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R L Parsons

Publications and source records attributed to R L Parsons.

At least 109 records · Page 6Linked to original sources
PubMed1978

Desensitization onset and recovery at the potassium-depolarized frog neuromuscular junction are voltage sensitive.

The influence of voltage on the time-course of desensitization onset and recovery has been studied at the frog neuromuscular junction. The activation-desensitization sequence was determined from carbachol-induced end-plate currents in potassium-depolarized fibers voltage-clamped either to -40 mV or +40 mV. The time-course of both desensitization onset and recovery developed exponentially, with onset occurring more rapidly than recovery. Desensitization onset was voltage dependent, the onset time constant being 8.3 +/- 1.3 s (11 fibers) at -40 mV and 19.3 +/- 3.4 s (15 fibers) at +40 mV. Recovery from desensitization was also influenced by voltage. The extent of recovery after 2 min was 80.4 +/- 6.3% in those fibers voltage-clamped to -40 mV and 57.4 +/- 3.6% in those fibers voltage-clamped to +40 mV. The voltage dependence of desenistization onset and recovery did not result from a difference in ability to control voltage at these two levels of membrane potential. These results demonstrate that in the potassium-depolarized preparation the processes controlling both desensitization onset and recovery of sensitivity from the desensitivity from the desensitized state are influenced by membrane voltage.

Animals↗
PubMed1978

Plasma, bone, hip capsule and drain fluid concentrations of ampicillin and flucloxacillin during total hip replacement after intravenous bolus injection of magnapen.

1. A rapid intravenous bolus injection of 4.0 g Magnapen (which contains 2.0 g of ampicillin and 2.0 g of flucloxacillin) was to seven patients undergoing total hip replacement immediatly before induction of general anesthesia. Postoperatively the patients patients received 2.0 g Magnapen by intramuscular injection every 6 h for up to 72 h until removal of the wound drains. 2. The plasma, bone, hip capsule and drain fluid concentrations of ampicillin and flucloxacillin were measured by a differential small plate microbiological assay method using Sarcina lutea and a penicillinase producing Staph. aureus Russell as the test organisms. 3. The mean +/- s.e. mean concentrations of ampicillin after this regimen were 4222.2 +/- 285.0 microgram/ml (plasma), 65.6 +/- 1.3 microgram (g (hip capsule), 19.1 +/- 3.8 microgram/g (cancellous bone), and 211.1 +/- 65.6 microgram/g (ground up bone) respectively. 4. The mean +/- s.e. mean flucloxacillin concentrations after this regime were 137.2 +/- 28.4 microgram/ml (plasma), 61.8 +/- 15.0 microgram/g (hip capsule), 47.1 +/- 9.5 microgram/g (cancellous bone) and 139.4 +/- 21.8 microgram/g (ground up bone) respectively. 5. An intravenous bolus injection of Magnepen (4.0 g), given immediately before induction of general anaesthesia, provides concentrations of ampicillin and flucloxacillin in plasma, hip capsule, cancellous and ground up bone, and drain fluid that exceed the MICs of these antibiotics against Staph. aureus and E. coli. 6. The plasma, hip capsule, cancellous and ground up bone concentrations of ampicillin after this dose of Magnapen do not, however, exceed the MICs of the Gram negative anaerobes that sometimes cause postoperative wound infections in these patients.

Aged↗
PubMed1977

Pharmacokinetics of salicylate and indomethacin in coeliac disease.

The plasma concentrations of salicylate and indomethacin were measured after a single oral dose of aspirin (600 mg) and indomethacin (50 mg) in twelve starved normal subjects and twelve adult patients with coeliac disease. The absorption of salicylate in the coeliac patients was faster than in the normal subjects. The plasma concentration/time curve of indomethacin in both groups was similar during the absorption phase, but there were significant differences between the groups in its elimination. The abnormal absorption pattern of salicylate in coeliac disease does not appear to be related to its pKa. Possible causes of the difference in salicylate absorption include changes in gastric emptying or altered small intestinal permeability.

Adult↗
PubMed1977

Desensitization and recovery at the frog neuromuscular junction.

The time course of carbachol-induced desensitization onset and recovery of sensitivity after desenitization have been compared at the frog neuromuscular junction. The activation-desensitization sequence was determined from input conductance measurements using potassium-depolarized muscle preparations. Both desensitization onset and recovery from desensitization could be adequately described by single time constant expressions, with tauonset being considerably shorter than taurecovery. In nine experiments, tauonset was 13+/-1.3 s and taurecovery was 424+/-51 s with 1 mM carbachol. Elevating the external calcium or carbachol concentration accelerated desensitization onset without changing the recovery of sensitivity after equilibrium desensitization. Desensitization onset was accelerated by a prior activation-desensitization sequence to an extent determined by the recovery interval that followed the initial carbachol application. The time course of return of tauonset was closely parallel to, but slower than the time course of recovery of sensitivity. These results are consistent with a cyclic model in which intracellular calcium is a factor controlling the rate of development of desensitization.

Animals↗
PubMed1977

Pharmacokinetics of pivmecillinam.

