Glucagon potentiates insulin secretion via β-cell glucagon receptors (GCGR) at physiological doses of glucose. (A,B) Effects of MK0893 or Exendin 9-39 on 100 nM glucagon-induced insulin secretion of isolated mouse islets in 20 mM (A) and 5 mM glucose (B) (n = 5–7 per group). Glucagon is abbreviated as GCG, MK0893 is abbreviated as MK, and Exendin 9-39 is abbreviated as Ex9 in the figures. (C,D) Effects of MK0893 or Exendin 9-39 on 100 nM glucagon-increased RRP size of single β-cells isolated from C57BL/6J mice in 20 mM glucose (C) or 5 mM glucose (D) (n = 16–25 per condition). (E) Perforated patch on a α-β cell cluster. Left panel: schematic depicting the dissociation of GYY mouse islets into a α-β cell cluster or a single β-cell. Right panel: representative image of a perforated patch performing on a α-β cell cluster. (F,G) Effects of MK0893 and Exendin 9-39 on the RRP size of β-cells in α-β cell clusters isolated from GYY mice in 20 mM glucose (F) or 5 mM glucose (G) (n = 16–23 per condition). Statistical significance was evaluated using Student’s t-test for single Gaussian-distributed datasets or the Mann–Whitney rank-sum test for non-single Gaussian-distributed datasets. * p < 0.05, ** p < 0.01, *** p < 0.001.