Quantum Measurement Could Reveal Ion Flow Through Cell Membranes

Ion channels play a crucial role in the workings of all living cells. The channels are proteins embedded in the cell membrane that act like pores, allowing certain kinds of molecules and ions to pass through while blocking others.

Consequently, they play an important role in many biological processes in which rapid changes occur in cells, such as cardiac function, T-cell activation and pancreatic beta cell insulin release.

It’s hardly surprising, then, that much work has been devoted to working out how ion channels function. One technique is to stuff a cell into the tip of a syringe containing the ion under investigation. Apply a voltage to the cell and the current is a measure of the flow of ions across the cell membrane. Another technique is to measure the flow of ions across a synthetic cell membrane known as a black lipid layer.

Both of these techniques have yielded interesting insights but ask a cell biologist how accurate they are, and he or she will shuffle her feet and stare at the ground.

Now a new technique promises to put all others in the shade, say Leonard Hall at the University of Melbourne in Australia and a few mates. The idea is based on how fast electron spins decohere in a nitrogen atom inside a nanodiamond. In recent years, physicists have become hugely excited about these so-called nitrogen vacancies because they are easily controlled using microwaves or light. They are also isolated from their environment by the carbon matrix.

Hall and co’s idea is to place the nanodiamand on the tip of an atomic force microscope and move it to within a hair’s breadth of an ion channel in a cell membrane. The electron spins in the nitrogen vacancy are then set in a particular state by zapping them with a sequence of microwave pulses.

When the channel opens, the flow of ions through it generates a tiny magnetic field which interacts with the electrons spin, causing them to decohere. This can be easily monitored by looking for the fluorescence produced by the nitrogen vacancy.

The technique should be able to measures the flow of ions through the channel with microsecond resolution, says the group. That kind of accuracy is unprecedented. And the beauty of it is that nanodiamond doesn’t touch or interfere with the channel which can operate in its (more or less) natural environment.

Cell biologists ought to be turning back flips over this but it is the drugs companies that really stand to benefit. A large proportion of drugs target ion channels, so knowing exactly what effect they have should be an important part of the drug discovery process. The new technique could make that possible.

For the moment, the work is at a theoretical stage, investigating the feasibility of the idea. But Hall and mates say it looks possible with current technology. That means it ought to be only a matter of months before we see the first results.

Ref: arxiv.org/abs/0911.4539: Monitoring Ion Channel Function In Real Time Through Quantum Decoherence