A cAMP-GEFII Agonist Stimulates Exocytosis in α-Cells A, Depolarizations (5–250 msec) from −70 mV to 0 mV were applied to single mouse α-cells (only 50 msec and a 250-msec shown for clarity) under control conditions (a); in the presence of 100 μm 8CPT-2Me-cAMP (b); and in the simultaneous presence of 8CPT-2Me-cAMP and 0.5 mm Rp-cAMPS (c). B, Relationship between pulse duration (t) and increase in membrane capacitance (ΔC_m) under control conditions (black squares), in the presence of 100 μm 8CPT-2Me-cAMP (gray circles) and in the simultaneous presence of 8CPT-2Me-cAMP and 0.5 mm Rp-cAMPS (white triangles). Data are mean values ± sem of seven to 24 experiments. ^a, P < 0.05; ^b, P < 0.01; and ^c, P < 0.001 for comparison between 8CPT-2Me-cAMP and control; ^d, P < 0.05; and ^e, P < 0.01 for comparison of the combination of 8CPT-2Me-cAMP and Rp-cAMPS with control.