Crosslinking of the receptors for immunoglobulin E depolarizes the plasma membrane of rat basophilic leukemia cells

Aggregation of the receptor for IgE on mast cells, basophils, and a tumor analog, rat basophilic leukemia (RBL) cells, induces a calcium-dependent degranulation of the cells. We have measured the membrane potential (ΔΨ) of RBL cells during this reaction by using the tetraphenylphosphonium ion (Ph₄P⁺) equilibration technique. We observed a 20-45% reduction in ionophore-sensitive Ph₄P⁺ accumulation. The phenomenon persisted under conditions expected to collapse the mitochondrial membrane potential, consistent with the effect being due to a change in ΔΨ of the plasma membrane. We estimated that the change reflects a depolarization of 20 mV (from -90 to -70 mV, interior negative). Whereas degranulation fails to occur in the absence of external Ca²⁺, this was not true of the depolarization, indicating that the latter was not a consequence of secretion. When aggregation of the receptor is induced by reaction of the cell-bound IgE with a multivalent antigen, the secretory reaction can be halted by adding a univalent hapten. In this case, complete repolarization occurs. Equivalent depolarization was observed in the absence of Na⁺ but was diminished when both Ca²⁺ and Na⁺ were absent. Together, the data suggest that aggregation of the receptor opens ion channels and that the latter disappear promptly when the receptors are disaggregated. It is plausible that formation of these channels leads to the entry of Ca²⁺ and is an early and critical consequence of the aggregation of the receptors, thereby leading to degranulation.