An ultrastructural and chemical analysis of the effect of triton X-100 on synaptic plasma membranes

Triton X-100 treatment of synaptic plasma membrane fractions selectively dissociates membrane constituents. At an ultrastructural level the synaptic complex resists Triton treatment when Ca²⁺ is present so that the synaptic complex is dissociated from the bulk of the adjoining plasma membrane. The synaptic complex retains its selective affinity for phosphotungstic acid and can therefore be unambiguously identified in the Triton-insoluble residue. At a chemical level Triton results in differential solubilization of membrane protein, phospholipid and sialic acid. Under conditions favorable for preserving synaptic complex, the insoluble residue retains about 60 % of its initial protein, 70 % of its initial phospholipid phosphorus, and 80 % of its initial sialic acid. Over 75 % of the acetylcholinesterase is solubilized, but essentially all of the 5′-nucleotidase and alkaline phosphatase of the synaptic plasma membrane fraction remains insoluble. The implications of these data for synaptic function and the structuring of synaptic plasma membranes are discussed.