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Biomedical subjects

H H Liu

Publications and source records attributed to H H Liu.

80 records · Page 5Linked to original sources
PubMed1985

Penicillin tolerance in multiply drug-resistant natural isolates of Streptococcus pneumoniae.

Five of six multiply drug-resistant clinical isolates of Streptococcus pneumoniae from South Africa demonstrated penicillin tolerance. In contrast to the common wild-type strains of pneumococci, treatment of the tolerant strains with penicillin above the minimum inhibitory concentration did not induce cell wall degradation, lysis, or leakage of intracellular components, and the rate of loss of viability was reduced compared with that of nontolerant strains. While these South African strains contained lower specific activity of autolytic enzyme than did nontolerant strains, the residual autolytic activity (15%-26% of the nontolerant wild type) was much more than that found in lysis-defective laboratory mutants of pneumococci (less than or equal to 1%); the rate of penicillin-induced lysis did not correlate with the specific activity of residual autolysin. Also, in contrast to the complete lysis resistance of lysis-defective mutants to all lytic agents, the tolerant South African strains were resistant primarily to lysis by beta-lactam antibiotics but could still be lysed by other cell wall inhibitors (e.g., cycloserine) and detergents. The penicillin resistance and penicillin tolerance traits could be separated by genetic transformation. We suggest that the drug-specific tolerance of the South African pneumococcal strains is related to some alteration in the control of autolysin activity.

Humans↗
PubMed1983

A computer system for real-time data acquisition and analysis of biopotentials and quantal content at the neuromuscular junction.

A computerized data acquisition system for on-line analysis of the parameters of neuromuscular transmission is described. Both hardware usage and software methodologies are discussed with regard to sampling in real-time and analyzing miniature end-plate potentials (MEPPs), end-plate potentials (EPPs) and quantal content of the evoked transmitter release. Significant features of the program include: (1) automatic threshold determination for MEPP detection; (2) the use of a circular buffer to give pre-trigger information; (3) real-time noise spike rejection; (4) an automatic procedure for EPP failure detection; (5) rapid quantal content determinations by several methods as well as complete MEPP and EPP waveform analysis. The system has proven both accurate and reliable during more than two years of use. Advantages of the system over conventional methods include: (1) increased accuracy and efficiency in data analysis; (2) immediate availability of results; (3) conventional data storage; (4) flexibility to meet changing requirements.

Action Potentials↗
PubMed1983

Reduction of miniature end-plate potential amplitude in extraocular and limb muscles in an animal model of myasthenia gravis.

Miniature end-plate potential (MEPP) amplitudes of the superior oblique extraocular muscle (EOM) and forelimb flexor digitorum longus muscle (FDL) of rats with experimental autoimmune myasthenia gravis (EAMG) were expressed as reductions from mean MEPP amplitudes of the respective muscles of pair-matched control animals. Postjunctional blockade of neuromuscular transmission at EOM end-plates was no greater than at limb muscle end-plates. In contrast, the amount of reduction measured in EAMG-affected FDLs (52.3%) was marginally, but significantly, greater than that in EOMs (38.3%). A weak correlation was present between the MEPP reduction observed in an animal's FDL and that recorded in its EOM.

Acetylcholine↗
PubMedDate not supplied

Presynaptic and postsynaptic actions of procainamide on neuromuscular transmission.

Procainamide (PA), a cardiac anti-arrhythmic agent, was applied in vitro to the rat neuromuscular junction and its effect on neuromuscular transmission was investigated using intracellular microelectrode recording techniques. Clinically relevant doses of PA produced a dose-dependent decrease in the amplitude of spontaneous miniature end-plate potentials (MEPPs) and a marked increase in the half-decay time without altering MEPP frequency or resting membrane potential. The amplitude of impulse-evoked end-plate potentials was also reduced in a similar dose-dependent manner, with a marked prolongation of the decaying phase. Direct quantal analysis using magnesium-blocked preparations showed that the drug also caused a reduction in the mean number of acetylcholine quanta released per nerve impulse. This presynaptic inhibitory effect of the drug, however, contributed less to the overall blocking action than did the postsynaptic effect. The junctional effects of the drug were completely reversible, with all affected parameters returning to the control levels after washout of PA with control solution. These direct inhibitory actions on neuromuscular transmission could account for the clinical exacerbations associated with the administration of PA to patients with myasthenia gravis and other neuromuscular diseases.

Animals↗
PubMedDate not supplied

Lamellar refractive surgery with scanned intrastromal picosecond and femtosecond laser pulses in animal eyes.

PURPOSE: To evaluate the use of scanned intrastromal picosecond and femtosecond laser pulses in lamellar refractive surgical procedures. METHODS: Intrastromal corneal photodisruption was performed in fresh porcine and primate cadaver eyes with a solid-state femtosecond laser. Laser pulses were focused 150 to 200 microns below the epithelial surface and scanned in a spiral pattern to create a plane. A flap was made by scanning an arc pattern from the plane of the spiral to the surface of the cornea. Tissue plane separation was graded using a standard scale, while internal surfaces were analyzed by scanning electron microscopy. Comparison was made to a picosecond laser system using the same delivery system device. Creation of a stromal lenticule for in situ keratomileusis was also demonstrated and compared with both laser systems. RESULTS: For femtosecond pulses, tissue separation was achieved best with pulse energies from 4 to 8 microJ and spot separations from 10-15 microns. Picosecond pulses accomplished less complete separations with pulse energies of 25 microJ and spot separations from 10 to 20 microns. Surface quality corresponded to dissection results, with high-grade dissections resulting in a smooth surface appearance, versus a more irregular surface for low-grade dissections. Although high-grade dissections could be created with picosecond pulses (with optimal parameters) in ex vivo porcine eyes, only femtosecond parameters produced similar results in ex vivo primate eyes. CONCLUSION: In contrast to previous attempts using picosecond lasers which require additional mechanical dissection, high precision lamellar refractive surgery may be practical with femtosecond laser pulses.

Animals↗