A 34-year-old woman suffering from hemifacial spasms started a treatment with botulin toxin injected directly into the abnormally contracting muscles. Which of the following molecular actions most likely mediated the therapeutic effect of the drug in the patient’s disorder?
A. Long lasting activation of Nm receptors B. Inhibition of acetylcholine storage into synaptic vesicles C. Inhibition of choline acetyltransferase D. Inhibition of acetylcholine exocytosis from cholinergic terminals E. Stimulation of acetylcholinesterase F. Opening of CA++ channels in cholinergic terminals
Inhibition of acetylcholine exocytosis from cholinergic terminals-learning objective: explain the mechanism of action of botulin toxinanswer: dbotulin toxin must get inside the axon terminals in order to cause paralysis. following theattachment of the toxin to proteins on the surface of axon terminals, the toxin can be taken intoneurons by endocytosis. there it is able to cleave endocytotic vesicles and reach the cytoplasm.the light chain of the toxin has protease activity and proteolytically degrades a specific proteinthat is required for vesicle fusion that releases acetylcholine from the axon endings. in this wayit prevents neurosecretory vesicles from fusing with the nerve synapse plasma membrane andreleasing the neurotransmitter.a, b, c, e, f) (see explanation above)