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Biomedical subjects

J Earl

Publications and source records attributed to J Earl.

28 records · Page 2Linked to original sources
PubMed1990

A urinary cysteine-halothane metabolite: validation and measurement in children.

An attempt was made in children to identify a urinary halothane-cysteine conjugate which had been described previously in adult patients following administration of halothane. If this conjugate was found it would indicate that a reductive metabolite of halothane binds covalently with the sulphydryl-containing amino acid, cysteine, a reaction which could lead to hepatic injury. The potential halothane-cysteine conjugate, N-acetyl-S-(2-bromo-2-chloro-1,1-difluoroethyl)-L-cysteine (acetyl BCFEC), was prepared and the identity of the compound established using hydrogen-1 and carbon-13 NMR spectroscopy and methane chemical ionization mass spectrometry. A measurement technique for acetyl BCFEC was developed using HPLC with u.v. detection at 200 nm. In six children after halothane anaesthesia, one child being studied twice, urine was collected for up to 1 week and analysed for acetyl BCFEC. Little or no acetyl BCFEC was detected in any of the 43 urine samples tested, indicating that in children it is not a significant urinary metabolite of halothane.

Acetylcysteine↗
PubMed1990

Halothane metabolism in children.

Halothane (1% v/v inspired) was administered for 60 min to six children of mean age 74 months (range 14-119 months). Uptake of halothane was measured from the difference in the concentration in inspired and expired gas and varied from 176 to 310 mg kg-1, depending on minute ventilation. After administration of halothane ceased, its elimination in expired gas was measured in four patients until the conclusion of anaesthesia; 32-37% of the absorbed halothane was expired 90 min after halothane administration ceased. Urinary excretion of trifluoroacetic acid, fluoride and bromide was measured for up to 1 week. Of the absorbed halothane, 11.4% (range 6.3-18.2%) was excreted in urine as trifluoroacetic acid and 0.37% (range 0.10-0.64%) as inorganic fluoride. The urinary half-life of trifluoracetic acid was 41.8 h (range 10.4-59.1 h). The quantitative and qualitative metabolism of halothane via the reductive and oxidative pathways in children are comparable to values found in adults. No differences in the metabolism of halothane by children were found which would explain the different incidence of halothane-associated hepatitis compared with adults.

Anesthesia, Inhalation↗
PubMed1989

A field study report of intensive computer keyboard training with schoolchildren.

A video-based keyboard skills training programme was used to teach primary and secondary school students to touch type, in ten 45-min lessons. Previous research (Glencross and Bluhm, 1986) had found the programme to be successful in training a variety of personnel in the workforce. In all, 197 students (105 females, 92 males) received instruction over a two-week period. The influence of age (11-12, 13-14, 15-16, 17-18 years) and sex on keyboard operating speed and accuracy were examined. Speed tests were conducted after the second and ninth lesson. Significant improvements in speed of typing were recorded for all age categories. Age and sex were found to be associated with speed of typing and rate of improvement across tests. Error rates remained constant across tests.

Journal Article↗
PubMed1975

Some characteristics of pre- and post-synaptic inhibitory receptors at the hermit crab neuromuscular junction.

1 The effects of gamma-aminobutyric acid (GABA), beta-guanidinopropionic acid (betaGP) and picrotoxin on the pre- and post-synaptic receptors of the hermit crab neuromuscular junction were studied quantitatively usine electrophysiological techniques. Reductions in excitatory junction potential (e.j.p.) amplitude and membrane resistance were measured simultaneously from the same cells. 2 The pre- and post-synaptic receptors were activated by the same order of concentration of GABA, whereas betaGP stimulated the pre-synaptic receptors at a concentration ten times lower than was required to affect the post-synaptic membrane. 3 Picrotoxin appeared to antagonize the pre-synaptic action of betaGP in a competitive manner. The affinity constants (+/- s.e. mean) for picrotoxin 5 times 10(-6)M and 2 times 10(-4)M were 6.80(+/-0.46) times 10(5)M-1 and 6.42(+/-1.8) times 10(5)M-1 respectively. 4 The effect of GABA on e.j.p. amplitude also appeared to be antagonized competitively by picrotoxin whereas the post-synaptic effect was antagonized in a non-competitive manner. 5 Possible differences in the nature of the pre- and post-synaptic receptors are discussed.

Animals↗
PubMed1974

Electrophysiological investigation of GABA-mediated inhibition at the hermit crab neuromuscular junction.

1. The inhibitory neuromuscular junction of the abductor muscle of the large claw of the hermit crab (Eupagurus bernhardus) was investigated using electrophysiological intracellular techniques in order to elucidate further the relative contributions of the pre- and post-synaptic mechanisms of action of GABA and of neural inhibition.2. The electrical constants of the post-synaptic membrane, calculated using the equations for a ;short cable' model, were characteristic of a poorly developed electrical excitability; the specific membrane resistance was usually < 1000 Omega cm(2) and the specific membrane capacitance was > 40 muF/cm(2).3. Stimulation of the excitatory axon to the abductor muscle of the large claw at a frequency of 20 Hz evoked highly facilitating excitatory junction potentials (e.j.p.s); stimulation of the inhibitory axon (60-220 Hz) during the excitatory train elicited inhibition which was manifest as an attenuation of the e.j.p.s.4. The addition of gamma-aminobutyric acid (GABA) to the bathing solution produced a dose-dependent reduction of e.j.p. amplitude and membrane resistance. The inhibitory effect of concentrations (5 x 10(-5) and 1 x 10(-4)M) which caused a 40-75% e.j.p. attenuation could largely be accounted for by a post-synaptic action on membrane conductance.5. Experiments with picrotoxin suggest that presynaptic inhibitory mechanisms have an important role in neurally evoked inhibition.6. Picrotoxin (1-5 x 10(-5)M) effectively blocked neural inhibition and the actions of GABA in this preparation, whereas bicuculline proved to be considerably less potent and therefore less useful as a physiological tool for studying GABA-mediated inhibition in crustacea.

Action Potentials↗