Patch-clamp measurement of ICRAC and ORAI channel activity.

Depletion of internal Ca(2+) stores activates store-operated Ca(2+) channels. The most prominent members of this class of channels are Ca(2+) release-activated Ca(2+) (CRAC) channels, which are present in a variety of cell types including immune cells. CRAC channels are composed of ORAI proteins, which are activated by endoplasmic reticulum-bound STIM proteins on Ca(2+) store depletion. The underlying Ca(2+) current is called ICRAC, which is required for many cellular functions including T-cell activation, mast cell activation, Ca(2+)-dependent gene expression, and refilling of internal Ca(2+) stores. To analyze ICRAC or the Ca(2+) current through heterologously expressed ORAI channels, whole-cell patch clamp is the technique of choice. It allows the direct analysis of ion currents through CRAC/ORAI channels. The patch-clamp technique has been used to determine selectivity, permeability, rectification, inactivation, and several other biophysical and pharmacological properties of the channels, and is the most direct and reliable technique to analyze ICRAC.