Coated vesicle morphology and sub-populations at the neuromuscular junction

Serial sections of frog cutaneous pectoris neuromuscular junctions were examined to determine if isolated coated vesicles in one section are connected to infoldings of the presynaptic membrane in adjacent sections or are truly pinched off from the plasmalemma. Twenty percent of the coated vesicles examined serially were isolated from plasmalemma. In addition, two populations of coated vesicles were observed: those the size of synaptic vesicles and a smaller population (8% of total) of larger diameter (100 nm).