Figure 1. SUMO1 increases α-cell excitability and upregulates voltage-dependent Ca²⁺ currents.

We measured action potentials (APs) from mouse α-cells in the perforated patch condition, positively identified by glucagon immunostaining, with 0 pA and −2 pA current injection. A, representative APs from three different α-cells transduced with green fluorescent protein (Ad-GFP). B, representative APs from three different α-cells transduced with SUMO1 (Ad-SUMO1). Upregulation of SUMO1 increased AP half-width (C) and firing frequency (D), decreased the firing threshold (E), and increased AP amplitudes without affecting peak potential (F, G). We then measured voltage-dependent Na⁺ (H), K⁺ (I) and Ba²⁺ (J) currents from mouse α-cells infected with Ad-GFP (open circles) or Ad-SUMO1 (black circles), positively identified by glucagon immunostaining, in the whole-cell configuration. *P < 0.05, **P < 0.01, ***P < 0.001 for comparisons of Ad-SUMO1 with Ad-GFP.