Secretory granules of heparin-containing rat serosal mast cells also possess highly sulfated chondroitin sulfate proteoglycans.

Rat serosal mast cells, which synthesize only heparin proteoglycans as detected by intrinsic labeling with [35S]sulfate, were analyzed for the presence of intracellular chondroitin sulfate proteoglycans by chemical and immunochemical means. Rat serosal mast cells of greater than 99% purity were treated with Zwittergent 3-12 and 4 M guanidine HCl, and the extracted nonradiolabeled proteoglycans were purified by density gradient centrifugation. As assessed by quantification of the unsaturated disaccharides released from the proteoglycans by chondroitinase ABC treatment, 10(6) rat serosal mast cells contained 2.4-4.5 micrograms of chondroitin sulfate proteoglycans. Analysis of the chondroitinase ABC digests by high performance liquid chromatography revealed the unsaturated disaccharides delta Di-4S, delta Di-diSB, and delta Di-diSE which were derived from GlcA----GalNAc-4-SO4, iduronic acid-2-SO4----GalNAc-4-SO4, and GlcA----GalNAc-4,6-diSO4, respectively. The molar ratio of the monosulfated to disulfated disaccharides was approximately 2:1 with delta Di-diSE greater than delta Di-diSB. When analyzed with a mouse anti-chondroitin sulfate monoclonal antibody and fluorescein-labeled F(ab')2 goat anti-mouse IgG, approximately 91% of permeabilized and chondroitinase ABC-treated cells in the mast cell preparations exhibited intracellular fluorescence, and the pattern of staining indicated that the chondroitin sulfate molecules were located in the secretory granules. The specificity of the monoclonal antibody for the unsaturated double bond created by chondroitinase ABC treatment of the proteoglycan in situ was established by the absence of fluorescence when the chondroitinase ABC step was omitted or when heparinase digestion was substituted for chondroitinase ABC. Furthermore, the ability of the anti-chondroitin sulfate monoclonal antibody to mediate fluorescence in situ was markedly reduced by absorption with solid-phase chondroitin sulfate proteoglycan that had been chondroitinase ABC-treated, but not by absorption with undigested proteoglycan or with solid-phase heparin. The highly sulfated chondroitin sulfate proteoglycans of rat serosal mast cells are the same type synthesized by the rat mucosal mast cell subclass.(ABSTRACT TRUNCATED AT 400 WORDS)