FIG. 3.

Leptin inhibits Ca²⁺ signals induced by low glucose concentrations in αTC1-9 cells and mouse α-cells. Leptin (6.25 nmol/l) blocks or reduces the frequency of Ca²⁺ signals induced with 0.5 mmol/l glucose in αTC1-9 cells (A) and α-cells (B) (n = 13 and 16, respectively). Images show a culture of αTC1-9 cells (A) and an intact mouse islet (B) loaded with the Ca²⁺-sensitive probe Fluo-4. Islet images were acquired by confocal microscopy from an optical section close to the equatorial plane. Several individual cells were easily identified at the periphery of the islet (white arrows). C: Average frequency of Ca²⁺ oscillations with 0.5 mmol/l glucose (control) and in the presence of leptin. D: Effect of 0.625 nmol/l leptin in islet α-cells (n = 20; n = 52 for αTC1-9 cells, not shown). E: Frequency (%) of Ca²⁺ signals after stimuli compared with control conditions. F: Leptin inhibits Ca²⁺ signaling in isolated islet α-cells (n = 11). The effect of adrenaline, which is characteristic of this islet cell type (32), is also shown. Data in C and E are shown as means ± SE. *Statistically significant (P < 0.05) compared with control. Adren, adrenaline; G, glucose; Lept, leptin. Scale bar: 20 μm. (A high-quality representation of this figure is available in the online issue.)