BioWorld International Correspondent

NORWICH, UK - A team from Imperial College London and Cambridge University have devised a method for imaging cells without killing them, making it possible to watch biology in action. Among the processes recorded in real time are the congregating of protein complexes, microvilli responding to changes in osmotic pressure and viruses preparing to infect a cell.

The researchers have used their equipment to deliver single molecules to precise locations on the surface of cells. They have "painted" nanoscale pictures by the molecule-by-molecule application of fluorescent DNA and simulated a heart attack in a petri dish by administering a single molecule of a toxin to a cardiomyocyte, prompting it to become arrhythmic.

"The big advantage of our technique is that it is non-contact," said David Klenerman, of Cambridge University, speaking at the BA Festival of Science here last week. "A lot of structural biology is based on examining dead cells. Now we can see live cells. It is not the highest resolution that has been achieved, but it is the highest achieved on a live cell."

The technique, called Scanning Ion Conductance Microscopy (SICM) uses a micropipette to deliver a small voltage to the surface of the cell. By scanning the pipette across the cell, it is possible to create an image of the surface. No special preparation is required, and the cells can be imaged on standard culture dishes.

In addition, the pipette can be used to perform nanoscale measurements on the cell surface, such as recording a single ion channel or for the controlled addition of reagents.

While SICM is not a new technique, the researchers have produced a micropipette that is smaller than any of its predecessors, enabling the resolution to go down to 10 nanometers.

Using fluorescent DNA, Klenerman and colleagues have painted the Cambridge University crest on a cell in lines that are under one micron in width. "This demonstrates very high control of where you put molecules and shows you can use the technique to do assays on individual living cells," Klenerman said.

The team has studied epithelial kidney cells, uncovering the same features that are seen in scanning electron micrographs, but then going on to follow the life history of microvilli, showing them responding to changes in osmotic pressure. Currently, the researchers are applying the technique to visualize ion channels in neurons, and Klenerman said this is leading to the development of a smart patch clamp technique, where the characteristic on/off behavior of ion channels can be followed live.

The micropipettes can be used also to apply pressure to a cell, pushing it down or sucking it up, without actually making contact. That means that it is possible to probe the mechanical properties of individual cells.

Micropipettes can be constructed with a double barrel, to deliver two different molecules at the same time, and it also is possible to construct them with four and eight barrels.

The technique opens up the possibility of performing cell repairs, but Klenerman said that is some way off.

"We can locally deliver reagents, but at present we are getting information about normal cells and finding out about diseased cells. You could then think about using that information to repair damaged cells."

Imperial College has spun out a company, Ionscope Ltd., to sell the equipment. Klenerman told BioWorld International this was suitable for research purposes only at present. "It is far from an established technology. There is some way to go before it could be applied systematically, but we have shown what is possible."