EFFECT OF ION COMPOSITION ON THE CHANGES IN MEMBRANE-POTENTIAL INDUCED WITH SEVERAL STIMULI IN RAT MAST-CELLS

We studied, in different ionic conditions, the effect of various agent s on the membrane potential or rat peritoneal mast cells using the flu orescent probe bisoxonol. Ouabain and ionophore A23187 lead to a fast depolarization of the plasma membrane of mast cells, while compound 48 /80 and thapsigargin induced membrane hyperpolarization, which was mor e pronounced in the case of compound 48/80. When using compound 48/80, the amount of gramicidin necessary to depolarize the cells was twice the amount required in resting cells, which indicates that compound 48 /80 increases considerably the activity of the Na+/K+ pump. On the oth er hand, the ionophore A23187 elicited a clear depolarization which wa s oblated in the absence of intracellular calcium. The increase in the osmolarity of the medium causes a depolarization in the plasma membra ne of mast cells. Hypertonicity-stimulated depolarization is inhibited by removing sodium and potassium.