The use of antibody and complement to gain access to the interior of presynaptic nerve terminals.

Treatment of synaptosomes with sera containing antibodies (Ab) directed against synaptosomal membranes and complement (C) alters the plasma membrane so that it becomes selectively permeable to small molecules and ions but not to proteins. When synaptosomes are incubated with Ab and C, a rapid release of intracellular K occurs. This release does not occur after treatment with antiserum alone, or with normal serum + C. Ab + C treatment releases approximately the same amount of K as does detergent treatment or hypotonic lysis, two procedures that extensively disrupt the plasma membrane. The selectivity of the complement-induced lesion is consistent with the equivalent pore radius determined in other systems (Michaels and Mayer 1978; Sears et al. 1964). The lesions are large enough to allow the rapid permeation of small ions, but too small to permit the escape of the soluble cytoplasmic enzyme, lactate dehydrogenase. In addition, electron microscopic studies indicate that Ab + C treatment does not lead to gross morphological disruption of the synaptosomes. Ab + C treated synaptosomes are also permeable to calcium and ATP, as demonstrated by the stimulation of Ca sequestration into endoplasmic reticulum when 45Ca and ATP are added to the incubation medium.