Fig. 4: α Cell activates after β cell with a fixed time delay while β cell activates after α cell with variable time delay.

a Left: Each oscillation cycle is defined as the interval between two β cell activations (see Supplementary Fig. 3 for alternative ways to define the period T). Right: 13 features of α-β oscillation cycle are used to construct the feature matrix (columns represent features, rows represent oscillation cycles). b Left: Oscillation cycles are separated into two clusters by using UMAP, with the mean oscillation period (T) of each cluster shown (n = 658 cycles from 21 islets, the fast and slow clusters have 574 and 84 oscillation cycles, respectively). Right: Mean Ca²⁺ traces (bold line) and 15 representative traces (thin line) of fast clusters (top panel) and slow ones (bottom panel), aligned at the peaks of β cell Ca²⁺ activity (arrows). c Histogram of phase difference (Δθ), oscillation period (T), waiting time of α cells (T_βα), and Full Width at Half Maximum of α and β cells (α_FWHM, β_FWHM) in fast and slow clusters defined in Fig. S3. d Left: Scatter plot of Δθ versus T. Dashed lines indicate in-phase and anti-phase α and β oscillations. Right: Scatter plot of T_βα versus T. The blue and orange dots represent the fast and slow clusters from all 21 islets in b. The red, green, and dark blue dots represent the oscillations from fast, mixed, and slow islets shown in Fig. 5d (right panels) (See Supplementary Fig. 4b–d for scatter plots of other ways to define the period). e Left: Mean Ca²⁺ traces of α and β cells when the glucose stimulation was shifted from 3 G to 10 G. The rectangle box showed 38 α and β phase-locked oscillations. Right: T, T_βα, and Δθ of 38 oscillation cycles.