MDMA, also known as ecstasy, is a small molecule that can be transported into a secretory vesicle, bind a proton in there, and diffuse out of the vesicle. By carrying protons out of the secretory vesicle, MDMA depletes the proton gradient across the vesicle\\\'s membrane. MDMA directly interferes with ___________ (endocytosis, antiport, exocytosis, or osmosis)