Fig. 2.

IP6K1 regulates first phase of glucose-stimulated exocytosis. (A) Effects of IP6K1 or IP6K2 siRNA on insulin release were studied using dynamic incubation assays in MIN6m9 cells. There was a significant difference in insulin release between control and IP6K1 siRNA after 2 min of glucose stimulation, n = 3, ***p < 0.001, two-way ANOVA (Supplemental Table S1). (B) Insulin secretion data from panel (A) were compiled for the first 3 min, n = 3, *p < 0.05, Student's t-test. (C) Mouse islet cells were transfected with fluorescently tagged siRNA to IP6K1 or a negative control. Fluorescent cells were subjected to a train of four 500-ms depolarizations (1 Hz) using the perforated patch configuration. Increases in cell capacitance (ΔC_m) were measured at 16.7 mM glucose (16.7 G) in the extracellular medium. Recordings are representative of 5–8 experiments. (D) Histogram summarizing the average increment in cell capacitance per pulse (ΔC_m,n − ΔC_m,n−1) during the train of depolarization in cells transfected with either siRNA to IP6K1 or negative control, n = 5–8, *p < 0.05, Student's t-test. (E) Effect of siRNA to IP6K1 on total capacitance increase, n = 5–8, *p < 0.05, Student's t-test. (F) KCl mediated insulin secretion is not mediated via IP6K1. MIN6m9 cells treated with either control siRNA or IP6K1 siRNA were stimulated for 3 min with an addition of 25 mM KCl. There was a significant increase in insulin secretion in both control siRNA and IP6K1 siRNA treated group, n = 3, **p < 0.01, repeated measures two-way ANOVA followed by Bonferroni post-hoc test. (G) Basal [Ca²⁺]_i and (H) glucose (10 mM) induced [Ca²⁺]_i response were measured in control and IP6K1 siRNA-treated MIN6m9 cells (n = 3 preparations each compiled from 30 to 40 ROIs). All bars are means ± SEM. See experimental procedures for [Ca²⁺]_i data analysis.