FIG. 5.

Simultaneous measurement of [Ca²⁺]_c (FuraPE3) and [Ca²⁺]_ER (D4ER) reveals that in some (A–D and F–H), but not all (E and I), β-cells from SERCA3^+/+ mice, stimulation with high [KCl] or tolbutamide induces a CICR that is detectable by the antiparallel changes in [Ca²⁺]_c and [Ca²⁺]_ER. The perifusion medium contained 15 mmol/L glucose (G15) and 250 µmol/L Dz (A–C, F, and G–I), or 6 mmol/L glucose (G6) (D and E). A–C and G: β-Cells were stimulated with the indicated [KCl]. D and E: β-Cells were stimulated with 250 µmol/L tolbutamide (Tolb). F: β-Cells were submitted to pulses of 4.8 (K4.8) and 45 mmol/L KCl (K45) applied at a frequency (two per minute) and with a duration indicated on the top of the panel and mimicking the spontaneous oscillations of the electrical activity observed in islets stimulated by 10 mmol/L. H and I: β-Cells were submitted to two pulses of 45 mmol/L KCl (K45) of 3 and 5 s when indicated by the arrows. This illustrates the extremely fast uptake capacity of the ER as a [Ca²⁺]_ER rise was already observed during a 3-s depolarization with K45. Values are representative traces for 33/35 (A), 31/51 (B), 6/51 (C), 28/38 (D), 10/38 (E), 34/41 (F), 10/17 (G), 2/35 (H), and 33/35 (I) cells from three experiments with three islet preparations.