Plasma Membrane of Torpedo Synaptosomes: Morphological Changes During Acetylcholine Release and Evidence for a Specific Protein

Publisher Summary Torpedo electric organs have an abundant and purely cholinergic innervations and are therefore very convenient for biochemical studies of neurotransmission at peripheral synapses. As is the case for brain, nerve terminals pinched off during tissue subfractionation can be isolated as sealed particles = synaptosomes. The main advantage of Torpedo synaptosomal fractions is that all the synaptosomes are cholinergic. This permits the study of their physiological properties without interference from noncholinergic materials. The large field electron micrograph illustrates the homogeneity and purity of the synaptosomal fraction. Freeze-fracture methods have been used to follow morphological modifications accompanying neurotransmitter release, because a large surface of the presynaptic membrane can be analyzed. Ultrarapid freezing procedures permit the avoidance of any chemical fixation and are, therefore, very suitable to catch transient membrane modifications. The study of acetylcholine (Ach) release suffers from the impossibility of controlling the intracellular composition of synaptosomes.