Labelling of the inner side of granules membrane during exocytosis. A method to differentiate secretion processes.

A fluorescence method to monitor quantitatively exocytosis phenomena in suspensions of intact cells was investigated, on the basis of the particular incorporation properties of a specific plasma membrane fluorescent label trimethylammonium-diphenylhexatriene (TMA-DPH). The method was tested with purified peritoneal mast cells stimulated by compound 48/80. Kinetics and dose-dependent response to compound 48/80 could be described accurately by the TMA-DPH fluorescence increase accompanying the exocytosis phenomenon, as controlled by conventional titrations of the released histamine. TMA-DPH bound to the outer side of the plasma membrane of resting cells and additively to the inner side of granules connected by pores to the exterior of stimulated mast cells.