A quantitative study of ultramicroinjection of macromolecules into animal cells

Improvements in the technique of ultramicroinjection of macromolecules into animal cells are described. The method is based on the Sendai virus-induced fusion of animal cells with erythrocyte ghosts containing trapped macromolecules. Fusion of hepatoma tissue culture (HTC) cells with ghosts prepared by hemolysis of erythrocytes in the presence of cytochrome C is much more efficient than fusion with ghosts prepared in the presence of bovine serum albumin (BSA) as in previous investigations. La⁺⁺⁺ is more efficient in promoting fusion and less toxic to cells than Mn⁺⁺, which was used previously. Thus in all subsequent experiments, erythrocytes were hemolyzed in the presence of cytochrome C plus other macromolecules to be trapped, and the resultant ghosts fused in the presence of La⁺⁺⁺. The percentage of HTC cells which fused with ghosts reached 80% in many experiments. Ghosts containing ¹²⁵I-BSA were used to measure the number of BSA molecules injected into HTC cells. About 10⁶ BSA molecules were injected per fused cell. The overall efficiency of injection was low (about 0.02% of the starting material).