Patch clamp methods for studying calcium channels.

The patch clamp technique, which was introduced by Neher and Sakmann and their colleagues in 1981, has allowed electrophysiologists to record ion channel activity from most mammalian cell types. When well-established precautions are taken to minimize electrical and mechanical fluctuations, current transients as small as 0.5pA and as brief as 0.5ms can be measured reliably in cell-attached patches of plasma membrane with a polished glass pipette when it forms a giga-ohm seal with the membrane. In many cases, this is sufficient to watch individual channel proteins open and close repeatedly in real time on metabolically intact cells. No other technique currently provides a more precise or detailed view of the function and regulation of calcium channel gating. If antibiotics are added to the pipette to permeabilize the membrane underneath to small monovalent cations, thereby allowing the entire cell to be voltage-clamped without disrupting its contents, the integrated activity of all the calcium channels in the surface membrane can be measured.