I'm reading the following paper:


The part I am really confused about is when they say:

Exocytosis appears to use two alternative pathways: clathrin-mediated endocytosis (CME), which is well established by numerous lines of evidence, and the more controversial ‘kiss-and-run’ pathway, which involves direct retrieval of a vesicle at the site of fusion

My question is .. How can exocytosis (contents inside of cell are transported to outside of cell) use clathrin mediated endocytosis?

I thought endocytosis is the opposite of exocytosis, so why do synaptic vesicles use clathrin mediated endocytosis as a method of exocytosis?


That sentence is located in a paragraph titled "Stages 5-7: Endocytosis and recycling": it's talking about recycling exocytosed membrane which is necessary for making vesicles for further exocytosis.

The sentences before the part you quoted are:

Synapses possess highly efficient mechanisms for retrieving SVs from the plasma membrane of the presynaptic terminal after exocytosis. Fast regeneration of functional SVs is a prerequisite for synapses to function during prolonged activity.

I think the passage is just somewhat confusingly worded, in that "exocytosis" is used as the subject of the sentence which is strange in this context. You could rewrite that sentence:

There appear to be two alternative pathways to recycle membrane for exocytosis: clathrin-mediated...

The author likely intended the word "exocytosis" in the original sentence to mean "the entire process of releasing synaptic vesicles, including formation of those vesicles" rather than the specific event of vesicle fusion with the membrane. Kind of like if I referred to "planting trees" as part of "logging" - you typically think of "logging" as cutting down trees, but in the right context it can make sense to refer to the process: you need to have a tree there to be able to cut it down. I could say "Trees are necessary for logging. Logging uses two alternative pathways: planting trees directly as saplings, or leaving land to grow new forest naturally over a number of years."


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