Automatic positioning of a microinjector in mouse ES cells and rice protoplasts.

A 2-channel (2C) microinjector was prepared by pulling a glass capillary with a theta-shaped cross section. One channel was used as a potential measuring electrode (MeaE) and the other was used as an electrophoretic introduction electrode (IntE). The 2C microinjector was propelled by an oil pressure manipulator driven by a pulse motor, while the MeaE output was recorded continuously. When the 2C microinjector penetrated the cell membrane of a mouse ES cell or a rice protoplast, the output potential changed sharply. The differential of this potential change was used as a stop signal for the pulse motor. Thus, the microinjector was correctly positioned in the cell without losing cell viability. Its success rate was 73% and 84% for ES cells and rice protoplasts, respectively. After the positioning of the microinjector in the cell, Lucifer yellow (LY) was introduced via IntE. Under these conditions, the rate of viable cells was 16% and 62% for ES cells and rice protoplasts, respectively.