Cell association of complexes of chymase, heparin proteoglycan, and protein after degranulation by rat mast cells.

Abstract Complexes of chymase, heparin, and certain undefined proteins that reside in rat mast cell secretory granules are poorly soluble in physiologic buffer and remain associated with mast cells after coupled activation and secretion of dissociable soluble mediators, such as β-hexosaminidase and histamine. Purified mast cells activated immunologically or with the calcium ionophore A23187 retain granule core material in cell surface labyrinths as demonstrated by electron microscopy. In order to solubilize and extract this core material, activated mast cells were washed with 1 M NaCI, a procedure that does not impair the integrity of plasma membrane barriers as assessed by the failure to release lactate dehydrogenase (LDH) from resting or activated mast cells. High salt treatment of resting cells caused swelling of cytoplasmic granules, whereas high salt treatment of activated cells caused the extruded granule core material to lose structure and become disassociated from the mast cell surface, as revealed by electron microscopy. Salt treatment of activated mast cells with anti-IgE also increased the net percent release ratios of chymase and heparin to β-hexosaminidase from 0.17 to 0.76 and from 0.24 to 0.51, respectively, indicating either that complexes of heparin and protein were only partially solubilized by the high salt conditions or that there was some re-uptake after release. Furthermore, net protein detected as released material from mast cells activated in a protein deficient medium with A23187 increased from 30 to 53 µg/106 mast cells with salt treatment. Resting and activated mast cells have the same content of chymase activity, 0.56 ± 0.15 U or 24 ± 6 µg, indicating that there is no significant activation of enzyme precursor forms with mast cell activation and that chymase accounts for about 40% of the secretory granule protein in these cells. Twenty-eight micrograms of heparin and 1.3 U of β-hexosaminidase (1 µg) were also detected in 106 mast cells. Thus, approximately one-half of the secretory granule proteins are functionally undefined, and these as well as the concentration and prolonged presentation of complexes containing heparin and chymase at the cell surface of activated mast cells may be important in the chronicity of the host response to mast cell activation.