Glucose-stimulated [Ca²⁺]_i oscillations in high [K⁺]_o-depolarized δ-cells. δ-cell Ca²⁺ release from the ER is stimulated by glucose. (A) Examples of δ-cell [Ca²⁺]_i (ΔF/F₀) recorded from SST-GCaMP3 islets in response to increasing [K⁺]_o from 3.6 mM to 70 mM as indicated. Experiments were conducted with extracellular media containing (i) 1 mM glucose and (ii) 20 mM glucose in islets cultured in control RPMI medium; and (iii) 20 mM glucose in islets incubated with RPMI medium containing 10 µM thapsigargin (>1 h). (B) Summary of 70 mM [K⁺]_o-triggered δ-cell [Ca²⁺]_i (pAUC) at steady-state (gray areas in A) under the experimental conditions indicated below. *, P < 0.05 vs. 1 mM glucose and †, P < 0.05 vs. 20 mM glucose without pretreatment of thapsigargin. Data are presented as mean values ± SEM of the indicated numbers of GCaMP3-expressing δ-cells (n) from two or three mice for each experimental condition. AU, arbitrary unit.