1 The plasma concentration/time curves of ampicillin and mecillinam in normal subjects were measured after oral administration of ampicillin (500 mg) and pivmecillinam (400 and 600 mg). 2 Similar plasma concentration/time curves of ampicillin and mecillinam in the starved normal subjects followed oral administration of ampicillin (500 mg) and pivmecillinam (600 mg). 3 The plasma concentration/time curve of mecillinam was measured in the same normal subjects after oral administration of pivmecillinam (400 mg) with a reproducible standardized Lundh test meal. 4 There was no statistically significant difference in the plasma concentration/time curve of mecillinam after pivmecillinam/400 mg) and the meal compared with the plasma concentration/time curve after oral pivmecillinam (400 mg) was given to the same subjects when starved. After administration of pivmecillinam (400 mg) with meal, Tasc was significantly delayed beyond the value obtained when the subjects were starved. 5 The pharmacokinetics of pivmecillinam in coeliac disease are normal. This finding contrasts with previous studies on the pharmacokinetics of another pivaloyloxymethylpenicillin ester, pivampicillin, in this condition.

Adolescent↗
PubMed1977

Plasma, bone, hip capsule, synovial and drain fluid concentrations of lincomycin during total hip replacement.

1 Lincomycin (600 mg) was given 6 h preoperatively by intramuscular injection, as an intravenous infusion over 30 min and for 72 h postoperatively in twelve patients having total hip replacement. 2 The plasma, bone, hip capsule, synovial and drain fluid concentrations of lincomycin were almost always above the M.I.C. of lincomycin against penicillinase producing Staphylococcus aureus. 3 There was a good correlation between the estimated concentrations of lincomycin in bone by the grinding and agitation methods of analysis. 4 Two patients developed pseudomembranous colitis after parenteral lincomycin.

Adult↗
PubMed1976

Colitis and diarrhoea: a problem with antibiotic therapy.

During a 19-month study the incidence of diarrhoea and colitis was estimated in 1158 orthopaedic inpatients admitted to the Guy's group of hospitals. The highest incidence of diarrhoea followed the use of lincomycin (22.2 per cent), ampicillin with cloxacillin (17.2 per cent), clindamycin (15.3 per cent) and combined therapy with cloxacillin and tetracycline (12.5 per cent). There were 3 documented cases of colitis; 2 followed lincomycin and 1 clindamycin. The incidence and relationship of antibiotic-related diarrhoea and colitis to possible aetiological factors are discussed. In orthopaedic inpatients, in whom lincomycin and clindamycin are often the antibiotics of choice, their continued use appears to be fully justified by the low incidence of colitis. However, if a patient receiving treatment with either of these antibiotics does develop diarrhoea, the antibiotic should be discontinued immediately, to reduce the risk of subsequent colitis.

Adolescent↗
PubMed1976

Antibiotics in bone.

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Anti-Bacterial Agents↗
PubMed1976

Effect of ionophore X-537A on desensitization rate and tension development in potassium-depolarized muscle fibres.

The effects of the ionophore X-537A were studied on carbamylcholine (carbachol)-induced densitization and on tension development in relaxed potassium-depolarized frog sartorius muscles. 2 X-537A accelerated carbachol-induced desensitization in Ca2+-deficient solutions without having any effect on the conductance of the membrane in the absence of carbachol or on the extent of the carbachol-induced increase in conductance. 3 In Ca2+-deficient solution, the acceleration of desensitization by the ionophore was concentration-dependent. No effect was observed with concentrations less than 5 muM and maximal acceleration was evident with 10 muM. 4 The influence of X-537A on desensitization was time-dependent. At 20 muM X-537A, there was a marked acceleration of desensitization by the end of 5 min exposure. An additional gradual acceleration occurred during a 5 to 30 min treatment. No acceleration of desensitization was evident when X-537A was simultaneously applied with carbachol to the end-plate region without prior exposure to the ionophore. 5 Desensitization also was accelerated by 30 min exposure to 20 muM X-537A in solutions containing Ca2+ or deficient in both Mg2+ and Ca2+; the rate being increased 2.8-fold in Ca2+-containing solutions, 2.9-fold in Ca2+-deficient solutions containing Mg2+, and 2.5-fold in divalent cation-deficient solutions. 6 Tension development gradually occurred in relaxed potassium-depolarized muscle preparations exposed to 20 muM X-537A. The onset of tension development occurred only after approximately 25 min of exposure both in preparations kept in Ca2+-deficient or Ca2+-containing solutions. By the end of 90 min in the ionophore, the tension developed was approximately 12% and 23% of the initial potassium contracture in those preparations maintained in the Ca2+-deficient or Ca2+-containing solutions, respectively. 7 We assume that the increase in desensitization rate following exposure to X-537A results from an elevation of the intracellular Ca2+ concentration. That muscle tension gradually increased during exposure to the ionophore supports this conclusion. The acceleration of densitization by X-537A in the absence of external Ca2+ supports the view that the site of calcium acceleration is not on the external surface of the end-plate membrane either at or near the agonist-recognition site but rather on the inner surface.

Animals↗