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Biomedical subjects

L S Chen

Publications and source records attributed to L S Chen.

At least 91 records · Page 5Linked to original sources
PubMed1989

[Infections in the early postoperative period following keratoplasty--a report of seven cases].

Keratoplasty was performed on 3482 eyes from 1965 to 1986 in our hospital. Five eyes (0.14%) were infected in the early postoperative period. Two eyes had endophthalmitis. These seven eyes were operated on again and with local and systemic antibiotics treated as well. Followed up for 36 days to 7 years, six eyes remained safe (5 eyes transparent and 1 eye semi-transparent.) The visual acuity reached 0.3 in two eyes, 0.2 in one eye and finger counting to 0.1 in three eyes. The seventh eye was enucleated because of serious infection. Several factors of infection in the early postoperative period following keratoplasty, causative organisms, the relations between the types of operation in the early postoperative period following keratoplasty were also discussed.

Adolescent↗
PubMed1989

Effect of rhodamine 123 and total glycosides from tripterygium wilfordii (GTW) on ultrastructures, survival and fertilizing capacity of human sperm in vitro.

Human sperms were treated with rhodamine 123 or GTW in vitro. Comparisons were made of survival, fertilizing capacity and ultrastructures of sperms which had been exposed to different concentrations and treatment durations of the agents. The results showed that no prominent change could be observed when treated with lower doses. However, at higher concentrations of rhodamine 123, mitochondria were found to be swollen, vacuolated and deranged instead of surrounding the flagellar axoneme in the normal spiral way, and the mitochondrial cristae were broken or had disappeared. In some sperms, cracks at the flagellar axoneme and concave defects in the acrosome were seen. The sperms lost their fertilizing capacity, though some of them were still alive, whereas the sperms treated with GTW showed no morphological damage and maintained their ability to penetrate the hamster egg. Our results suggest that rhodamine 123 is a prospect in the search for an anti-sperm contraceptive.

Animals↗
PubMed1987

Microinjection of a benzodiazepine into substantia nigra elevates kindled seizure threshold.

The purpose of these experiments was to initiate investigations of the brain site(s) at which the benzodiazepines exert their anticonvulsant effect. We examined the effects of microinjections of clonazepam into substantia nigra (SN) on seizure threshold in the kindling model. We also examined the distribution of microinjected [3H]methylclonazepam with autoradiographic methods. Microinjection of clonazepam bilaterally into substantia nigra pars reticulata (SNR), but not nearby, produced a 75% elevation of generalized seizure threshold. Quantitative analysis of autoradiographic studies indicated that the vast majority of [3H]methylclonazepam was distributed within 400 micron of the injection cannula tip; even optimally placed injections did not result in drug access throughout the entire SN. The data demonstrate that local application of an anticonvulsant benzodiazepine to the substantia nigra alone is sufficient to suppress seizures. We suggest that the substantia nigra is one site at which systemically administered benzodiazepines act to suppress seizures.

Animals↗
PubMed1987

A set of positively regulated flagellar gene promoters in Caulobacter crescentus with sequence homology to the nif gene promoters of Klebsiella pneumoniae.

The study reported here describes nuclease S1 mapping of the in-vivo transcription start sites of transcription units I and III of the hook gene cluster of Caulobacter crescentus. We show that transcription units I and II of this flagellar (fla) gene cluster, which have divergent promoters with transcription start sites separated by 218 nucleotides, are under positive transcriptional control by genes in transcription unit III. The promoters of transcription units I, II, and III were compared with flagellin gene promoters P25, P27 and P29 recently identified in C. crescentus. Promoters PII, P25, and P27, which are under positive regulation by transcription units III to V have strongly conserved sequence elements at -13 and -24 with the consensus sequence (C/T)TGGC(C/G)C-N5-TTGC. The -13, -24 sequence elements are not well conserved in promoter PI, but the promoter does contain a copy of the -13 and -24 consensus sequence 23 base-pairs upstream (PI). The C. crescentus fla gene promoters are not homologous to the canonical Escherichia coli -10, -35 promoter sequence, but they are very similar to the -12, -24 nif gene promoter sequence reported for Klebsiella pneumoniae and Rhizobium sp. The four positively regulated fla gene promoters examined here also share a third conserved element designated II-1, with the consensus sequence C-C-CGGC--AAA--GC-G, located at approximately -100. We speculate that the conserved sequence elements mapping at -13, -24 and -100 are cis-acting regulatory elements required for the transcription and periodic regulation of these fla genes in the C. crescentus cell cycle.

Base Sequence↗
PubMed1986

Identification, nucleotide sequence, and control of developmentally regulated promoters in the hook operon region of Caulobacter crescentus.

