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Biomedical subjects

M Irving

Publications and source records attributed to M Irving.

At least 19 recordsLinked to original sources
PubMed1992

Myosin head movements are synchronous with the elementary force-generating process in muscle.

Motor proteins such as myosin, dynein and kinesin use the free energy of ATP hydrolysis to produce force or motion, but despite recent progress their molecular mechanism is unknown. The best characterized system is the myosin motor which moves actin filaments in muscle. When an active muscle fibre is rapidly shortened the force first decreases, then partially recovers over the next few milliseconds. This elementary force-generating process is thought to be due to a structural 'working stroke' in the myosin head domain, although structural studies have not provided definitive support for this. X-ray diffraction has shown that shortening steps produce a large decrease in the intensity of the 14.5 nm reflection arising from the axial repeat of the myosin heads along the filaments. This was interpreted as a structural change at the end of the working stroke, but the techniques then available did not allow temporal resolution of the elementary force-generating process itself. Using improved measurement techniques, we show here that myosin heads move by about 10 nm with the same time course as the elementary force-generating process.

Actins↗
PubMed1992

Appraisal of percutaneous tracheostomy.

Two commercially available kits have been used to create 25 percutaneous tracheostomies, 20 using the Cook system and five using the Rapitrac system. The operation time and complication rates of these tracheostomies have been compared with those for 16 conventional tracheostomies performed for similar indications. Median operating times were 60 (range 30-105) min for conventional tracheostomy, 15 (range 8-70) min for Cook and 5 (range 3-15) min for Rapitrac systems (P less than 0.001). A significantly higher proportion of patients in the Rapitrac group had complications compared with the other two groups (P less than 0.05). The complication rate for the Cook group compared favourably with that for the conventional tracheostomy group. The Cook system of percutaneous tracheostomy is a simple, rapid and safe alternative to conventional tracheostomy.

Adult↗
PubMed1991

Surgeons and HIV.

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AIDS Serodiagnosis↗
PubMed1991

Hepatic phosphofructokinase-1 activity and fructose 2,6-bisphosphate levels in patients with abdominal sepsis.

1. In sepsis various processes of carbohydrate metabolism, such as hepatic gluconeogenesis and glycolysis, are altered. Phosphofructokinase-1, a key glycolytic enzyme, is controlled in the long term via regulation of synthesis and degradation of the protein itself, while in the short term it is regulated by allosteric effectors, such as fructose 2,6-bisphosphate (the most potent). In the present study hepatic phosphofructokinase-1 activity as well as phosphofructokinase-2 activity and the concentration of fructose 2,6-bisphosphate were assayed to determine if they might contribute to the derangement of carbohydrate metabolism seen commonly in sepsis. 2. The levels of glycogen and fructose 2,6-bisphosphate and the activity of phosphofructokinase-1 and phosphofructokinase-2 were determined in hepatic biopsies obtained at laparotomy from six patients with and seven patients without abdominal septic foci. 3. A significant increase in plasma lactate concentration was observed in the septic patients, whereas no significant differences in tissue glycogen content or plasma glucose concentration were seen between the groups. 4. No significant change in plasma insulin concentration was observed. However, levels of the counter-regulatory hormones (glucagon, cortisol and adrenaline) were elevated in the septic patients. 5. A 60% decrease in hepatic phosphofructokinase-1 activity was seen in the septic patients. However, no significant changes in hepatic phosphofructokinase-2 activity and fructose 2,6-bisphosphate content were observed in the septic patients. 6. The present results demonstrate that the decrease in hepatic phosphofructokinase-1 activity occurring in sepsis does not appear to reflect alterations in the concentration of fructose 2,6-bisphosphate.

Abdomen↗
PubMed1990

Intracellular diffusion in the presence of mobile buffers. Application to proton movement in muscle.

Junge and McLaughlin (1987) derived an expression for the apparent diffusion constant of protons in the presence of both mobile and immobile buffers. Their derivation applies only to cases in which the values of pH are considerably greater than the largest pK of the individual buffers, a condition that is not expected to hold in skeletal muscle or many other cell types. Here we show that, if the pH gradients are small, the same expression for the apparent diffusion constant of protons can be derived without such constraints on the values of the pK's. The derivation is general and can be used to estimate the apparent diffusion constant of any substance that diffuses in the presence of both mobile and immobile buffers. The apparent diffusion constant of protons is estimated to be 1-2 x 10(-6) cm2/s at 18 degrees C inside intact frog twitch muscle fibers. It may be smaller inside cut fibers, owing to a reduction in the concentration of mobile myoplasmic buffers, so that in this preparation a pH gradient, if established within a sarcomere following action potential stimulation, could last 10 ms or longer after stimulation ceased.

Action Potentials↗
PubMed1979

Seat-belts.

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Legislation as Topic↗
PubMed1979

A safe and effective disposable low pressure suction drain.

The physical and microbiological properties of a new disposable suction drainage system have been investigated under clinical and laboratory conditions. The system appears to have overcome the disadvantages associated with previous disposable and reusable low pressure suction drainage systems for use after surgical operation in that this system effectively prevents reflex and retrograde contamination.

Bacteria↗
PubMed1979

The heat produced by frog muscle in a series of contractions with shortening.

1. Heat production has been measured in muscles undergoing rapid shortening 1 sec after the start of stimulation in a 2 sec tetanus. In a series of three such tetani where the periods of shortening were separated by 5 sec the shortening heats in the second and third tetani were 111 (+/- 4)% and 116 (+/- 6)% respectively of that in the first tetanus (mean +/- S.E. of mean, nine experiments). 2. When a similar series was carried out after an interval of 3 min the shortening heat in the first tetanus of the second series was 127 (+/- 3)% of that in the first tetanus of the first series (mean +/- S.E. of mean, three experiments). 3. The results are not in agreement with those of Dickinson & Woledge (1974). The discrepancy is explained by an artifact which, with certain arrangements of the apparatus, affects the measurements of shortening heat in a series of contractions. We have measured this artifact by two independent methods; the shortening heat values quoted above have been corrected accordingly. 4. The increase in the shortening heat in repeated contractions is not a specific consequence of previous shortening; an increase of the same magnitude is observed following isometric tetani. 5. During the time when the muscle is shortening, the total rate of heat production, which is initially high, falls to a steady value. This value is not significantly different in the three tetani of the series.

Animals↗
PubMed1977

Ulcerative colitis.

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Colitis, Ulcerative↗