We measured exocytosis as increases in membrane capacitance in mouse α-cells, identified by glucagon immunostaining, in response to membrane depolarization in the whole-cell configuration. A, representative capacitance responses of α-cells infected with green fluorescent protein (Ad-GFP; black traces) or SUMO1 (Ad-SUMO1; red traces) without cAMP included in the patch pipette and following treatment with adrenaline or forskolin as indicated. B, cumulative capacitance response of α-cells infected with Ad-GFP (open bars) or Ad-SUMO1 (black bars). Ad-SUMO1 was unable to increase α-cell exocytosis in the absence of cAMP, but this response was restored following treatment with forskolin or adrenaline. *P < 0.05, **P < 0.01, ***P < 0.001 for comparisons with the respective control, or as indicated.