The role of the Fcϵ receptor in calcium channel opening in rat basophilic leukemia cells

The role of the Fc_ε{lunate}, receptor (Fc_ε{lunate}R), isolated from rat basophilic leukemia cells (line RBL-2H3) in antigen induced Ca⁺⁺ channel opening has been studied by following ion conductance in reconstituted model membranes. Planar bilayers were constructed from lipid vesicles containing the purified Fc_ε{lunate}R alone, or together with the cromolyn binding protein (CBP). Changes in conductivity of these bilayers were measured as a monitor for channel activity, following specific aggregation of Fc_ε{lunate}R. Antigen-induced, Fc_ε{lunate}R mediated channel activity could only be elicited in membranes containing both proteins. This conductance was abrogated upon disaggregating the complexes with a monovalent hapten (ε{lunate}-N-DNP-l-lysine). No channel activity was observed following antigen-induced aggregation of Fc_ε{lunate}R if CBP was not present in the bilayer. The single channels recorded were of ≈2 pS conductance. The open-time values varied significantly with individual experiments and depended on the protein composition of the membrane and the nature of the aggregating agent. These observations strongly indicate that the Fc_ε{lunate}R isolated from RBL cells does not form cation (Ca⁺⁺) channels by itself. Furthermore, in line with earlier reports, the present data suggest that the CBP is responsible for this activity, and that it interacts directly with Fc_ε{lunate}R to open channels upon aggregation.