A calcium-dependent cation channel in mast cell granule membranes reconstituted into a lipid bilayer

Secretory granules isolated from rat peritoneal mast cells were reconstituted into a lipid planar bilayer and membrane current was measured. A novel calcium- and voltage-dependent cation channel with single-channel conductances of 80 pS for fully open and 60 pS for sub-conducting states was detected. This channel opened only when potential of the cis compartment, which corresponds to the cytoplasmic side in the cell, was positive with respect to the trans compartment and only when Ca concentration of the cis compartment was higher than 10(-7) M. The open channel probability further increased, depending on the concentration of Ca. The physiological role of this channel remains to be determined.