Figure 3.
Dysregulated α cell, β cell, and δ cell Function in Islets Lacking DBP
(A and B) Proportion of α cells showing activityat low (0.5 mM) glucose is decreased in DBP−/− islets (A), although Ca2+ amplitude is increased in responsive cells (B) (n = 46–30 islets, 4 animals; Mann-Whitney test).
(C) Representative images and traces showing loss of α cell activation in DBP−/− islets (scale bar represents 40 μm; n = 46–30 islets, 4 animals).
(D and E) Proportion of β cells showing activity at low (0.5 mM; D) glucose is increased in DBP−/− islets, despite intact responses to high (17 mM) glucose (E), shown by bar graph and traces (n = 27–29 islets, 4 animals; unpaired t test). Note that error bars (SD) are shown above (DBP−/−) and below (DBP+/+) traces so as not to obscure the mean.
(F) Expression of Pdx1, Mafa, Nkx6-1, Ins1, and Ins2 is not significantly different between DBP−/− and DBP+/+ islets (4–6 animals; paired t test).
(G–I) More δ cells are active at 5 mM glucose in DBP−/− compared to DBP+/+ islets (G and H), mounting Ca2+ spikes with a tendency toward increased amplitude (I) (representative Ca2+ images and traces are shown; images have been cropped to show a single islet; scale bar represents 40 μm; n = 28 to 29 islets, 4 animals; unpaired t test).
(J and K) Representative patch-clamp recordings of α cells (J) showing increased Na+ conductance in DBP-/- islets (K) (n = 17–22 cells, 3 animals; unpaired t test).
(L–N) Sigmoid plots of raw current data showing calculation of slope factor and half-maximal voltage (V1/2) for two cells (L). Summary data show a tendency toward increased slope factor for Na+ channel inactivation (M) but unchanged half-maximal voltage (N) in DBP−/− versus DBP+/+ α cells (n = 17–22 cells, 3 animals; Mann-Whitney test).
(O) Electrophysiological fingerprinting reveals decreased and increased probability of cells resembling an α cell or δ cell, respectively, in DBP−/− islets (n = 17–22 cells, 3 animals; Mann-Whitney test).
(P) α cell capacitance is significantly reduced in DBP−/− islets (n = 17–22 cells, 3 animals; unpaired t test).
(Q and R) Glucagon secretion is impaired in DBP−/− islets in response to low (0.5 mM) glucose and low (0.5 mM) glucose + epinephrine, shown normalized to content (Q) or fold-change (R) (n = 12–14 replicates, 10 animals; two-way ANOVA with Bonferroni’s multiple comparisons test or Mann-Whitney test).
(S) Glucagon content is similar in DBP+/+ and DBP−/− islets (n = 12 replicates, 8 animals; unpaired t test).
(T and U) Insulin secretion in response to high (17 mM) glucose or high (17 mM) glucose + KCl is increased in DBP−/− islets, shown normalized to content (T) or fold change (U) (n = 11–13 replicates, 3 animals; two-way ANOVA with Bonferroni’s multiple comparisons test or unpaired t test).
(V) Insulin content is similar in DBP+/+ and DBP−/− islets (n = 14 replicates, 3 animals; unpaired t test).
Bar graphs show scatterplot with mean ± SEM. Traces show mean ± SD. ∗p < 0.05 and ∗∗p < 0.01.