Electrical activity and [Ca²⁺]_i in δ-cells. Poor temporal correlation between δ-cell action potential firing and [Ca²⁺]_i dynamics. (A) Electrical activity (V_m, middle) and changes in [Ca²⁺]_i (ΔF/F0; bottom) measured simultaneously from an SST-GCaMP3 δ-cell at 1 mM and 10 mM glucose (top). [Ca²⁺]_i transients temporally correlated to action potentials are highlighted in red (“triggered” events). (B) Segments of the recording in A in the presence of 10 mM glucose (i) and after its washout (ii) displayed on an expanded time scale. Dotted vertical lines indicate [Ca²⁺]_i spikes that correlated with action potentials. Representative of four similar independent experiments in four different islets from four mice. (C) Average integrated [Ca²⁺]_i transients (AUC) of triggered (139 events in nine independent experiments) and spontaneous events (241 events in nine independent experiments). (D) Average spike amplitude of [Ca²⁺]_i transients (pAUC) when islets were superfused with 10 mM glucose (54 events in four independent experiments) and during the washing out of the glucose stimulus (14 events in four independent experiments). *, P < 0.05 vs. 10 mM glucose. In C and D, data are presented as mean values ± SEM. All experiments were conducted using perforated patch whole-cell technique.