Figure 6. Intracellular Ca²⁺ Responses of α Cells within Intact Human Islets Are Regulated by a K_ATP Channel-Dependent Mechanism.

(A) Ca²⁺ responses measured in two human α cells within the same islet at 0.5 mM and 11 mM glucose (glu), in the presence of 2 μM diazoxide (diaz).

(B) Summary of the Ca²⁺ responses at 0.5 mM glucose, at 11 mM glucose, in the presence of glucose (11 mM) and diazoxide (2 μM), and following the removal of diazoxide, but in the continued presence of 11 mM glucose.

(C) The re-activation of human α-cell Ca²⁺ responses by 2 μM diazoxide was reversed upon application of the K_ATP channel antagonist tolbutamide (100 μM).

(D) The effects of increasing concentrations of diazoxide on the Ca²⁺ response of a human α cell and β cell within the same islet exposed to 11 mM glucose. At the end of the experiment, diazoxide was withdrawn and glucose lowered to 0.5 mM.

(E) Dose-response curve for the effect of diazoxide on α-cell Ca²⁺ responses. The grey horizontal line indicates the response with 11 mM glucose alone.

*, p < 0.05; **, p < 0.01; ***, p < 0.001, compared with controls, unless otherwise indicated.