<Li> Proteins embedded in the vesicle membrane are now part of the plasma membrane . The side of the protein that was facing the inside of the vesicle now faces the outside of the cell . This mechanism is important for the regulation of transmembrane and transporters . </Li> <P> Retrieval of synaptic vesicles occurs by endocytosis . Some synaptic vesicles are recycled without a full fusion into the membrane (kiss - and - run fusion), while others require a complete reformation of synaptic vesicles from the membrane by a specialized complex of proteins (clathrin). Non-constitutive exocytosis and subsequent endocytosis are highly energy expending processes, and thus, are dependent on mitochondria . </P> <P> Examination of cells following secretion using electron microscopy demonstrate increased presence of partially empty vesicles following secretion . This suggested that during the secretory process, only a portion of the vesicular content is able to exit the cell . This could only be possible if the vesicle were to temporarily establish continuity with the cell plasma membrane, expel a portion of its contents, then detach, reseal, and withdraw into the cytosol (endocytose). In this way, the secretory vesicle could be reused for subsequent rounds of exo - endocytosis, until completely empty of its contents . </P>

Exocytosis is carried out by proteins in the cell membrane