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Biomedical subjects

P Mason

Publications and source records attributed to P Mason.

At least 181 records · Page 10Linked to original sources
PubMed1978

A rapid and inexpensive laser nephelometric assay for plasma pregnancy specific beta1-glycoprotein levels.

A laser neophelometric method for the measurement of maternal plasma pregnancy specific beta1-glycoprotein levels is described. Fifty plasma specimens can be analysed within four hours at a low reagent cost. The assay has been used to determine the range of plasma pregnancy specific beta1-glycoprotein concentrations in 212 normal pregnancies of from 31 to 41 weeks gestation.

Beta-Globulins↗
PubMed1978

Muscle crossbridge stroke and activity revealed by optical diffraction.

Optical diffraction measurements during rapid releases of active toad muscle show that the sarcomeres contract within 1 millisecond by an amount up to but not greater than 12 nanometers. This crossbridges immediately start cycling to produce the normal contraction velocity in unloaded muscle.

Animals↗
PubMed1978

Pulse propagation in muscle.

A technique is described for measuring the propagation velocity of a mechanical pulse along a muscle. The pulse is generated and detected by piezoelectric crystals (bimorph benders). Measurement of the time delay for a known crystal separation gives the propagation velocity v (of the order of 100 m s-1) from which the Young's modulus is calculated. Primary results for elastic moduli of frog and toad muscles at 5 degrees C are: 2.6 X 10(6) N m-2 at rest, 3.1 X 10(7) N m-2 in tetanus and 2.1 X 10(7) N m-2 in rigor. Exploratory experiments are also described showing the application of the technique to (i) the development of tetanus, (ii) variation with sarcomere length and (iii) the mechanics of rigor. The pulse technique gives an almost instantaneous measurement of the purely elastic response of a muscle and is thereby of value in basic studies of the mechanism of contraction. It is also a useful non-destructive probe in following the effects of such variables as temperature, fatigue or chemical treatments.

Animals↗
PubMed1977

Dynamic stiffness and crossbridge action in muscle.

Small sinusoidal vibrations at 300 HZ were applied to frog sartorius muscle to measure the dynamic stiffness (Young's modulus) throughout the course of tetanus. For a peak-to-peak amplitude of 0.4% the dynamic Young's modulus increased from 1.5 X 10(5) Nm-2 in the resting state to 2 X 10(7) Nm-2 in tetanus. After correction for the external connective tissue, the dynamic Young's modulus of the muscle was almost directly proportional to the tension throughout the development of tetanus. The ratio of dynamic Young's modulus to tensile stress thus remained constant (with a value at 300 Hz of approximately 100), consistently with Huxley and Simmon's identification of the crossbridges as the source of both tension and stiffness. For a single crossbridge the ratio of stiffness to tension was 8.2 X 10(7) m-1 at 300 Hz; it is deduced from literature data that the limiting value at high frequencies is about 1.6 X 10(8) m-1. This ratio is interpreted on Harrington's (1971) model to show that crossbridge action can be explained by a helix-coil transition of about 80 out of the 260 residues in each S-2 myosin strand. It is also shown that a helix-coil model can account for the observed rapid relaxation of muscle without invoking any complex behaviour of the crossbridge head.

Animals↗
PubMed1977

Urine electrolyte response to 18-hydroxy-11-deoxycorticosterone in normal man.

1. To assess whether the adrenal corticosteroid 18-hydroxy-11-deoxycorticosterone [18-(OH)-DOC] affects urine electrolyte excretion in normal man, seven male volunteers received 120 microgram (353 nmol) intravenously in 1 h. This was compared with glucose (50 g/l; control) and aldosterone (80 microgram, 222 nmol) infusions in the same subjects. 2. A definite though weak antinatriuretic response to 18-(OH)DOC was observed, whereas urine potassium excretion was not altered. Aldosterone increased urine potassium excretion and reduced sodium output. Urine pH was lowered by both corticosteroids, aldosterone in general having a more marked effect. Urine volume was not altered by 18-(OH)DOC. 3. Plasma concentrations of 18-(OH)DOC and aldosterone rose approximately tenfold during their respective infusions. Compared with that of aldosterone, the metabolic clearance rate of 18-(OH)DOC was slower andits plasma half-life was longer. 4. We have been able to demonstrate that 18-(OH)DOC has a definite, albeit weak antinatriuretic action in normal man, but whether or not this corticosteroid is capable of elevating the blood pressure in man remains to be shown.

18-Hydroxydesoxycorticosterone↗
PubMed1976

Sarcomere length changes during stimulation of frog semitendinosus muscle.

A method is described for detecting rapid changes in sarcomere length at different points along a muscle specimen during stimulation. Reproducible differences in behaviour are observed at different positions along the length of the muscle both during contraction and during relaxation. By summing individual observations made at points closely spaced along the specimen it is found that in tetanus at 6 degrees C the average sarcomere contraction is about 5% for an initial length of 2.6 mum; a maximum rate of contraction of about 4 nm.ms-1 (0.16% ms-1) is reached and maintained for some 10 ms during the development of tension. In twitch the corresponding values are 4% and 3 nm.ms-1 (0.12% ms-1).

Animals↗