Fig. 6: Septin5 depletion increases the number of granules associated with L-type Ca²⁺ channels and increases the Ca²⁺ sensitivity of granule fusion.

a Normal and T2D human β-cell infected with granule marker NPY-tdOrange2 and loaded with Ca²⁺ sensor 2 μM Fluo5F as well as EGTA-AM stimulated with high K⁺ (75 mM). The localized Fluo5F signal indicated the Ca²⁺ influx sites after depolarization. b, c Fusion events of granules associated with L-type Ca²⁺ channels in human normal (b) and T2D (c) β-cells. d, e Septin5 depletion improves GSIS in human T2D islets. The corresponding area-under-the-curve (AUC) analysis was summarized in (e) (Data from n = 3 biologically independent experiments were represented as mean ± SEM). f–g The glucose-stimulated insulin secretion of GK rat islets is assessed by perfusion. 25 islets exposed to 2.8 mM glucose for 10 min, followed by 16.7 mM glucose for 30 min, during which the sample collected every 2.5 min. The corresponding AUC analysis was summarized in (g) (Data from n = 3 biologically independent experiments were represented as mean ± SEM). h–k Septin5 deletion increases Ca²⁺ sensitivity to both low (h, i) and high (j, k) calcium concentrations but did not cause any change in calcium channel opening or density (Supplementary Fig. 8f, g). h The whole-cell capacitance change recorded during direct application of 200 nM free Ca²⁺ via patch pipette into human β-cells. i The average capacitance increments in control and Septin5 KD cells at 150 s following initiation of Ca²⁺ infusion and normalized to initial cell size. j Exocytosis was elicited by flash photolysis and monitored by whole-cell membrane capacitance measurement. Averaged capacitance changes from control (black, n = 11) and Septin5 KD (gray, n = 11) cells. Arrow indicates the flash time. k Averaged amplitudes of the highly calcium-sensitive pool from control (black) and Septin5 KD (white) cells respectively (n = 11 from three independent experiments). Statistical significance was assessed by a two-tailed Student’s t-test (the precise statistical results indicated in figures). For boxplots, boxes indicate 25th and 75th percentiles, the lines within boxes mark medians, whiskers above and below boxes indicate the 90th and 10th percentiles. Source data are provided as a Source Data file.