Chinese hamster ovary cell lysosomes rapidly exchange contents.

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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.