First-phase insulin secretion in vivo and ex vivo. A: Mean time course of plasma insulin levels from Cx36+/+ (■) and Cx36−/− mice (◇) before and immediately after glucose infusion, as well as between 45 and 55 min after glucose infusion. Sampling
rate is one per minute. n = 5 littermate mice in each group. B: Mean time course of insulin secretion levels from isolated Cx36+/+ and Cx36−/− islets (per 100 IEQ) after elevated glucose levels. Arrow indicates glucose step from 2.8 to 11.1 mM. Sampling rate is 0.5
per minute until t = 20, then 0.25 per minute thereafter. n = 6 sets of islets from individual mice in each group. *, significant reduction; †, significant elevation (P < 0.05, paired Student t test) in Cx36−/− islets compared with Cx36+/+ islets. C: Summary of mean plasma insulin levels prior to glucose infusion (basal), peak plasma insulin levels 1–3 min after glucose
infusion (first phase), and mean plasma insulin levels 45–55 min after glucose infusion (second phase). D: Summary of mean insulin secretion levels during perifusion, prior to glucose elevation (basal), peak insulin secretion at
10 min after glucose elevation (first phase), and mean insulin secretion 40 min after glucose elevation (second phase). E: Mean time from first-phase peak of insulin secretion to first minimum of insulin secretion. F: Mean time-integrated insulin secretion from initial elevation at t = 5 min to first minimum of insulin secretion between t = 10 and 20 min. *, significant difference (P < 0.05, Student t test); NS, no significant difference (P > 0.1, Student t test), comparing each measurement in Cx36+/+ and Cx36−/− mice or islets.