Voltage-dependent interaction between the muscarinic ACh receptor and proteins of the exocytic machinery.

1 Release of neurotransmitter into the synaptic cleft is the last step in the chain of molecular events following the arrival of an action potential at the nerve terminal. The neurotransmitter exerts negative feedback on its own release. This inhibition would be most effective if exerted on the first step in this chain of events, i.e. a step that is mediated by membrane depolarization. Indeed, in numerous studies feedback inhibition was found to be voltage dependent. 2 The purpose of this study is to investigate whether the mechanism underlying feedback inhibition of transmitter release resides in interaction between the presynaptic autoreceptors and the exocytic apparatus, specifically the soluble NSF-attachment protein receptor (SNARE) complex. 3 Using rat synaptosomes we show that the muscarinic ACh autoreceptor (mAChR) is an integral component of the exocytic machinery. It interacts with syntaxin, synaptosomal-associated protein of 25 kDa (SNAP-25), vesicle-associated membrane protein (VAMP) and synaptotagmin as shown using both cross-linking and immunoprecipitation. 4 The interaction between mAChRs and both syntaxin and SNAP-25 is modulated by depolarization levels; binding is maximal at resting potential and disassembly occurs at higher depolarization. 5 This voltage-dependent interaction of mAChRs with the secretory core complex appears suitable for controlling the rapid, synchronous neurotransmitter release at nerve terminals.