Changes in membrane potential induced by compound 48/80 in the peritoneal mast cells of rats

The changes in membrane potential induced by compound 48/80 were studied using rat peritoneal mast cells. The mean resting membrane potential of rat mast cells was -12.3 ± 0.7 mM. When compound 48/80 was added to the mast cells, the cells were degranulated approximately 120 sec after the addition of the drug, after which immediate depolarization occurred. Degranulation of mast cells was not observed, even under the depolarization or hyperpolarization conditions caused by the replacement of a high K⁺ medium or the removal of K⁺ from the medium, respectively. Under both conditions, when compound 48/80 was added to the mast cells, degranulation was observed. Abrupt and marked depolarization was induced 30-60 sec after compound 48/80 was added. In addition, repolarization followed by gradual depolarization was observed without degranulation in mast cells treated with cytochalasin D after the addition of compound 48/80. These results suggest that the mast cells were depolarized by compound 48/80 independently of degranulation. It is also feasible that the gradual depolarization and repolarization induced by compound 48/80 in mast cells pretreated with cytochalasin D participated in the extracellular Na⁺ and Na⁺/K⁺-pump, respectively.