Figure 2. SUMOylation increases the α-cell exocytotic response to membrane depolarization, and upregulates L-type Ca²⁺ currents.

We measured exocytosis as increases in membrane capacitance in mouse and human α-cells, positively identified by glucagon immunostaining, during a series of 10 membrane depolarizations from −70 mV to 0 mV. Representative (A) and quantified (B) responses of mouse α-cells infected with green fluorescent protein (Ad-GFP; open circles) or SUMO1 (Ad-SUMO1; black circles)). Representative (C) and quantified (D) responses of mouse α-cells infected with a scrambled control (Ad-shScramble; open squares) or an shRNA sequence targeted against SENP1 (Ad-shSENP1; black squares)). Representative (E) and quantified (F) responses of human α-cells infected with Ad-GFP (open circles) or Ad-SUMO1 (black circles). Representative (G) and quantified (H) Ca²⁺ currents from human α-cells infected by Ad-GFP or Ad-SUMO1, elicited by a single depolarization from −70 mV to 0 mV, in the absence or presence of 5 μm isradipine. *P < 0.05, **P < 0.01, ***P < 0.001 for comparisons with the control.