INTERACTION OF TOLUIDINE BLUE AND RAT MAST CELLS: HISTAMINE RELEASE AND UPTAKE AND RELEASE OF THE DYE

¹ Department of Pharmacology, Division of Basic Health Sciences, Emory University, Atlanta, Georgia

Mast cells from rat serous fluid released histamine in response to toluidine blue in a selective manner similar to that induced by compound 48/80, i.e., rapid (15 seconds), concentration-dependent, no release of lactic dehydrogenase, inhibited by 5°C (reversibly), by 45°C (irreversibly) and by ninhydrin or N-ethylmalemide. Mast cells took up toluidine blue; initial uptake was rapid (50% of uptake in less than 30 seconds) and was related to histamine release, i.e., it was augmented by prior treatment with 48/80 or Triton X-100 and was depressed by 45°C. Second phase uptake reached a maximum in 15 to 30 minutes and was unrelated to histamine release, total uptake being alike in normal cells and cells treated with 48/80 or Triton. The slow uptake was inhibited at 5°C but not at 45°C; it was not antagonized by ninhydrim or N-ethylmaleimide. Bound toluidine blue was not released from mast cells by 48/80 but was released by Triton X-100 in a particulate fraction of cells that sedimented at 5000 x g. It was concluded that toluidine blue can be used as a marker for mast cell granules. On the basis of the lack of release of toluidine blue in response to 48/80, one can conclude that the granules that are exteriorized by the process of exocytosis are trapped in channels connected to the extracellular fluid. Thus, rapid release of histamine can occur by exchange with extracellular cations, but most of the granules themselves remain entrapped in the cell cavities.