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Biomedical subjects

A R Luff

Publications and source records attributed to A R Luff.

At least 55 records · Page 3Linked to original sources
PubMed1982

Contractile properties of hindlimb muscles in rat during surgical overload.

Structural and dynamic properties of the extensor digitorum longus (EDL) and soleus muscles of the rat under pentobarbital sodium anesthesia have been determined 4, 28, and 400 days after extirpation of the tibialis anterior and compared with the properties of muscles from the contralateral limb of the same animal. At 4 days the mass of the EDL increased by about 17%, but the maximum tetanic tension and tension per unit cross-sectional area decreased. The soleus showed a slight decrease in mass of about 6%. At 28 days the mass of the EDL had increased to 126% of the control value. Maximum isometric twitch and tetanic tensions increased, whereas tetanic tension per unit cross-sectional area returned to normal values; the number of sarcomeres in series increased, which led to an increase in the whole muscle speed of shortening. It is concluded that the synergistic EDL undergoes compensatory hypertrophy by the addition of contractile material in series and in parallel but without any change in the intrinsic properties of the muscle. The fibers of the antagonistic soleus shorten slightly but are otherwise unchanged.

Animals↗
PubMed1981

Dynamic properties of the inferior rectus, extensor digitorum longus, diaphragm and soleus muscles of the mouse.

1. Isometric responses to direct stimulation of inferior rectus (IR), extensor digitorum longus (EDL) and soleus (SOL) muscles and strips of diaphragm (DIA) muscle of the mouse were obtained. 2. The IR, EDL and DIA were qualitatively 'fast-twitch', while the SOL was 'slow-twitch'. The isometric twitch contraction time was for IR, 3.7 ms; EDL, 6.9 ms; DIA, 13.2 ms; SOL, 20.9 ms (at 35 degrees C). Twitch: tetanus ratio for IR was unusually small (0.12) whereas that of DIA was unusually large (0.31). 3. The force-velocity properties of the muscles were determined and the sarcomere speed of shortening calculated. The intrinsic speeds of shortening of EDL and IR were not significantly different from each other, and were 49.5 and 51.6 micrometers . s-1 respectively; the value for SOL was 23.1 micrometers . s-1 and the DIA was intermediate at 39.7 micrometers . s-1. 4. The time course of the isometric twitch of the IR was about half that of the EDL whereas the force-velocity properties of these two muscles were almost identical. This is very similar to the situation in the rat. 5. Some of the dynamic properties of the DIA were clearly intermediate between the typical 'fast-twitch' EDL and IR and the typical 'slow-twitch' SOL. This does not agree with the available histochemical evidence which suggests that the mouse diaphragm is a 'fast-twitch red' muscle.

Animals↗
PubMed1979

Properties of motor units of the frog iliofibularis muscle.

The tension developed by single motor units of the iliofibularis muscle of the frog Litoria aurea was recorded in response to single-shock and repetitive stimulation of motor axons. The majority of units in each muscle, 13 on the average, were of the twitch type; an additional 4 units were slow or tonic. It appeared that slow units comprised a single homogeneous population, but two types of twitch units could be recognized: small fatigue-resistant units with long twitch times to peak (20--40 ms) and larger, fatigable units with briefer times to peak (16--27 ms). Evidence from a comparison of unit tetanic tensions indicated the presence of polyneuronal innervation of both slow and twitch muscle fibers. The relatively low incidence of polyneuronal innervation of twitch fibers in iliofibularis, when compared with a muscle like sartorius (9), was attributed to the difference in lengths of muscle fibers in the two muscles. It was argued that slow muscle fibers probably receive a multiterminal as well as polyneuronal innervation, with the terminals of any one axon lying widely spaced along the muscle fiber.

Animals↗
PubMed1978

The stiffness of amphibian slow and twitch muscle during high speed stretches.

Experiments were carried out to compare the stiffness of cross-bridges in amphibian slow and twitch muscle. An isolated iliofibularis muscle was subjected to rapid, small stretches during contraction of either slow or twitch fibres at a number of different isometric tensions. The method of analysis allowed the compliance of the cross-bridges to be distinguished from other sources of compliance. Provided that the muscle was stretched sufficinetly rapidly to obtain limiting values of stiffness, little difference was found between the mechanical properties of the cross-bridges in slow and twitch muscle. It is concluded that the difference in observed stiffness of the two muscle types is due to a lower turnover rate of cross-bridges and a smaller number of sarcomeres in slow fibres.

Animals↗
PubMed1976

Properties of motor units of the frog sartorius muscle.

1. The mechanical properties of single motor units in the sartorius muscle of the frog Litoria aurea were examined during single shock and repetitive stimulation of motor axons. 2. The tetanic tension developed by motor units lay in the range 1-40% of whole muscle tension with two peaks in the distribution, in the range 5-10% and 25-30%. The large units had briefer times-to-peak for the twitch than the small units and were more readily fatigued during prolonged repetitive stimulation. 3. Histological examination of the muscle gave a count of 620 muscle fibres with a diameter range of 28-128 mum. Cholinesterase stained preparations showed that the majority of muscle fibres had several nerve terminals (mean 3, range 1-5). 4. Muscle fibres received their multiple innervation from different axons (polyneuronal) or branches of the same axon (multiterminal). The presence of polyneuronal innervation of muscle fibres was confirmed by a comparison of the tensions when each of a pair of motor units was stimulated alone and when they were stimulated together. The tension excess, or overlap, was up to 60% when expressed in terms of the tension developed by either unit alone. Motor units developing similar amounts of tension tended to show more overlap in their innervation than units with very different tensions. 5. An estimate of the amount of multiterminal innervation gave variable results but could account for up to 60% of a motor unit's tension. No correlation could be detected between the values for multiterminal innervation and any other measured parameter. However, it is argued that because of the limitations of the measurements the existence of a relationship between the extent of multiterminal or polyneuronal innervation and the mechanical properties of the motor unit cannot be excluded.

