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Authored by: Paul Taylor, Boehringer Ingleheim Inc.
Patch clamping is a technique that has been in existence since the late 1970’s and is used to study ion channel properties. It is estimated that ion channel genes in the human genome comprise 1.3% of the total, or approximately 400. Classical manual patch clamp techniques are quite slow and, while high in information content, allow a maximum of only ~20 runs/day. The methodology consists of pressing a glass microelectrode against a "patch" of cell membrane and forming a gigaseal with billions of ohms of resistance. A small amount of suction is applied by the pipet and results in a seal that is so tight that any ion flow into the pipet originates from an open ion channel. The micro current that results is detected via the application of an amplification step. To address throughput issues, automated patch clamp systems have been developed that allow testing of hundreds to thousands of cells each day. In these systems, the individual glass electrodes have been replaced with glass chips with small holes and include fluidic control, automated suction mechanisms and a detection step all under sophisticated software control. The systems also include rapid solution switching (<50 ms) for application of drug screening with fast ligand gated ion channels. One disadvantage is that cells need to have stable and high expressions of the ion channel of interest and also need to be homogenous and healthy – not all cell types fit these criteria. A common application of automated patch clamping is for secondary safety profiling with hERG (human ether-a-go-go-related gene) potassium channels. Briefly, hERG has been identified as the molecular target of drugs which are associated with an increased risk of a cardiac arrhythmia known as torsade de pointes.
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