Figure 1. Equivalent Ca²⁺ influx results in more insulin secretion in immature β cells.

Handpicked islets were used for secretion and Ca²⁺ assays. (A) The percentage of insulin secretion induced by 25 mM KCl in islets at 0 (left columns) or 2.8 mM (right columns) glucose. Data from three time points, before KCl stimulation (“0”), 10 minutes or 45 minutes (m) with KCl stimulation (“10” or “45”) were presented. The data at “0” minute represent insulin secretion within a 45 minutes time window without KCl stimulation. The indicated statistical analysis (top brackets) was calculated between P1 and P12 islets. (B) Insulin content per β cell, assayed with purified β cells of Rip^mCherry mice. (C) Average islet cytoplasmic Ca²⁺ responses to 25 mM KCl-induced depolarization in 2.8 mM basal glucose; these responses were assayed with Fura2AM. (D) Quantification of the KCl-induced islet Ca²⁺ response defined with area-under-curve after KCl addition (from 2–8 minute). (E) The greatest total Ca²⁺ levels reached in islets of different ages stimulated by 25mM KCl. (F) Insulin secretion induced by ionomycin (Iono) in P1 and adult islets. Diazoxide (Dia) was included in these assays. (G) Islet DSIS with or without glucose-induced degranulation, achieved by incubating islets in 5.6 mM glucose for one hour prior to DSIS. (*: P< 0.05. T-test).