Protein microinjection by protease permeabilization of fibroblasts

Exposure of cultured diploid fibroblasts to protease solutions induces a hyperpermeable state which permits entry of exogenous macromolecules directly into the cytosol. We have exploited this finding to devise a microinjection method whose chief advantages are simplicity and good retention of cell viability. Proteins successfully injected by this technique range from insulin to thyroglobulin. The amounts injected range from 4 X 10(5) to 5 X 10(6) molecules/cell.