At a neuromuscular junction, if all endocytosis were to be blocked (for example,

Question

At a neuromuscular junction, if all endocytosis were to be blocked (for example, by using either -bungarotoxin or dynasore) while all other aspects of neuromuscular transmission remained unaltered at 10 EPP's/sec, assuming a normal rate of endocytosis, what is the maximum sustainable rate of neuromuscular transmission?

(Hint: Look for the rate-limiting step to calculate maximum sustainable rates.)

(Some useful and some not-so-useful numbers: 750,000 SV's per endplate; quantal content (N) of the EPP = 100; sufficient clathrin for 25,000 coated vesicles per endplate at any instant. Exocytosis requires 0.1 msec. Assume the period of endocytosis and clathrin detachment requires 30 seconds, and that filling of SV's with ACh must occur prior to clathrin detachment from the coated vesicle.) (Note: This question does not involve -BuTx; it involves -BuTx.)

Explanation / Answer

macimum sustainable rate= number per endplate X quantal content/ number of vesicles x unaltered rate x 0.1

=>750000x100/25000x10 x0.1=>3000 seconds=3000/60=>50 minutes

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