Chinese hamster ovary cell lysosomes rapidly exchange contents.

Abstract

We have used cell fusion to address the question of whether macromolecules are rapidly exchanged between lysosomes. Donor cell lysosomes were labeled by the long-term internalization of the fluid-phase pinocytic markers, invertase (sucrase), Lucifer Yellow, FITC-conjugated dextran, or Texas red-conjugated dextran. Recipient cells contained lysosomes swollen by long-term internalization of dilute sucrose or marked by an overnight FITC-dextran uptake. Cells were incubated for 1 or 2 h in marker-free media before cell fusion to clear any marker from an endosomal compartment. Recipient cells were infected with vescicular stomatitis virus as a fusogen. Donor and recipient cells were co-cultured or 1 or 2 h and then fused by a brief exposure to pH 5. In all cases, extensive exchange of content between donor and recipient cell lysosomes was observed at 17.degree.C. Incubation of cell syncytia at 17.degree. C blocked lysosome/lysosome exchange, although a "priming" process(es) appeared to occur at 17.degree.C. The kinetics of lyso-some/lysosome exchange in fusions between cells containing invertase-positive lysosomes and sucrose/positive lysosomes indicated that lysosome/lysosome exchange was as rapid, if not more rapid, than endosome/lysosome exchange. These experiments suggest that in vivo the lysosome is a rapidly intermixing organellar compartment.