The major flagellar proteins, including the flagellins and the hook protein, are synthesized periodically in the Caulobacter crescentus cell cycle at the time of flagellum assembly. Although fla genes are regulated at the transcriptional level [Ohta, N., Chen, L.-S., Swanson, E. & Newton, A. (1985) J. Mol. Biol. 186, 107-115], the 5' regulatory regions of C. crescentus genes have not been identified. We describe here the results of nuclease S1 protection assays that map the 5' ends of mRNAs synthesized in vivo from transcription units II (hook operon) and II.1 of the hook gene cluster and locate the corresponding promoter regions PII and PII.1. The two promoters are regulated with different periodicities in the cell cycle and have different genetic requirements for expression. The failure to detect transcripts from either PI or PII in Escherichia coli suggests that developmentally regulated promoters of C. crescentus have different recognition sequences from those of E. coli. There is little nucleotide sequence homology between PII and PII.1. There are, however, three regions of homology between PII and the nucleotide sequence 5' to the 29-kDa-flagellin-related gene, and two of these are in regions of dyad symmetry. We discuss the possibility that DNA-protein interactions at homologous nucleotide sequences like those identified in PII are part of a regulatory gene cascade that participates in timing fla gene expression in the C. crescentus cell cycle.

Bacterial Proteins↗
PubMed1985

Transcriptional regulation of a periodically controlled flagellar gene operon in Caulobacter crescentus.

Temporal regulation of flagellar gene expression in Caulobacter crescentus has been examined by a detailed analysis of the flbG-flaJ-flbH-flaK hook operon. The approximate location of the promoter for this 4.4 X 10(3) base-pair transcriptional unit was determined by deletion mapping, and the flaK gene was shown by nucleotide sequencing to code for the hook protein. flaK messenger RNA was quantified by S1 nuclease mapping with an internal restriction fragment of the gene as the 5'-labeled DNA probe. The results of these assays provide the first direct evidence that periodic expression of a flagellar gene in the C. crescentus cell cycle is regulated at the transcriptional level. The effect of altering the time of gene duplication in the cell cycle was examined by subcloning the complete hook operon on a plasmid that replicates throughout the S phase. The normal periodicity of flaK transcription and translation was maintained in this merodiploid strain, which suggests that replication alone is not sufficient to initiate flagellar gene expression. We also show that the three adjacent transcriptional units III, IV and V are required in trans for transcription of the book operon, and we discuss the possible role of these genes in the hierarchical regulation of the flagellar gene expression.

Bacterial Proteins↗
PubMed1984

Barium-induced electro-mechanical uncoupling in myocardial cells.

The heart of the adult moth Hyalophora cecropia requires extracellular calcium to maintain electrogenesis as well as tension development. In this study we ask whether the processes of autorhythmicity, driven electrogenesis and tension development require calcium specifically or whether the divalent cation Ba2+ can be substituted for calcium to support these activities. Ba2+ substituted for Ca2+ in equimolar amounts caused a marked (25 mV) hyperpolarization, suppression both of pacemaker activity and of tension development in spontaneously beating semi-isolated heart cells. Heart cells bathed in Ba2+ saline and paced by action potentials (produced by external stimuli) of greatly increased amplitude, prolonged phase 2 (plateau) and increased latency, and after 30 min, no mechanical activity was observed. These changes were completely reversible when calcium was reintroduced. We conclude that Ba2+ substitution for Ca2+ is an effective electromechanical uncoupler in moth heart cells. Although Ba2+ can support electrogenesis, it cannot replace 'trigger'-Ca2+ needed to release calcium from sarcoplasmic stores to effect tension development.

Action Potentials↗
PubMed1984

Plasma concentrations of 6-keto-prostaglandin F1 alpha, thromboxane B2 and platelet aggregation in patients with essential hypertension.

Plasma concentrations of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 (TXB2), the stable nonenzymatic metabolites of prostacyclin and TXA2, respectively, were assayed in 26 patients with essential hypertension and 25 normotensive subjects to investigate the pathophysiological role of prostacyclin and thromboxane A2 (TXA2) in essential hypertension. A tourniquet test was also performed on the upper limb of each subject to study the reactivity in peripheral vessels. In addition, platelet aggregation was investigated. There were significantly increased plasma TXB2 concentrations and platelet aggregation and significantly decreased plasma 6-keto-PGF1 alpha concentrations in patients with essential hypertension as compared with normotensive subjects. The responses to tourniquet tests were also different. There were significantly increased plasma concentrations of 6-keto-PGF1 alpha and TXB2 and platelet aggregation in normotensive subjects, but no significant changes with essential hypertension as compared to resting values. These results indicate that the reduction of plasma prostacyclin and increase of plasma TXA2 may contribute to the maintenance of blood pressure elevation in patients with essential hypertension. In addition, it is also suggested that increased prostacyclin generation in normotensive subjects during the tourniquet test is a protective mechanism. In patients with essential hypertension, the protective activity is reduced.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

Peripheral projections of fascicles in the human median nerve.

Intraneural microstimulation combined with microneurography was employed to study the degree of mixing of muscle and skin nerve fibres at two levels in the human median nerve, and to delineate the area of skin supplied by a fascicle. It was found that about half the fascicles at upper arm level appeared to supply exclusively skin or muscle, while the remainder were considerably committed to one or the other. Further, the projection territories of skin nerve fascicles, both at the wrist and in the arm, tended to be discrete, confluent areas covering no more than 20 per cent of the median nerve territory. At the wrist fascicular territories usually resembled the innervation area of a single palmar digital nerve while in the upper arm they tended to cover a digital interspace. These findings suggest that most of the rearrangements of spinal root fibres into terminal nerve branch groupings occur at brachial plexus level, while the intraneural fascicular plexus may act as a safety mechanism allowing for nondermatomal overlap at proximal level.

Adult↗