Extended Data Fig. 7: Delta-cell response to the ionophore monensin and alterations to extracellular potassium.

a, Histograms summarizing frequency of [Ca²⁺]_i oscillations at 1 mM glucose alone, following the addition of monensin and in the presence of monensin and a cocktail of isradipine (2.5 µM), SNX482 (100 nM) and diazoxide (100 µM) n= 53 cells from 3 islets/2 mice **p<0.005, one-way ANOVA followed by Tukey’s post hoc for indicated comparisons. b, Membrane potential recordings from a δ-cell at 1 mM glucose in the absence and presence of monensin. Representative of 4 cells (n=3 mice). c, Effects of decreasing [K⁺]_o from the normal 3.6 mM to 1.7 mM. Note that the delta cell is hyperpolarized at 1 mM glucose and not electrically active. Reducing [K⁺]_o leads to further hyperpolarization. d, Relationship between [K⁺]_o and membrane δ-cell potential. This relationship indicates that the membrane potential in delta cells exposed to 1 mM glucose is principally (but not exclusively) determined by the K⁺ permeability. All data are represented as mean ± SEM.