Synaptic Vesicles Isolated from the Electric Organ of Torpedo Californica Posses Multiple Classes of Neurotransmitter Transporters

Abstract

The fusion of synaptic vesicles with the presynaptic membrane, and the subsequent release of small chemical neurotransmitters is the fundamental process by which neurons communicate at chemical synapses, and it has long been proposed that most neurons release a single type of small molecule neurotransmitter. The simplicity of one neuron, one neurotransmitter has come under intense scrutiny as examples of neurons that appear to co-release two or more neurotransmitters at single synapses (neurotransmitter synergy) have been identified. One such synapse is that of the electric organ of Torpedo californica; synaptic vesicles isolated from this single class of neurons appear to contain the neurotransmitter acetylcholine as well as the neurotransmitter ATP. We used immunofluorescence labeling in conjunction with single-molecule TIRF microscopy to observe whether one or more neurotransmitter transporters could be detected on single synaptic vesicles. We found that the vesicular acetylcholine transporter (VAChT) and several solute carrier proteins (SLC17A) co-localized to the same vesicles. The presence of multiple types of neurotransmitter transporters - and potentially neurotransmitters - in individual synaptic vesicles raises fundamental questions about chemical synaptic transmission at the electric organ of T. Californica. In addition, this approach can be applied to other synapses in order to address the prevalence of neurotransmitter synergy and co-release at chemical synapses.