Figure 4.

Effect of GTP[γS] and GDP[βS] on Ca²⁺-independent and Ca²⁺-stimulated exocytosis. (A) Change in C_m for 20 min after the start of cytosolic dialysis with 20 mM BAPTA and no added Ca²⁺ (top trace), and with addition of 100 μM GTP[γS] (middle trace), or 500 μM GDP[βS] (bottom trace). Numbers at start of traces indicate resting capacitance (in pF) measured upon formation of the whole-cell configuration. Increase in C_m for the cells shown was 4, 3, and 7%. (B) Change in C_m for 20 min after the start of cytosolic dialysis as in A but with 1 μM free Ca²⁺. Increase in C_m for the cells shown was 16, 10, and 1%. (C) Relative change in C_m (% C_m) determined 20 min after the start of cytosolic dialysis with 20 mM BAPTA and no added Ca²⁺ (n = 10) and with addition of 100 μM GTP[γS] (n = 6) or 500 μM GDP[βS] (n = 9) (Left) and 1 μM Ca²⁺ (n = 8) and addition of 100 μM GTP[γS] (n = 6) or 500 μM GDP[βS] (n = 6) (Right). Bars represent SEM.