Characterization of a vertebrate neuromuscular junction that demonstrates selective resistance to botulinum toxin.
(1/266)
Botulinum toxin blocks transmitter release by proceeding through a series of four steps: binding to cell surface receptors, penetration of the cell membrane by receptor-mediated endocytosis, penetration of the endosome membrane by pH-induced translocation, and intracellular proteolysis of substrates that govern exocytosis. Each of these steps is essential for toxin action on intact cells. Therefore, alterations in cell structure or cell function that impede any of these steps should confer resistance to toxin. In the present study, screening for susceptibility to four serotypes of botulinum toxin revealed that the cutaneous-pectoris nerve-muscle preparation of Rana pipiens is resistant to type B botulinum toxin. Resistance was demonstrated both by electrophysiologic techniques and by dye-staining techniques. In addition, resistance to serotype B was demonstrated at toxin concentrations that were 2 orders of magnitude higher than those associated with blockade produced by other serotypes. In experiments on broken cell preparations, type B toxin cleaved synaptobrevin from frog brain synaptosomes. However, the toxin did not bind to frog nerve membranes. These findings suggest that resistance is due to an absence of cell surface receptors for botulinum toxin type B. The fact that cutaneous-pectoris preparations were sensitive to other botulinum toxin serotypes (A, C, and D), as well as other neuromuscular blocking agents (alpha-latrotoxin, beta-bungarotoxin), indicates that botulinum toxin type B receptors are distinct. (+info)
Omitting antagonism of neuromuscular block: effect on postoperative nausea and vomiting and risk of residual paralysis. A systematic review.
(2/266)
We have estimated the effect of omitting antagonism of neuromuscular block on postoperative nausea and vomiting. A systematic search (MEDLINE, EMBASE, Biological Abstracts, Cochrane library, reference lists and hand searching; no language restriction, up to March 1998) was performed for relevant randomized controlled trials. In eight studies (1134 patients), antagonism with neostigmine or edrophonium was compared with spontaneous recovery after general anesthesia with pancuronium, vecuronium, mivacurium or tubocurarine. On combining neostigmine data, there was no evidence of an antiemetic effect when it was omitted. However, the highest incidence of emesis with neostigmine 1.5 mg was lower than the lowest incidence of emesis with 2.5 mg. Numbers-needed-to-treat to prevent emesis by omitting neostigmine compared with using it were consistently negative with 1.5 mg, and consistently positive (3-6) with 2.5 mg. There was a lack of evidence for edrophonium. In two studies, three patients with spontaneous recovery after mivacurium or vecuronium needed rescue anticholinesterase drugs because of clinically relevant muscle weakness (number-needed-to-harm, 30). Omitting neostigmine may have a clinically relevant antiemetic effect when high doses are used. Omitting antagonism, however, introduces a non-negligent risk of residual paralysis even with short-acting neuromuscular blocking agents. (+info)
Rapid and reversible effects of activity on acetylcholine receptor density at the neuromuscular junction in vivo.
(3/266)
Quantitative fluorescence imaging was used to study the regulation of acetylcholine receptor (AChR) number and density at neuromuscular junctions in living adult mice. At fully functional synapses, AChRs have a half-life of about 14 days. However, 2 hours after neurotransmission was blocked, the half-life of the AChRs was now less than a day; the rate was 25 times faster than before. Most of the lost receptors were not quickly replaced. Direct muscle stimulation or restoration of synaptic transmission inhibited this process. AChRs that were removed from nonfunctional synapses resided for hours in the perijunctional membrane before being locally internalized. Dispersed AChRs could also reaggregate at the junction once neurotransmission was restored. The rapid and reversible alterations in AChR density at the neuromuscular junction in vivo parallel changes thought to occur in the central nervous system at synapses undergoing potentiation and depression. (+info)
Anaesthesia for strabismus surgery: a regional survey.
(4/266)
An increase in the demand by local surgeons for neuromuscular block during strabismus surgery, and the forced duction test in particular, led us to review the literature and conduct a regional survey of anaesthetic techniques used. A questionnaire was distributed to 379 anaesthetists in the region and 264 responses were received. The results demonstrated that 55% of paediatric patients and 66% of adult patients may have been operated on under suboptimal conditions; residual tone may have been present in the extraocular muscles during forced duction testing and strabismus correction. (+info)
Failure to prevent an anaphylactic reaction to a second neuromuscular blocking drug during anaesthesia.
