Immunoglobulin E receptor‐activated calcium conductance in rat mast cells.

1. The nystatin perforated‐patch method was used to record macroscopic currents from anti‐trinitrophenyl (TNP) immunoglobulin E (IgE)‐sensitized rat basophilic leukaemia (RBL‐2H3) cells at 37 degrees C. 2. An inwardly rectifying Ca2+ current (ICa) was activated upon stimulation with the multivalent antigen trinitrophenylated bovine serum albumin (TNP‐BSA). Induction of ICa was not observed at room temperature. ICa was reversed and reinduced upon cyclical addition of the monovalent hapten dinitrophenyl (DNP)‐lysine and multivalent antigen, indicating that a specific interaction of antigen with IgE was required to elicit ICa. 3. The antigen‐induced current was also carried by Ba2+ or Sr2+, and to a lesser extent by Na+, in the nominal absence of Ca2+. ICa did not exhibit time‐dependent opening (< or = 1 ms) in response to hyperpolarizing voltage steps to ‐100 mV, although it did accumulate steady‐state inactivation of approximately 40‐50% over 100 ms. 4. Two inorganic blockers of antigen‐stimulated 45Ca2+ influx and secretion, La3+ and Zn2+, inhibited ICa by approximately 50% at concentrations known to produce 50% block of 45Ca2+ influx. In contrast, cromolyn sodium (0.5 mM) and the L‐type Ca2+ channel antagonist nitrendipine (5 microM) had no effect on ICa. 5. ICa also was induced by the intracellular Ca2+ mobilizer thapsigargin. Because the actions of thapsigargin and antigen were not additive, IgE receptor cross‐linkage appears to activate the recently described capacitative Ca2+ entry channels.