Action Potentials↗
PubMed1975

Effect of cross-reinnervation on physiological parameters and on properties of myosin and sarcoplasmic reticulum of fast and slow muscles of the rabbit.

Cross-reinnvervation of fast (extensor digitorum longus) and slow (soleus) twitch muscles of the rabbit showed essentially complete fast to slow and slow to fast conversion, respectively, 11-12 mo after surgery with respect to a number of physiological parameters including intrinsic shortening, velocity, and isometric twitch time to peak. There was pronounced bu incomplete biochemical conversion as judged by Ca2+ uptake by sarcoplasmic reticulum, myosin ATPase, alkali lability, and light chain complement. The question of trophic substances of neural origin is discussed in light of the fact that chronic stimulation for 15 wk of a fast muscle produces complete biochemical and physiological conversion to the slow type.

Adenosine Triphosphatases↗
PubMed1975

Dynamic properties of fast and slow skeletal muscles in the cat and rat following cross-reinnervation.

1. Cross-reinnervation was performed between the slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles in the cat and the SOL and fast-twitch flexor hallucis longus (FHL) muscles in the rat. The isometric and force-velocity properties of the muscles were subsequently determined. 2. As a result of cross-reinnervation the dynamic properties of both slow- and fast-twitch muscles in the cat were considerably altered. The isometric twitch time to peak was 33-9 msec in the X-SOL compared with 84-7 msec in the N-SOL. The intrinsic speed of shortening and a/P0 values were 25-4 mum. sec-1 and 0-34 respectively in the X-SOL and 14-4 mum. sec-1 and 0-20 in the N-SOL. In the X-EDL the twitch time to peak was 52-6 msec compared with 23-4 msec in the N-EDL; the intrinsic speed of shortening and a/P0 values were 14-1 mum. sec-1 and 0-29 respectively, whereas they were 31-9 mum. sec-1 and 0-44 in the N-EDL. 3. In the rat X-SOL there was shortening of the isometric twitch time to peak from 39-5 msec in the N-SOL to 19-7 msec and an increase in the intrinsic speed of shortening from 17-7 mum. sec-1 to 32-3 mum. sec-1, although over most of the force-velocity curve the X-SOL values were only slightly greater than those for N-SOL. The force-velocity data for the X-SOL muscles could not be fitted by Hill's equation. 4. The isometric and force-velocity results of the X-SOL of the rat suggested that the muscle contained a significant proportion of slow fibres. An examination of the motor unit characteristics of the N-FHL showed the presence of approximately 14% small, slow units. 5. It is concluded that there are no fundamental differences between the rat and the cat with regard to the effect of cross-reinnervation on hind-limb muscles. However, these, and previously published results, suggest that there may be important differences between heterologous muscles in the degree of influence that their respective motor nerves can exert on an alien muscle.

Animals↗
PubMed1974

Dynamic properties of inferior rectus muscle of the rat.

1. Isometric responses of rat inferior rectus muscle to indirect and direct stimulation were compared, and conditions were found for selective direct stimulation of twitch fibres in vitro.2. Most of the twitch fibres were qualitatively ;fast'.3. The influence of length on isometric contractions and the relation between relative load and speed of sarcomere shortening of fast-twitch fibres were determined.4. The isometric twitch contraction and half-relaxation times of fast-twitch inferior rectus fibres were only about one half of those of rat extensor digitorum longus fibres in the same conditions, whereas the force: velocity properties of these two fibre groups were virtually the same. These results show that the relation between intrinsic speed of shortening and duration of the active state of the contractile material is not the same for rat extraocular and hind-limb muscles.

Journal Article↗
PubMed1971

Changes in the sarcoplasmic reticulum and transverse tubular system of fast and slow skeletal muscles of the mouse during postnatal development.

The sarcoplasmic reticulum (SR) and transverse tubular system (TTS) of a fast-twitch muscle (extensor digitorum longus-EDL) and a slow-twitch muscle (soleus-SOL) of the mouse were examined during postnatal development. Muscles of animals newborn to 60 days old were fixed in glutaraldehyde and osmium tetroxide and examined with an electron microscope. At birth the few T tubules were often oriented longitudinally, but at the age of 10 days most of them had a transverse orientation. In the EDL, the estimated volume of the TTS increased from 0.08% at birth to 0.4% in the adult; corresponding values for the SOL were 0.04% at birth and 0.22% in the adult. A similar relative change was observed in surface area of the TTS during development. Calculated on the basis of a 30 microm diameter fiber, the surface area of the TTS in the EDL increased from 0.60 cm(2) TTS/cm(2) fiber surface in the newborn to 3.1 cm(2)/cm(2) in the adult, compared with 0.15 cm(2)/cm(2) at birth to 1.80 cm(2)/cm(2) in the adult for the SOL. The SR in the newborn muscles occurred as a loose network of tubules that developed rapidly within the subsequent 20 days, especially at the I band level. The volume of the SR increased in the EDL from 1.1% of fiber volume at birth to 5.5% in the adult. In the SOL the change was from 1.7% to 2.9%. The SOL approached the adult values more rapidly than the EDL, although the EDL had more SR and T tubules. Fibers of both EDL and SOL muscles showed variation in Z line thickness, mitochondrial content, and diameter, but over-all differences between the two muscles in amount of SR and TTS were significant. It is considered that the differing amounts of SR and TTS are closely related to the differing speeds of contraction that have been demonstrated for these two muscles.

Age Factors↗