Table 2.

Secretion from permeabilized peritoneal- and ES cell-derived mast cells  Peritoneal mast cells (PMCs; isolated as described in the legend to Table 1) and isogenic ⁺/⁺ and −/− ES cell-derived mast cells, pretreated with SLO at 0°C were permeabilized by transfer to a buffer (pH 6.8) containing 1 mM MgATP and 0.1 mM EGTA to reduce free [Ca²⁺] to below 10⁻⁸M. This treatment induces a time-dependent rundown of secretion efficiency that is a function of progressive loss of a phosphoinositide pool required for the exocytotic event (Pinxteren et al., 1998, 2001). At the indicated rundown times, cells were stimulated by a secretagogue cocktail containing 100 μM GTPγS and 3 mM Ca-EGTA formulated to regulate pCa5. After a 10-min incubation, the systems were quenched with an ice-cold salts buffer containing 5 mM EGTA. The cells were sedimented and the supernatants were sampled and assayed for secreted hexosaminidase. Data points (%) represent mean values ± SEM (n = 4) normalized to maximum secretion (100%) determined in absence of rundown (time 0). PMCs serve as positive control.

Time of rundown	0 min	2 min	10 min	30 min
PMCs	100	57.7  ± 2.8	25.3  ± 2.0	2.6  ± 0.3
+/+	100	55.7  ± 12.1	23.7  ± 3.0	4.0  ± 1.5
−/−	100	51.2  ± 3.6	22.6  ± 3.1	2.6  ± 1.1