Characterization of the ion channel activity in planar bilayers containing IgE-Fc epsilon receptor and the cromolyn-binding protein.

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Abstract
Electric conductance was studied across micropipette‐supported planar lipid bilayers, reconstituted with IgE‐Fc epsilon receptor and the cromolyn‐binding protein (CBP) isolated from membranes of rat basophilic leukemia cells (RBL‐2H3). Currents were observed following the addition of aggregating agents, specific for either of the two proteins. The results show that the two proteins are necessary and sufficient for the opening of cation channels. Both aggregation of Fc epsilon receptor via IgE with a specific antigen and of CBP by anti‐CBP induce channels with similar conductances and open‐time distributions. In the presence of 1.8 mM calcium, the most frequently observed channels have a conductance of 1‐2 pS. At 100 mM calcium conductance increased to 4‐5 pS. Channels induced by antigen were susceptible to blocking by the anti‐allergic drug cromolyn. These results suggest that CBP acts as the core of the cation channel and that the channel conductance and open‐time characteristics are independent of the mode of aggregation.