MOUSE MOTOR-NERVE TERMINAL IMMUNOREACTIVITY TO SYNAPTOTAGMIN-II DURING SUSTAINED QUANTAL TRANSMITTER RELEASE

An antibody directed against the lumenal NH2-terminus of synaptotagmin II was used to examine the distribution of this vesicular protein eit her after spontaneous acetylcholine release or after sustained release induced by La3+ or alpha-latrotoxin, in conditions that prevent endoc ytosis. The detection of the epitope was examined in the presence or a bsence of Triton X-100. We show that, in resting conditions of transmi tter release, permeabilization of nerve terminal membranes is required for obvious detection of synaptotagmin II immunoreactivity whereas du ring sustained rates of quantal release, permeabilization is not neces sary. These data indicate that, in the latter conditions, synaptotagmi n II is incorporated into the terminal axolemma and its intravesicular domain exposed at the extracellular nerve terminal surface.