Low-voltage gene transfer.

Biotechnologists often employ an electric current to punch a tiny hole into a cell through which they can then insert a foreign gene. The high voltages and currents typical of this procedure, called electroporation, can heat the treated cells, however-often damaging or killing all but 10 to 30 percent of them, notes Robert E. Schmukler of Pore Squared Bioengineering in Rock, lie, Md. By redesigning the environment in which electroporation occurs, he's been able to drop the current to one-thousandth of what had previously been needed. This "kinder and gentler" approach boosts cell survival to at least 93 percent, he reports.

The trick, he found, is to use a thin film of an electrically insulating material perforated with tiny holes around 2 micrometers in diameter. He bathes the film in a solution containing the foreign genes, then spreads the cells to be treated across the top. When he applies a weak vacuum to the underside of the film, suction draws a tiny fingerlike projection from each cell into a different hole. Then Schmukler switches on a roughly 10volt potential between electrodes above and below the film.

Because the film doesn't conduct electricity, the current is drawn through the holes, each now filled with a piece of a cell. The electric field inside the film's narrow holes rises almost 1,000-fold, easily reaching the magnitude necessary to open a pore at the tip of each cell's projection. This breach allows some of the gene-laden solution to enter. Because the current remains low, around 25 milliamperes, little heating occurs.

Schmukler has tested a prototype of his patented system with two different genes and two different types of mammalian cells, in a separate test-tube experiment designed to emulate gene therapy in an animal tissue, he has used this porous-film system to insert genes for a fluorescent enzyme into a living heart vessel. Proof that the technique worked was visible 3 days later, when the new genes caused the vessel's cells to emit a green glow.