis virus in avian hepatoma cells.

An avian hepatoma cell line has been reported to be suitable for the cultivation of avian laryngotracheitis virus (ILTV) (Scholz et al. (1993) J. Virol. Methods, 273-286; Guo et al. (1993) Am. J. Vet. Res., in press). To provide information for the establishment of avian expression systems and for the construction of avian recombinant viruses, five expression plasmids were constructed to test two avian viral and two mammalian viral promotors for their suitability and strength for gene expression in this cell line. Chicken hepatoma cells were transfected with plasmids carrying the bacterial beta-galactosidase (beta-gal) gene as a reporter gene. The beta-gal gene of three plasmid constructs expressed in both E. coli and avian hepatoma cells, while the beta-gal gene of two other constructs expressed only in avian hepatoma cells. The beta-gal gene expressed independently of any viral infection when under the control of the early Rous sarcoma virus (RSV) promoter or the immediate-early cytomegalovirus (CMV) promoter. However, expression of beta-gal gene under the control of the SV40 early promoter/enhancer and the ILTV TK promoter was greatly potentiated when the transfected cells were co-infected with ILTV. This finding provides a system for the enhancement of gene expression in avian cells, especially when ILTV is used as vector.

Animals↗
PubMed1993

Coordination of vanadyl(IV) cation in complexes of S-adenosylmethionine synthetase: multifrequency electron spin echo envelope modulation study.

S-Adenosylmethionine (AdoMet) synthetase requires two freely dissociable divalent cations for activity, and its activity is greatly stimulated by certain monovalent cations (K+, Tl+). Omission of the native Mg2+ cations prevents enzyme-catalyzed reactions, although the substrates and products still bind. Vanadyl (oxovanadium, VO2+) serves as a convenient paramagnetic probe of the substrate-independent, divalent cation binding site in the enzyme. In the present study, multifrequency electron spin echo envelope modulation (ESEEM) is employed to explore the cation's coordination sphere in several functionally relevant complexes. In the substrate complex enzyme.VO2+.ATP.methionine.K+, an equatorially coordinating 14N ligand is found, with Aiso = 4.3 MHz. Selective 15N labeling of the epsilon-amino nitrogens of all lysine residues in the protein reveals that lysine is the source of the ligand. A lysine 14N ligand is also observed in the intermediate complex enzyme.VO2+.AdoMet.PPPi.K+, with Aiso = 4.8 MHz, and in the initial product complex enzyme.VO2+.AdoMet.PPi.K+. In the subsequent product, enzyme.VO2+.AdoMet.K+ (formed upon dissociation of PPi), the methionyl amino nitrogen of AdoMet coordinates VO2+ (Aiso = 5.3 MHz), and the lysine ligand is lost. In each complex, the monovalent cation activator can be changed from K+ to Tl+ or Na+ with no effect on the ESEEM spectra. Combination of the ESEEM data from this study with previous CW data [Markham, G. D. (1984) Biochemistry 23, 470-478] leads to identification of three of the equatorial ligands to VO2+ and places constraints upon the identity of the fourth ligand, in both the substrate and product complexes. A hypothetical outline of changes in the metal coordination scheme during the reaction is presented, based upon these results.

Adenosine Triphosphate↗
PubMed1993

The receptors activated by exogenous and endogenous opioids in the superior cervical ganglion of the cat.

Nicotinic transmission in the superior cervical ganglion of the cat was studied in vivo and in vitro by recording the postganglionic compound action potential evoked, under partial block with hexamethonium, by supramaximal 0.2 Hz stimulation of the cervical sympathetic trunk. The compound action potential was depressed following a stimulus train (5 Hz, 40 s) applied to the same set of axons. The inhibition was antagonized by naloxone, suggesting mediation by endogenous opioids. Agonists selective for mu-, delta- and kappa-opioid receptors, injected into the arterial supply of the in situ ganglion or added to the perfusion fluid in the in vitro ganglion, also produced a naloxone-sensitive inhibition of the compound action potential. The synaptic inhibition was antagonized by the delta-selective antagonist ICI 174,864 and by the mu-selective antagonist CTAP, but not by the kappa-selective antagonist Nor-BNI. These results suggest that all three main types of opioid receptors are present in the ganglion but only mu- and delta-receptors are involved in the inhibition of ganglionic transmission mediated by the endogenous opioids.

Amino Acid Sequence↗
PubMed1993

Occurrence of a particular base substitution (3243 A to G) in mitochondrial DNA of tissues of ageing humans.

Allele-specific polymerase chain reaction has been used to demonstrate the occurrence, during the human ageing process, of the mutation A to G at nucleotide position 3243 on mitochondrial DNA. An oligonucleotide with a 3'-end specific to this mutation was designed to selectively amplify DNA bearing this mutation under annealing temperature conditions that efficiently discriminate between normal and mutant mitochondrial DNA templates. Seven out of 38 adult tissues tested were found to contain this mutation, whereas the mutation could not be detected in any of the 16 infant tissues analyzed. The present demonstration of an age-related point mutation adds to the growing list of mutations in human mitochondrial DNA, till now almost exclusively large deletions, that accumulate in human tissues as a function of age. The method described here has general application in the detection of other age-related point mutations in human mitochondrial DNA.

Adenine↗
PubMed1993

Mapping of ben genes of Pseudomonas aeruginosa.