(5/266)
Skin testing is used widely to determine the drug responsible for an anaphylactic reaction during anaesthesia. When a neuromuscular blocking drug in incriminated as the cause of a reaction, it is usual for neuromuscular blocking drugs which do not produce positive skin tests to be considered safe for subsequent use during anaesthesia. We describe three patients in whom false negative skin tests led to a second severe anaphylactic reaction to another neuromuscular blocking drug. (+info)
Comparison of the intubation conditions provided by rapacuronium (ORG 9487) or succinylcholine in humans during anesthesia with fentanyl and propofol.
(6/266)
BACKGROUND: Currently, the only approved muscle relaxant with a rapid onset and short duration of action is succinylcholine, a drug with some undesirable effects. Rapacuronium is an investigational nondepolarizing relaxant that also has a rapid onset and short duration and consequently should be compared with succinylcholine in its ability to facilitate rapid tracheal intubation. METHODS: This prospective, randomized clinical trial involved 336 patients. Anesthesia was induced with fentanyl and propofol and either 1.5 mg/kg rapacuronium or 1.0 mg/kg succinylcholine. The goal was to accomplish tracheal intubation by 60 s after administration of the neuromuscular blocking drug. Endotracheal intubation was performed, and conditions were graded by a blinded investigator. Recovery of neuromuscular function was assessed by electromyography. RESULTS: Intubation conditions were evaluated in 236 patients. Intubation by 60 s after drug administration occurred in 100% of patients with rapacuronium and in 98% with succinylcholine. Intubation conditions were excellent or good in 87% of patients with rapacuronium and in 95% with succinylcholine (P < 0.05). The time (median and range) to the first recovery of the train-of-four response was 8.0 (2.8-20.0) min with rapacuronium and 5.7 (1.8-17.7) min with succinylcholine (P < 0.05). The overall incidence of adverse effects was similar with both drugs. CONCLUSIONS: A 1.5-mg/kg dose of rapacuronium effectively facilitates rapid tracheal intubation. It can be considered a valid alternative to 1.0 mg/kg succinylcholine for this purpose. (+info)
Rapid vasodilation in response to a brief tetanic muscle contraction.
(7/266)
To test the hypothesis that vasodilation occurs because of the release of a vasoactive substance after a brief muscle contraction and to determine whether acetylcholine spillover from the motor nerve is involved in contraction-induced hyperemia, tetanic muscle contractions were produced by sciatic nerve stimulation in anesthetized dogs (n = 16), instrumented with flow probes on both external iliac arteries. A 1-s stimulation of the sciatic nerve at 1. 5, 3, and 10 times motor threshold increased blood flow above baseline (P < 0.01) for 20, 25, and 30 s, respectively. Blood flow was significantly greater 1 s after the contraction ended for 3 and 10 x motor threshold (P < 0.01) and did not peak until 6-7 s after the contraction. The elevations in blood flow to a 1-s stimulation of the sciatic nerve and a 30-s train of stimulations were abolished by neuromuscular blockade (vecuronium). The delayed peak blood flow response and the prolonged hyperemia suggest that a vasoactive substance is rapidly released from the contracting skeletal muscle and can affect blood flow with removal of the mechanical constraint imposed by the contraction. In addition, acetylcholine spillover from the motor nerve is not responsible for the increase in blood flow in response to muscle contraction. (+info)
Effects of non-depolarizing neuromuscular blocking agents on norepinephrine release from human atrial tissue obtained during cardiac surgery.
(8/266)
We have studied the effect of non-depolarizing neuromuscular blocking agents, at concentrations present in serum during anaesthesia, on release of [3H]-norepinephrine ([3H]NE) from superfused atrial appendage obtained during cardiac surgery from 48 patients. Three of the neuromuscular blocking agents (pancuronium, gallamine and rocuronium), which are known to cause an increase in heart rate during anaesthesia, increased stimulation-evoked release of [3H]NE. In contrast, (+)tubocurarine and pipecuronium, neuromuscular blocking agents that do not cause tachycardia, did not affect release of NE. Org 9487 significantly enhanced release while SZ1677 was ineffective, even at concentrations higher than those expected after administration of a 2 x ED95 dose. Atropine enhanced release. These data suggest that the axon terminals of sympathetic nerves in human heart have muscarinic heteroreceptors whose activation by acetylcholine (ACh) released from the vagal nerve reduces release of NE. This action contributes to lowering of heart rate. Therefore, any neuromuscular blocking agent with antimuscarinic actions and capable of increasing the release of NE may produce tachycardia. (+info)