Depletion of intracellular calcium stores activates an outward potassium current in mast and RBL-1 cells that is correlated with CRAC channel activation.

Highly Ca2+ selective Ca2+ channels activated by store depletion have been recently described in several cell types and have been termed CRAC channels (for calcium release-activated calcium). The present study shows that following store depletion in mast and RBL-1 cells, monovalent outward currents could be recorded if the internal solution contained K+ but not Cs+. The activation of the outward K+ current correlated with the activation of ICRAC, in both time and amplitude, suggesting that the K+ current might be carried by CRAC channels. The amplitude of the outward current was increased if external Ca2+ was reduced or replaced by external Ba2+. The outward K+ conductance might have a physiological role in maintaining the driving force for Ca2+ entry during the activation of CRAC channels.