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Biomedical subjects

J F Hoh

Publications and source records attributed to J F Hoh.

53 records · Page 3Linked to original sources
PubMed1977

Myosins in murine muscular dystrophy.

Electrophoresis of intact myosin ATPases extracted from fast-twitch and slow-twitch muscles of dystrophic mice, and from control mice, was performed. The proportions of the lower ATPase myosin were increased in the dystrophic muscles. These results correlated with the abnormalities in the isometric myogram and the force/velocity relationships which have been described.

Adenosine Triphosphatases↗
PubMed1975

Neural regulation of mammalian fast and slow muscle myosins: an electrophoretic analysis.

Mammalian nerves to fast and slow muscles have the remarkable property of changing the speed of contraction of muscles following cross-reinnervation. The biochemical basis of speed transformation is the change in myosin in ATPase activity. This paper provides electrophoretic evidence for structural changes in myosin from cross-reinnervated muscles. A method is described for the separation of intact fast and slow muscle myosins by polyacrylamide gel electrophoresis. This method utilizes the fact that ATP and its analogs prevent the formation of myosin polymers in low ionic strength buffers. In this system, normal fast muscle myosin has a higher electrophoretic mobility than slow muscle myosin. Normal rat soleus myosin has a major slow and a minor fast component due to two populations of muscle fibers. The same muscle cross-reinnervated by a fast muscle nerve shows only the fast component, The normal, homogeneous fast extensor digitorum longus muscle has only the electrophoretically fast myosin, but following cross-reinnervation it shows both fast and slow components. These results suggest that mammalian motor nerves can induce or suppress the expression of genes that code for fast and slow skeletal muscle myosins.

Adenosine Triphosphatases↗
PubMed1975

Selective and non-selective reinnervation of fast-twitch and slow-twitch rat skeletal muscle.

1. The problem of selectivity during reinnervation of skeletal muscle fibres was investigated in the rat using the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus muscles and their nerves. 2. After an operation on these nerves permitting them to compete for reinnervation of one or the other muscle (hereafter called Y-union), virtually the total isometric tetanic tension of EDL muscle could be elicited by stimulating the EDL nerve, while stimulating the soleus nerve yielded little or no tension. In the case of the soleus muscle, stimulation of either nerve elicited about half of the total isometric tetanic tension. 3. During the course of reinnervation of these muscles in non-competitive situations, the time course of increase in the ratio of tension elicited by nerve stimulation to that by direct stimulation was slower in the case of soleus nerve reinnervating EDL muscle, compared with cross-reinnervation in the reverse direction or reinnervation of each muscle by its own nerve. 4. Crushing the common peroneal nerve 12 days after a Y-union in an attempt to retard the EDL nerve did not favour reinnervation of the EDL by soleus nerve, but crushing the nerve again or just once at 1 month after the original operation produced substantial partial reinnervation of the EDL by the soleus nerve. 5. It is concluded that soleus nerve fibres form functioning neuromuscular synapses on EDL muscle fibres only with difficulty. The pattern of reinnervation reveals characteristic differences between fast-twitch and slow-twitch muscles on the one hand and between their respective nerves on the other.

Animals↗
PubMed1971

Effects of nerve cross-union on rat intracellular potassium in fast-twitch and slow-twitch rat muscles.

1. Electrolytes of normal, self-innervated and cross-innervated extensor digitorum longus and soleus muscles of rats have been determined.2. [K](i) was 173 m-equiv/l. for both normal and self-innervated extensor digitorum longus. In cross-innervated extensor digitorum longus it was reduced to 159 m-equiv/l.3. For normal and self-innervated soleus, [K](i) was 150 m-equiv/l. and 154 m-equiv/l. respectively. In cross-innervated soleus it was increased to 182 m-equiv/l.4. The content and distribution of most other electrolytes of cross-innervated soleus, as well as its weight, were not significantly different from those of controls. On the other hand, cross-innervated extensor digitorum longus weighed about half as much as controls and contained markedly elevated Na(+), Cl(-) and extrafibre water and reduced non-collagenous protein and intrafibre water.5. It is concluded that [K](i) of fast-twitch and slow-twitch muscle fibres are under neural regulation. Possible mechanisms for this regulation are discussed.

Animals↗
PubMed1968

The after-effects of repetitive stimulation on the isometric twitch contraction of rat fast skeletal muscle.

1. The peak tension and time course of isometric twitch contractions of rat extensor digitorum longus muscle in vitro (35 degrees C) have been measured at various stages of potentiation following repetitive stimulation at 20 c/s and 300 c/s.2. Potentiation of the peak twitch tension increases with an increase in the number of repetitive stimuli up to a maximal level of about 1.9 times the control value. The relation between potentiation and numbers of stimuli is dependent on the frequency of stimulation.3. Potentiation of peak twitch tension is maximal shortly after the end of repetitive stimulation and subsequently decays exponentially at a rate which is dependent on the number of stimuli in the train and the frequency of stimulation.4. Short trains of stimuli bring about nearly maximal potentiation with little or no change in contraction time and a small decrease in half-relaxation time.5. Long trains of stimuli increase the contraction time, the half-relaxation time and the twitch duration in addition to potentiating the peak tension. The changes in twitch time course are dependent on the number of repetitive stimuli and the frequency of stimulation.6. The results are discussed in relation to possible mechanisms of post-tetanic potentiation and the degree of activation of mammalian and amphibian muscle fibres.

Amphibians↗
PubMed1968

Effects of nerve cross-union on fast-twitch and slow-graded muscle fibres in the toad.

