Education in cancer prevention for GPs.
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Family Practice↗
Biomedical subjects
W Betz
Publications and source records attributed to W Betz.
Effects of innervation on acetylcholine sensitivity of developing muscle in vitro.
1. Chick embryo skeletal muscle fibres were grown in culture. The acetylcholine (AACh) sensitivity of non-innervated fibres was compared with that of fibres innervated in vitro by chick embryo ciliary ganglion neurones. 2. The general pattern of ACh sensitivity was unchanged by innervation: ACh hot spots were superimposed on a background of uniform ACh sensitivity. 3. Quantitative comparisons revealed two differences between non-innervated and innervated fibres. First, hot spots were encountered about one third more often on innervated fibres. Secondly, about one-third of the hot spots on innervated fibres had significantly higher ACh sensitivities than the remainder, which were similar to those on control fibres. 4. Apossible explanation of these results is that nerves which form synapses induce the appearanceof end-plates which have higher ACh sensitivities than the pre-existing ACh hot spots.
Acetylcholine↗
Properties of isolated adult rat muscle fibres maintained in tissue culture.
1. Adult rat skeletal muscles were dissociated by collagenase treatment and trituration, and the isolated muscle fibres were maintained in vitro for 2-3 weeks. At various stages, the fibres were examined physiologically and morphologically. 2. The isolated fibres underwent some changes characteristic of muscle denervated in vivo. For instance, input resistance increased and extrajunctional acetylcholine (ACh) receptors appeared. In addition, the beginning stages of apparent muscle fibre fragmentation were observed. 3. In other respects, the cultured isolated fibres behaved differently than in vivo denervated fibres. Fibrillation developed only occasionally in vitro. The onset of ACh supersensitivity was slower (6 days) than after denervation in vivo (2-3 days). Some fibres developed localized regions of destriation, which apparently was due to loss of in-register alignment of myofibrils.
Acetylcholine↗
The formation of synapses between chick embryo skeletal muscle and ciliary ganglia grown in vitro.
1. Chick embryo ciliary ganglia (explanted) and skeletal muscle (dissociated) were grown together in vitro for up to 3 weeks. Nerve processes sprouted from the ganglia and contacted neighbouring myotubes and striated muscle fibres. 2. Spontaneous action potentials and subthreshold e.p.p.s. were recorded from muscle fibres with intracellular micropipettes. Similar potentials could be evoked by electrical stimulation of the ganglion. The pharmacological effects of curare and tetrodotoxin were identical to those observed at adult vertebrate neuromuscular junctions. 3. The amplitude, but not the frequency, of the spontaneous potentials was affected by changing the muscle fibre membrane potential. The reversal potential of evoked synaptic potentials occurred at a membrane potential of about 0 mV.
Action Potentials↗
Functional and non-functional contacts between ciliary neurones and muscle grown in vitro.
1. In cultures of chick embryo skeletal muscle and ciliary ganglia, muscle fibres near a ganglion were contacted by many individual nerve processes. Experiments were performed to determine if these muscle fibres were multiply innervated, and if any of the nerve-muscle contacts were non-synaptic. 2. Synaptic potentials evoked by electrical stimulation of a ganglion were graded with stimulus strength. When two ganglia were plated near each other, synaptic potentials could be evoked in some muscle fibres by stimulation of either ganglion. These observations suggest that muscle fibres were multiply innervated. 3. Spontaneous synaptic potentials recorded from single muscle fibres with two widely spaced micropipettes varied in a manner which suggested that the synapses were distributed at different points on the surface of the muscle fibres. 4. Stimulation of some nerve processes failed to evoke synaptic potentials in muscle fibres contacted by those processes. Such nerve-muscle contacts were not strongly adhesive, and the nerves were peeled easily from the surface of the muscle with a micropipette. On the other hand, nerve processes which formed synaptic contacts with muscle fibres seemed to be tightly adherent to the muscle. 5. Electron microscopic observations of nerve-muscle contacts revealed that the vast majority of such contacts lacked morphological specializations characteristic of mature neuromuscular synapses.
Animals↗
Effects of proteolytic enzymes on function and structure of frog neuromuscular junctions.
1. Frog cutaneous pectoris nerve-muscle preparations were incubated with collagenase and protease and examined with electrophysiological and electron microscopic techniques.2. The physiological properties and intracellular ultrastructural appearance of individual muscle and nerve cells were not affected by the enzyme treatment. However, neuromuscular transmission and the morphology of the nerve-muscle junction were altered.3. Collagenase produced an irreversible loss of activity of end-plate cholinesterase and a partial loss of stainable ;synaptic cleft material'.4. Protease produced these changes and, in addition, the entire basement membrane was digested, which led to ;synaptic disjunction' of nerve terminals and muscle end-plates.
Acetylcholinesterase↗
"Disjunction" of frog neuromuscular synapses by treatment with proteolytic enzymes.
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Acetylcholine↗
Does curare affect transmitter release?
1. The effect of curare on the amount of transmitter released by a nerve stimulus was studied in frog and rat nerve-muscle preparations using electrophysiological techniques.2. When the frog sartorius nerve-muscle preparation was exposed to low doses of curare, the amplitudes of spontaneous miniature end-plate potentials and end-plate currents (e.p.c.s, measured under ;voltage clamp' conditions) were reduced to the same extent, suggesting that the drug did not alter the number of transmitter quanta released by nerve stimulation.3. With higher doses of curare in frog muscle treated with glycerol to abolish twitching, quantum content was estimated from the coefficient of variation (CV) of e.p.c.s. The measured CV increased slightly in curare; this increase probably resulted from a relatively greater contribution of random noise to the observed fluctuations when the e.p.c. was reduced by curare.4. In the rat diaphragm, muscle fibres were cut to block twitching. This procedure produced, among other changes, a reduction in the muscle fibre space constant, so that junctional signals were distorted by the cable properties of the muscle fibre when, as often occurred, micro-electrodes were more than 100-200 mu from the end-plate focus. This produced errors in estimates of quantum content; when these errors were accounted for, it appeared that curare did not significantly alter quantum content.5. It is concluded that if curare affects transmitter release at all, its effect must be much smaller than its well known post-synaptic blocking action.
Animals↗