IMMUNOGLOBULIN-E RECEPTOR-ACTIVATED CALCIUM CONDUCTANCE IN RAT MAST-CELLS

1. The nystatin perforated-patch method was used to record macroscopic currents from antitrinitrophenyl (TNP) immunoglobulin E (IgE)-sensiti zed rat basophilic leukaemia (RBL-2H3) cells at 37 degrees C. 2. An in wardly rectifying Ca2+ current (I-Ca) was activated upon stimulation w ith the multivalent antigen trinitrophenylated bovine serum albumin (T NP-BSA). Induction of I-Ca was not observed at room temperature. I-Ca was reversed and reinduced upon cyclical addition of the monovalent ha pten dinitrophenyl (DNP)-lysine and multivalent antigen, indicating th at a specific interaction of antigen with IgE was required to elicit I -Ca. 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+. I-Ca di d not exhibit time-dependent opening (less than or equal to 1 ms) in r esponse to hyperpolarizing voltage steps to -100 mV, although it did a ccumulate steady-state inactivation of similar to 40-50 % over 100 ms. 4. Two inorganic blockers of antigen-stimulated Ca-45(2+) influx and secretion, La3+ and Zn2+ inhibited I-Ca by similar to 50 % at concentr ations known to produce 50 % block of Ca-45(2+) influx. In contrast, c romolyn sodium (0.5 mM) and the L-type Ca2+ channel antagonist nitrend ipine (5 mu M) had no effect on I-Ca. 5. I-Ca also was induced by the intracellular Ca2+ mobilizer thapsigargin. Because the actions of thap sigargin and antigen were not additive, IgE receptor cross-linkage app ears to activate the recently described capacitative Ca2+ entry channe ls.