Autophagic sequestration of [14C]sucrose, introduced into rat hepatocytes by reversible electro-permeabilization

Isolated rat hepatocytes could be made permeable to small molecules such as [14C]sucrose (but not to proteins) by subjecting the cells to repeated electric discharges in a high-voltage field. During subsequent incubation at 37 degrees C, the permeability changes were reversed within 15 min, the electro-injected [14C]sucrose remaining trapped inside the re-sealed plasma membrane. Autophagic sequestration of [14C]sucrose, i.e., the transfer of radioactivity from cytosol to sedimentable vesicles (autophagosomes and lysosomes), could be followed by incubating the [14C]sucrose-loaded hepatocytes for up to 2 h at 37 degrees C. After incubation, the cells were disrupted by a single high-voltage discharge in electrolyte-free medium (sucrose), and sedimentable cell components were separated from the cytosol by centrifugation through metrizamide. By the use of these methods, which are particularly suitable for the analysis of many small cell samples, it could be shown that [14C]sucrose was autophagically sequestered in the hepatocytes at a rate of 4-5%/h. The sequestration was nearly completely inhibited by the specific autophagy inhibitor 3-methyladenine.