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Biomedical subjects

A C Wareham

Publications and source records attributed to A C Wareham.

34 records · Page 2Linked to original sources
PubMed1984

Intracellular activity of sodium in normal and dystrophic skeletal muscle from C57BL/6J mice.

Potassium and sodium ion-selective microelectrodes were used in vitro to investigate the depolarization of skeletal muscle fibers associated with muscular dystrophy. In dystrophy there was a large increase of intracellular Na activity and an associated decrease in K activity in fibers of extensor digitorum longus muscles. Despite this, the recorded membrane potential was very close to the calculated potassium equilibrium potential (Ek) in dystrophic fibers. In contrast, in normal muscle fibers, Em was significantly depolarized with respect to Ek. The data suggest that in dystrophic fibers there is an increase in the relative membrane permeability to potassium over sodium.

Animals↗
PubMed1982

A comparison of the mechanical properties of oesophageal striated muscle with skeletal muscles of the guinea pig.

An in vitro comparative study has been made of the contractile properties of guinea pig oesophageal striated muscle with fast twitch (extensor digitorum longus) and slow twitch (soleus) muscles. Histochemical analysis of sections showed oesophageal fibres to react in a manner typical of fast twitch muscles. Isometric measurements made at 23 and 37 degrees C indicated that oesophageal striated muscle contracts at speeds similar to, but still significantly faster than soleus. Isotonic measurements of oesophageal preparations made at 23 degrees C gave an intrinsic speed of shortening and an a/Po value derived from Hill's equation, comparable with that obtained for soleus. The reason for the contradiction between the results from histochemistry, and the results from isometric and isotonic contractions are not apparent, but may be due to differences in fibre arrangement between oesophagus and the two skeletal muscles.

Adenosine Triphosphatases↗
PubMed1982

Early life undernutrition in rats. 1. Quantitative histology of skeletal muscles from underfed young and refed adult animals.

1. Male rats were undernourished either during the gestational and suckling periods or for a period of time immediately following weaning. Some rats were killed at the end of the period of undernutrition; others were nutritionally rehabilitated for lengthy periods of time before examination. Two muscles, the extensor digitorum longus (EDL) and soleus (SOL) were studied from each rat. Histochemically-stained transverse sections of these muscles were used to determine total number of fibres, the fibre cross-sectional areas and the relative frequency of the various fibre types. 2. All rats killed immediately following undernutrition showed significant deficits in body-weight, muscle weight and fibre cross-sectional area compared to age-matched controls. 3. Animals undernourished during gestation and suckling and then fed normally for 5 months showed persistent and significant deficits in body-weight, muscle weight, muscle weight and total fibre number. There were also significant deficits in mean fibre cross-sectional area of each fibre type except for red fibres in the EDL. No difference in the volume proportion of connective tissue was found. 4. Rats undernourished after weaning and then fed ad lib. for approximately 7 months had normal body-and muscle weights. Their muscles showed no significant differences in total fibre number, relative frequency of the various fibre types, fibre size or volume proportion of connective tissue. 5. These results indicate that, although the effects on rat skeletal muscle of a period of undernutrition after weaning can be rectified, undernutrition before weaning causes lasting deficits.

Age Factors↗
PubMed1982

Early life undernutrition in rats. 2. Some contractile properties of skeletal muscles from adult animals.

1. The contractile properties of soleus and extensor digitorum longus muscles from animals at 12 months of age whose mothers had been undernourished during pregnancy and lactation (PU rats) have been compared with those of muscles from ge-matched controls. 2. Body-weight and muscle wet weight of PU rats was significantly reduced. Muscle:body-weight values were, however, no different from controls. 3. No significant alterations in whole muscle speeds of contraction or relaxation could be detected when compared with those of age-matched controls. 4. Twitch and tetanic forces of both SOL and EDL were greater per unit weight of muscle in PU rats. Apart from SOL twitch these differences were significant. The tetanus:twitch values were, however, not different.

Age Factors↗
PubMed1979

Effects of denervation on resting membrane and action potentials of neonate rat fast and slow twitch muscles.

During the first 20 days postpartum of the rat, a period of rapid muscle growth, resting potentials and maximum rate of rise and overshoot of action potentials recorded from fast and slow twitch muscle fibres all increased, although did not reach adult values. The action potential of fast twitch muscle fibres had a greater maximum rate of rise and overshoot than that of slow twitch muscle fibres of the same age. Innervation had a marked influence upon maintenance of the electrical properties of muscle fibres in the neonate since denervation reduced the value of the resting potential and maximum rate of rise and overshoot of the action potential. Neverthless, some differences between action potentials recorded from the two fibre types remained 4 days after denervation.

Action Potentials↗
PubMed1978

Effect of denervation and ouabain on the response of the resting membrane potential of rat skeletal muscle to potassium.

The effects of denervation and ouabain on the relationship between resting membrane potential (EM) and extracellular potassium concentration were determined for rat soleus (SOL) and extensor digitorum longus (EDL) muscles. At concentrations above 20 mM for both SOL AND EDL fibres the relationship could be described adequately by the Nernst equation. Denervation resulted in reduction of EM and a decrease in the slope of the relationship between EM and potassium concentration. 10(-3) M ouabain produced the same effects as denervation. The results are discussed in relation to the alterations in membrane permeability previously shown to occur as a consequence of denervation. It is concluded that the low EM of denervated muscle is the result of an increase in membrane permeability to sodium.

Animals↗
PubMed1976

Effects of nerve activity on the postsynaptic membrane of skeletal muscle.

The effect of nerve activity on the sensitivity of the neuromuscular junction to acetylcholine was studied. After 1 h of nerve stimulation the flexor hallucis longus muscles of cats become more sensitive to the blocking effect of suxamethonium than before stimulation. Similar results were found using rat soleus muscles. The increased sensitivity to suxamethonium was still observed in muscles from rats which had been curarized during the period of stimulation. Intracellular recordings from end plates of rat soleus muscles revealed an initial transient increase in miniature end-plate potential (MEPP) frequency after stimulation and an increase in the amplitude of MEPPs which persisted for as long as 4 h. Moreover the depolarising responses to acetylcholine and suxamethonium added to the bath were always greater in stimulated muscles. It was therefore concluded that activity of the motor nerve increases the sensitivity of the end plates to transmitter.

Acetylcholine↗
PubMedDate not supplied

Some factors affecting spontaneous transmitter release in dystrophic mice.

Neuromuscular junctions of slow- and fast-twitch skeletal muscles from dystrophic (dy2J/dy2J) and control mice of the C57BL/6J strain were used to investigate the effect of muscular dystrophy on nerve-terminal regulation of their intracellular concentration of free calcium ions. The frequency of spontaneous miniature endplate potentials (MEPPs) was taken as an indicator of the intraterminal free calcium ion concentration. Dicoumarol, 2,4-dinitrophenol, ruthenium red, and the calcium ionophore A-23187 all potentiated the MEPP frequency in dystrophic muscles at concentrations which had negligible effects on normal muscles. Dystrophic muscle preparations were also more sensitive to an increased extracellular calcium concentration. Usually, these manipulations had more effect on the nerve terminals of dystrophic slow muscle than on those of dystrophic fast muscle. We conclude that muscular dystrophy alters the nerve terminal's ability to regulate the concentration of intracellular free calcium ions.

Animals↗