Two sites of intracellular localization of rhodaminyl-phalloidin in hepatocytes.

The uptake of a fluorescent phallotoxin (tetramethylrhodaminyl-phalloidin) into rat hepatocytes has been studied. The experiments were performed in vitro, using freshly isolated hepatocyte suspensions or monolayers of hepatocytes cultured for up to 5 days, as well as in vivo, by investigating cryostat sections of a liver from an animal injected with the labelled toxin. In vitro, in freshly isolated hepatocytes, a staining of actin was observed. On the contrary, if the hepatocytes were cultured, only fluorescent endocytotic vesicles were found accumulated around the nucleus, and remaining in the cells unchanged for several days. In vivo, both fluorescent patterns were observed, often in one and the same cell. The endocytotic vesicles of rhodaminylphalloidin looked very similar to those obtained with fluoresceinyl-concanavalin A. navalin A. We conclude that in all systems the fluorescent phallotoxin enters the hepatocytes by endocytosis. However, in the freshly isolated cells the endocytotic vesicles apparently undergo some kind of processing with release of the toxin and subsequent staining of cellular actin, while in cultured hepatocytes the endocytotic vesicles persist unprocessed.