The involvement of synaptophysin, a synaptic vesicle-specific protein, in transmitter release at neuromuscular synapses was studied by intracellular application of synaptophysin antibodies into presynaptic neurons. Polyclonal antibodies or their Fab fragments were loaded into spinal neurons by injection into one of the early blastomeres of Xenopus embryos 1 day prior to culturing or, alternatively, directly through a whole-cell recording pipette at the soma of cultured neurons. At synapses made by antibody-loaded neurons in culture, the spontaneous synaptic currents showed marked reduction in frequency without significant change in their mean amplitude. The impulse-evoked synaptic currents showed reduced amplitude and increased failure rate. These results suggest that interference with synaptophysin function by antibody binding inhibits transmitter secretion.
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