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Biomedical subjects

R H Abbott

Publications and source records attributed to R H Abbott.

14 recordsLinked to original sources
PubMed1984

A possible mechanism of length activation in insect fibrillar flight muscle.

When insect fibrillar flight muscle is stretched it becomes more active, as indicated by an increase in oscillatory work output and ATPase activity. Using glycerol-extracted muscle it is demonstrated that this effect is periodic with a repeat of around 3% length change, independent of temperature and ionic strength. This corresponds to 38 nm per half sarcomere, the same repeat as the actin helix. Since there is also a period of 38 nm in the myosin helix the periodic change of activity with muscle length could be caused by filament sliding. This may be the basis of the mechanism of length activation.

Actins↗
PubMed1981

Biochemical interpretation of tension transients produced by a four-state mechanical model.

We have simulated transient tension responses seen in rabbit psoas and insect flight muscle using a four-state cycle. A wide range of all the rate constants in the cycle and a minimum number of simple mechanical assumptions were used. The rate constants were noted for those cases in which the transient resembled a response seen in real muscle and in which the values of ATP turnover were realistic. The rate constants fell within narrow ranges. With a suitable correspondence of mechanical and biochemical state the actual rate constants were compatible with those determined in biochemical experiments. It was possible to model the effects of temperature, calcium ion concentration, length change and the removal of inorganic phosphate.

Actomyosin↗
PubMed1977

Temperature and amplitude dependence of tension transients in glycerinated skeletal and insect fibrillar muscle.

1. Quick stretches and releases were applied to small bundles of glycerinated fibres of rabbit psoas and insect fibrillar flight muscle. The resulting tension changes were recorded at various temperatures and amplitudes of length change. The results from the two preparations had many features in common. At temperatures near 0 degrees C the asymmetry of the initial tension recovery after stretch and release originally reported in living frog fibres by Huxley & Simmons (1971 alpha) was very obvious. 2. The complete tension course could be described as an elastic change occurring simultaneously with the length change followed by recovery consisting of the sum of a number of exponential terms. These terms usually corresponded to the phases discernible without curve fitting, but in some cases a monotonic rise or fall of tension was seen to consist of two components only after curve fitting. 3. After either stretch or release there was a phase of rapid tension recovery towards the value before the length change. The rate constant of this phase increased as the amplitude of stretch or release was increased to about 2 nm/half sarcomere. At higher amplitudes it remained nearly constant 4. At temperatures near 0 degrees C there was a second and much slower continuation of the recovery after stretch. The rate constant of this second phase was much more sensitive to temperature than that of the first phase and it became slower with increasing amplitude of stretch. As the temperature was raised the speed of the second phase approached the speed of the first phase so that at room temperatures the initial tension recovery after stretch and release was nearly symmetrical. 5. Under many conditions these processes were followed by a change in the opposite direction, the 'delayed tension' described by earlier workers. This third phase of tension change had about the same temperature sensitivity as the second phase of the recovery seen after stretch. The tension due to stretch activation was not maintained in rabbit muscle, resulting in a fourth possible phase, a recovery of tension towards the value before the length change. This was absent or of low amplitude in insect flight muscle. 6. We interpret these tension changes on the basis of an extension of the non-linear model described by White & Thorson (1972). The elastic tension change and the initial fast recovery are both supposed to be properties of the attached cross-bridges, whilst the slower recovery is considered to be due to the detachment of cross-bridges which happened to be attached at the instant the length change was applied. The delayed tension reflects the approach to equilibrium of the number of attached bridges, changed by an effect of muscle length on the attachment rate. The fact that the delayed tension is not maintained in rabbit psoas muscle may be due to the effect of length on attachment rate being transitory.

Animals↗
PubMed1973

The effects of fibre length and calcium ion concentration on the dynamic response of glycerol extracted insect fibrillar muscle.

1. The property of insect fibrillar muscle which enables it to oscillate continuously when it is connected to a resonant load is the delayed activation by stretch of contractile activity. The dynamic response has been measured at different fibre lengths and at different calcium ion concentrations, to see what effects these conditions have on the magnitude and rate constant of the delayed tension.2. Bundles of ten fibres of the dorsal longitudinal muscle of the water bug, Lethocerus cordofanus, which had been in glycerol for less than 5 days were used. Graded activation was obtained with buffered calcium ion concentrations between 10(-7) and 10(-5)M.3. A computer-controlled apparatus was used to measure the dynamic mechanical properties of the muscle fibres. This allowed many measurements to be made on the same preparation. Further computer programs analysed the Nyquist plots produced by the experiment.4. When the mean length of a fibre bundle was increased, the magnitude of the delayed tension was increased (for a constant amplitude of sinusoidal length change), the rate constant was unaltered, and the stiffness of the fibres was increased. When the calcium ion concentration was raised, the magnitude of the delayed tension was increased, the rate constant increased, and the stiffness of the fibres fell. Calcium activation and stretch activation are thus clearly separable in their effects, and so the mechanisms must be separate.5. The various different effects of calcium cannot be explained by any simple model of activation, for example, an on-off switch mechanism controlling the number of bridges in action.6. The stretch-induced activity is proportional to a power of the length of two or greater and this non-linearity aids the efficient operation of the oscillatory mechanism.

Animals↗