1. A method is described for resolving isometric tetanic tension developed by fast-twitch and slow-graded components of heterogeneous toad muscles. This makes use of the difference in threshold for excitation of low threshold nerve fibres which normally innervate the fast-twitch muscle fibres and high threshold nerve fibres which innervate slow-graded muscle fibres.2. The sartorius muscle contains only fast-twitch muscle fibres whereas the posterior semitendinosus (PST) contains both fast-twitch and slow-graded muscle fibres, the latter contributing 10-15% of the maximum isometric tetanic tension.3. Following surgical cross-union of nerve to sartorius and PST muscles, both the fast-twitch and slow-graded muscle fibre components of the PST are reinnervated by low threshold nerves originally innervating sartorius fast-twitch fibres, and sartorius fast-twitch muscle fibres are reinnervated by both low threshold and high threshold nerves formerly supplying the fast-twitch and slow-graded muscle fibre components of the PST.4. The characteristic mechanical responses of fast-twitch muscle fibres and slow-graded muscle fibres were not transformed up to 134 and 200 days respectively following nerve cross-union.5. PST nerve partially innervated the sartorius muscle whereas sartorius nerves completely innervated the PST muscle. Isometric tetanic tension declined markedly during repetitive indirect stimulation of cross-innervated sartorius muscles, whereas the tetanic contractions of cross-innervated PST showed a plateau of tension and resembled the response of normal muscles.6. Normal, cross-innervated and self-innervated PST muscles gave sustained contractures in the presence of acetylcholine whereas PST muscles denervated for 120 days gave phasic contractures similar to those of normal, cross-innervated and self-innervated sartorius muscles.

Journal Article↗
PubMed1967

Force: velocity pproperties of kitten muscles.

1. The characteristics of isometric contractions and force:velocity properties of the extensor digitorum longus (EDL) and soleus (SOL) muscles of neonatal kittens were determined in situ.2. The mean contraction time is 51 msec for EDL and 70 msec for SOL and the half-relaxation time is 51 msec for EDL and 109 msec for SOL.3. The average maximum isometric tetanic tension per unit cross-sectional area of muscle is 1.27 kg/cm(2) for EDL and 1.17 kg/cm(2) for SOL.4. The average twitch:tetanus ratio is 0.28 for EDL and 0.119 for SOL; the low value for SOL was found for both indirect and direct stimulation.5. The average maximum speed of shortening of a sarcomere is 22.8 mu/sec for EDL and 12.7 mu/sec for SOL.6. These properties of neonatal muscles are compared with those of adult cat muscles and discussed in connexion with differentiation of mammalian muscles into fast and slow types.

Aging↗
PubMedDate not supplied

Embryonic and foetal myosins in human skeletal muscle. The presence of foetal myosins in duchenne muscular dystrophy and infantile spinal muscular atrophy.

Recently described techniques for separating myosin isoenzymes have been adapted for analysis of myosins from diseased and developing human skeletal muscle. The method is highly suitable for analysis of human myosins because only 2 - 3 mg of muscle are required for routine analyses. Human embryonic/foetal myosins are electrophoretically distinct from mature skeletal myosins, and are not normally detected beyond the first month of post-natal life, except in premature infants. They have a high alkaline calcium-activated ATPase activity. This would account for the histochemical classification of foetal fibres as "Type II", although physiological differences between adult fast-twitch muscle and foetal muscle are well recognized. Foetal myosins are also synthesized in human skeletal muscle under certain pathological circumstances. Their presence in Duchenne dystrophy probably reflects the associated marked muscle regeneration, with immaturity of some muscle cells. The large amounts of foetal myosin present in many cases of infantile spinal muscular atrophy is evidence that innervation is necessary for the normal cessation of foetal myosin synthesis.

Animals↗
PubMedDate not supplied

Influence of myosin isoforms on tension cost and crossbridge kinetics in skinned rat cardiac muscle.

1. In attempting to consolidate the role of ventricular isomyosins in regulating the contractility of the myocardium, actomyosin ATPase and crossbridge kinetics were obtained at 24 degrees C in chemically skinned isometrically contracting cardiac muscles containing V1 and V3 isomyosins. 2. The ATPase activity was measured at various levels of Ca2+ activation by the enzymatic coupling of ATP hydrolysis with the conversion of NADH to NAD+. The crossbridge kinetics were inferred from small-amplitude perturbations of muscle length and muscle tension, and characterized by the frequency-domain parameter fmin. 3. The ATPase rates of V1 and V3 muscles obtained at various levels of Ca2+ activation were plotted against the corresponding proportional tensions. The ATPase vs tension plots were linear with slopes of 4.92 nmol/min-1 per mm per mN and 1.98 nmol/min-1 per mm per mN, respectively for, V1 and V3 muscles. Individual calculations of ATPase-to-tension ratios (nmol/min-1 per mm per mN) gave corresponding averages of 4.98 +/- 0.12 (s.e.m., n = 12) and 2.16 +/- 0.12 (s.e.m., n = 10). The myosin isoform induced proportional change in tension cost was accompanied by a similar change in fmin (4.1 +/- 0.1 Hz and 1.95 +/- 0.03 Hz, means +/- s.e.m., for V1 and V3 muscles, respectively). 4. The observations and other published kinetic data are discussed in the context of models of crossbridge cycling. It is suggested that the tension economy of V3 muscle arises principally from an increase in the fraction of time, during the crossbridge cycle, when the crossbridge is exerting force.

Adenosine Triphosphatases↗