The Journal of Neurophysiology Vol. 82 No. 1 July 1999, pp. 50-59
Copyright ©1999 by the American Physiological Society

Antibodies Against Cysteine String Proteins Inhibit Evoked Neurotransmitter Release at Xenopus Neuromuscular Junctions

 ¹Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260; and  ²Department of Molecular and Medical Pharmacology, UCLA School of Medicine, Los Angeles, California 90095

Poage, Robert E., Stephen D. Meriney, Cameron B. Gundersen, and Joy A. Umbach. Antibodies Against Cysteine String Proteins Inhibit Evoked Neurotransmitter Release at Xenopus Neuromuscular Junctions. J. Neurophysiol. 82: 50-59, 1999.Cysteine string proteins (CSPs) are evolutionarily conserved proteins that are associated with synaptic vesicles and other regulated secretory organelles. To investigate the role of CSPs in vertebrate neuromuscular transmission, we introduced anti-CSP antibodies into the cell bodies of Xenopus spinal motor neurons that form synapses with embryonic muscle cells in culture. These antibodies produced a rapid (within 3-6 min), and in most cases complete, inhibition of stimulus-dependent neurotransmitter secretion. However, spontaneous neurotransmitter release was stable (both in frequency and amplitude) throughout the period of antibody exposure. Several control experiments validated the specificity of the anti-CSP antibody effects. First, the anti-CSP antibody actions were not mimicked either by antibodies against another synaptic vesicle protein SV₂, or by nonspecific immunoglobins. Second, heat treatment of the anti-CSP antibodies eliminated their effect on evoked secretion. Third, immunoblot experiments showed that the anti-CSP and anti-SV₂ antibodies were highly selective for their respective antigens in these Xenopus cultures. We conclude from these results that CSPs are vital constituents of the pathway for regulated neurotransmitter release in vertebrates. Moreover, the selective inhibition of evoked, but not spontaneous transmitter release by anti-CSP antibodies indicates that there is a fundamental difference in the machinery that mediates these secretory processes.