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The origin of the muscle fasciculation caused by funnel-web spider venom
Abstract:
The origin of the fasciculation of skeletal muscle produced by funnel-web spider venom (FSV) has been examined in mouse phrenic nerve hemi-diaphragm preparations, FSV from male spiders at concentrations greater than 10(-6) g/ ml invariably produced muscle fasciculation which could be prevented by d-tubocurarine (14micron), tetrodotoxin (0.3 micron) or by increasing the external magnesium concentration or calcium concentration. Diphenyl hydantoin (3-6 X 10(-5) M) was able to reduce these fasciculations in some experiments. In curarized preparations, multiple end plate potentials (EPPs) in response to single stimuli and bursts of spontaneous EPPs were seen in the presence of FSV (10(-5) g/ml). Extracellular recordings from phrenic nerves in the presence of FSV (10(-5) g/ml) revealed additional components in compound action potentials elicited by single stimuli, and "spontaneous" electrical activity was observed in unstimulated nerves. This spontaneous activity was abolished by raising the divalent cation concentration in the bathing solution. These results suggest that a primary site of action of FSV is the surface membrane of nerve fibres and that muscle fasciculation arises as a consequence of spontaneous action potentials produced by the venom in motor nerves.
Insights
Funnel-web spider venom (FSV) causes skeletal muscle fasciculation by inducing spontaneous action potentials in motor nerves. This effect, primarily acting on nerve fiber membranes, can be blocked by specific agents and altered by ion concentrations.
Area of Science:
- Neuroscience
- Toxicology
- Pharmacology
Background:
- Funnel-web spider venom (FSV) is known to cause significant physiological effects.
- The precise mechanism underlying FSV-induced muscle fasciculations requires detailed investigation.
Purpose of the Study:
- To elucidate the origin of skeletal muscle fasciculations induced by funnel-web spider venom (FSV).
- To identify the primary site of action of FSV in neuromuscular preparations.
Main Methods:
- Experiments utilized mouse phrenic nerve hemi-diaphragm preparations.
- Electrophysiological recordings (end plate potentials, compound action potentials) and pharmacological interventions were employed.
- Effects of FSV were assessed in the presence and absence of various blocking agents and altered ion concentrations.
Main Results:
- FSV consistently produced muscle fasciculations at concentrations above 10(-6) g/ml.
- Fasciculations were preventable by d-tubocurarine, tetrodotoxin, and increased magnesium or calcium concentrations.
- FSV induced multiple end plate potentials and spontaneous bursts of EPPs in curarized preparations.
- Extracellular recordings showed additional components in nerve action potentials and spontaneous nerve activity, abolished by increased divalent cations.
Conclusions:
- FSV primarily acts on the surface membrane of nerve fibers.
- Muscle fasciculations result from spontaneous action potentials generated by FSV in motor nerves.
- The venom's neurotoxic effects are modulated by extracellular ion concentrations.