Fig. 2.

Loss of VAMP-8, but not synaptobrevin 2 or VAMP-3, partially inhibits regulated β-hexosaminidase release from mast cells. (A and B) Mast cells derived from synaptobrevin 2^−/−, VAMP-3^−/−, and VAMP-8^−/− mice (and corresponding wild-type littermate controls) were sensitized overnight with anti-DNP-specific IgE and induced for secretion the next day by cross-linking FcεRI by using 10 ng/ml DNP–BSA for 30 min (A) or by using PMA and ionomycin together for 15 min (B). The data shown are means ± SEM of at least five independent experiments. (C) Mast cells from VAMP-8^+/+, VAMP-8^+/−, and VAMP-8^−/− mice were triggered for secretion by cross-linking FcεRI-associated IgE with different concentrations of DNP–BSA for 30 min. The data shown are means ± SEM of at least eight independent experiments. (D) Mast cells from VAMP-8^+/+ or VAMP-8^−/− mice sensitized overnight with anti-DNP-specific IgE were stimulated for various times by IgE cross-linking by using 10 ng/ml DNP–BSA. The release of β-hexosaminidase into the cell supernatant was assayed as described in Materials and Methods. The data shown are means ± SEM of two independent experiments. In all experiments shown, asterisks indicate statistically significant differences between wild-type and knockout mast cells (*, P < 0.01; **, P < 0.001).