Voltage tester for beating heart cells
Electric signals play a major role in human cells. For instance, nerve cells utilise electric impulses to transmit information along their stolons and the body controls the contraction of muscles with electric pulses. These impulses are generated when specialised channel proteins in the outer shell of the cell open themselves and allow molecules with electric charges to enter or exit the cell. These proteins are called ion channels. Since the seventies, a method is generally available to measure the activities of these channels. But so far this method has been applied to non-moving cells. Engineers from the ETH university of Zurich and biologists of the Bern university now have further developed this method, enabling users to measure moving cells such as beating heart muscle cells in a cell culture dish.
With the existing method, users introduce a glass pipette to the outer membrane of the cells. The opening at the point of the pipette is small enough to cover just a small spot of the cell surface. Ideally, on this spot is exactly one ion channel. The pipette is filled with a conductive liquid and an electrode. This makes it possible to measure differences in the electric charge between inside and outside of that cell and thus the electric voltage. Likewise it is possible to detect quick voltage changes caused by the activities of these ion channels. The method is called patch-clamp technique because the pipette clamps a tiny piece of the cell membrane.
A research team of headed by Tomaso Zambelli from the Institute for Biomedical Technology of the ETH university and Hugues Abriel from the department of clinical research of the Bern university combined the patch-clamp technique with an atomic force microscope. The measuring tip is mounted on top of a flexible fixing, enabling it to scan the surface of a microscopic object. While in commercially available patch-clamp measuring products the pipette is moved manually; the few automated tests hitherto required that the cells are not moving which ruled out tests on heart cells.
The Swiss researchers utilised the atomic force microscope to control the movement of the micro needle, enabling to perform equidistant moves across the surface of the cells. "This makes the contact between needle and cell much more stable", said Zambelli. "It enables us to perform measurements over longer periods and what’s more, we even can examine cells that are moving." Thus, the team for the first time succeeded to measure voltage deviations over ion channels of beating heart muscle cells. It is possible to develop an automated measurement process based on the achievements of the Swiss team. This would make it possible to measure random cells regardless of their shape and size, Zambelli said.
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