RESOLUTION OF CELLULAR COMPARTMENTS INVOLVED IN MEMBRANE-POTENTIAL CHANGES ACCOMPANYING IGE-MEDIATED DE-GRANULATION OF RAT BASOPHILIC LEUKEMIA-CELLS

The overall membrane potential of rat basophilic leukemia cells (RBL-2H3) calculated from the transmembrane distribution of the lipophilic, 3H-labeled cation tetraphenylphosphonium ([3H]TPP+) was resolved into its mitochondrial and plasma membrane potential components. Using the mitochondrial uncoupler carbonylcyanide-p-trifluormethoxyphenyl hydrazone (FCCP) which collapses the mitochondrial potential, it was shown that about 1/3 of the overall potential resulted from the mitochondrial contribution. Degranulation of the RBL cells induced by 2 different IgE-cross-linking agents (specific antigen and anti-IgE antibodies), was accompanied by, and well correlated with, a decrease in the overall potential. Evaluation of the source of these observed potential changes revealed that the FCCP-insensitive fraction of the overall-insensitive fraction of the overall potential, .DELTA..psi.P, (representing the plasma membrane potential), was not affected. The FCCP-sensitive component due to the mitochondrial potential decreased when receptor crosslinking increased. The observed decrease in the overall potential is most probably a secondary event in the sequence leading from stimulus to secretion. Exposure of the RBL cells either to a high external concentration of K+ or to a high amount of external TPP+, both causing depolarization, failed to trigger degranulation. The apparent decrease in the measured overall potential is a reflection of the mitochondrial membrane depolarization. The latter is most probably caused by mitochondrial Ca2+ uptake initiated by the increase in the intracellular concentration of Ca2+ which follows cells activation.