Four ben genes responsible for the conversion of benzoate to catechol in Pseudomonas aeruginosa PAO have been mapped to a 4.6 kb KpnI fragment, ben-1 and ben-4 were known to be separate genes but now ben-1508 has been found to be different from ben-2. The two genes were distinguished by Tn5 mutagenesis of a cosmid clone and deletion mapping. It is likely that the four genes mapped (ben-4, ben-2, ben-1508 and ben-1) correspond to the previously characterized benR (regulatory gene) and benABC (benzoate dioxygenase) respectively.

Benzoates↗
PubMed1993

Use-dependent fade and two-rate recovery of a naloxone-sensitive inhibition in the cat superior cervical ganglion.

In anaesthetized cats, a short train to the cervical sympathetic trunk (CST), of frequency between 0.5 and 5.0 Hz, inhibited the postganglionic compound action potential (CAP) evoked by a test shock to the CST. When the CST was split into two bundles, the inhibition was obtained both homosynaptically and heterosynaptically. The inhibition was antagonized by naloxone and enhanced by peptidase inhibitors. Leu-enkephalin (ENK), injected into the arterial supply of the superior cervical ganglion (SCG) depressed the CAP. The ENK-evoked inhibition was antagonized by naloxone, enhanced by peptidase inhibitors and was occluded by the train-evoked inhibition. After prolonged stimulation of the CST (5-20 min at 5 Hz), the inhibition produced by a short train was depressed (faded). The fade was greater the longer the stimulation. After 20 min of stimulation the inhibition was absent. At this time the depressant effect of ENK was unchanged. When only one bundle of the split CST was stimulated at 5 Hz for 20 min, only the inhibition produced by that bundle faded, although both bundles converged onto a common set of ganglion cells. Thus, the fade is not due to receptor desensitization but more likely to failure to release the inhibitory mediator by the overstimulated axons. When, after 20 min of 5 Hz stimulation, no further stimuli were applied, the inhibition recovered in 60 min (fast recovery). However, recovery was slower when stimulation lasted longer than 20 min. Recovery took three days when stimulation lasted 80 min (slow recovery). The inhibition was markedly depressed after application of colchicine to the CST three days earlier.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1993

Mapping of the ben, ant and cat genes of Pseudomonas aeruginosa and evolutionary relationship of the ben region of P. aeruginosa and P. putida.

Genes responsible for the utilization of benzoate, anthranilate or catechol (ben, ant, cat) of Pseudomonas aeruginosa PAO were mapped precisely using a cosmid clone carrying all these genes. Genes were localized either by subcloning and complementation or by Tn5 mutagenesis and mapping of the Tn5 insertions. To achieve this, a novel Tn5 mutagenesis procedure was developed by constructing a Tn5 insertion derivative of the Escherichia coli strain S17-1. Preliminary mapping of the ben cat genes of P. putida PPN was accomplished by complementation using a PPN cosmid bank. Sequence homology was demonstrated by Southern hybridization between the ben regions of both P. aeruginosa and P. putida, implying an evolutionary relationship of this chromosomal region of these two pseudomonads.

Chromosome Mapping↗
PubMed1993

Bradyrhizobium japonicum rhizobitoxine genes and putative enzyme functions: expression requires a translational frameshift.

Some strains of Bradyrhizobium japonicum produce rhizobitoxine, a phytotoxin that causes foliar chlorosis on susceptible host plants. We have previously obtained Tn5-induced rhizobitoxine null mutants of B. japonicum. DNA sequence analysis of the region surrounding two Tn5 insertions identifies two overlapping open reading frames. The first open reading frame (rtxA) predicts a 54-kDa protein for which the N-terminal 280 residues have sequence similarity to serine: pyruvate aminotransferase. The sequence homology to aminotransferase is consistent with the involvement of this gene in serinol production, a likely intermediate in rhizobitoxine biosynthesis. Previously, a mutant in this open reading frame was shown not to make serinol. The predicted amino acid sequence of the second open reading frame (rtxB) has similarity to yeast O-acetylhomoserine sulfhydrolase. This enzyme function is similar to that required for dihydrorhizobitoxine synthase. The DNA sequence shows that the rtxB open reading frame overlaps rtxA, suggesting that expression of rtxB requires a -1 translational frameshift. Protein expression experiments demonstrate production of an RtxAB fusion protein. The ability of the overlapping rtxA and rtxB sequences to promote a translational frameshift was confirmed in a heterologous expression system. In Escherichia coli, this frameshift appears to be unusually efficient, occurring at a frequency of 80-90%.

Amino Acid Sequence↗
PubMed1993

Cadmium-induced arteriolar constriction in skeletal muscle microcirculation.

Cadmium, an environmental pollutant, is known to induce hypertension in animal models, in part via an increase in peripheral vascular resistance. Since prior studies have investigated the vascular effects of cadmium using large, nonresistance arteries, we directly assessed cadmium's action on resistance size arterioles in skeletal muscle using the intact rat cremaster muscle preparation. Cadmium evoked a concentration-dependent constriction of the large arterioles (120 to 50 microns in diameter) but elicited no change in the diameter of smaller arterioles (30 to 15 microns). Blockade of alpha-adrenergic receptors did not diminish the constrictor response of the larger arterioles to cadmium, but bathing the cremaster muscles with a solution containing low calcium attenuated the arteriolar constriction to cadmium. Calcium repletion caused the arterioles to constrict further. These observations provide the first direct evidence that cadmium constricts resistance arterioles in skeletal muscle. The cadmium constriction: (1) is selective for the large arterioles, (2) is not mediated by alpha-adrenergic receptors, and (3) is influenced by the extracellular level of calcium. We conclude that arteriolar constriction in skeletal muscle tissue may play a role in the hypertensive actions of cadmium.

Animals↗