Soluble proteins as modulators of the exocytotic reaction of permeabilised rat mast cells

This study addresses the question of the role of cytoplasmic proteins in exocytosis from permeabilised rat mast cells. We have used two different methods of cell permeabilisation (ATP4- and streptolysin O) to regulate the size of the plasma membrane lesions, and thus to dictate the rate and extent of efflux of the cytosolic proteins, and compared the secretory response of the two preparations. We report evidence for the existence of two factors present in the cytosol, which affect the exocytotic mechanism in opposing manners. One of these is required for the maintenance of cell responsiveness; it is retained for more than 120 min by ATP4- -permeabilised cells but lost within 60 min from cells permeabilised by streptolysin O. The other factor, which leaks immediately from cells treated from streptolysin O, but only gradually from cells treated with ATP4-, has the effect of suppressing the affinity for both Ca2+ and guanine nucleotide in the exocytotic reaction.