Studies on the osmotic disruption and resealing of synaptosomes

The release of lactate dehydrogenase and K+ when synaptosomes are exposed to resuspension in media of various osmolarity has been investigated in order to measure their disruption. Even when resuspended in distilled water a significant percentage (10-20%) of lactate dehydrogenase and K+ remains unreleased. The particles containing these substances sediment to the same density as synaptosomes. Synaptosomes retaining their internal organelles after hypoosmotic treatment can be seen in electron micrographs. Resealing of disrupted synaptosomes was measured by the inclusion of [14C]sucrose. The resealing is spontaneous, essentially complete (80-90%) within 20 min and not noticeably affected by temperature, pH, or the addition of fusogen. The synaptosome preparation after hypoosmotic disruption will therefore contain some undisrupted synaptosomes with some or all of their complement of cytoplasmic constituents, as well as resealed synaptosomes. The retention of the ability of the hypoosmotically treated preparation to convert [14C]choline to [14C]acetylcholine is demonstrated as an example of the disproportionate effect these undisrupted particles have on its properties.