A, upper trace: continuous recording of [Ca2+]i (F340/F380 fluorescence ratio) from a single fura-2/5-HT-loaded islet; lower trace: continuous recording of 5-HT/insulin release (amperometric current) from the same islet. Glucose concentration was stepped from 11 to 20 mM (bar). B, analysis of the glucose dependence of pulsatile 5-HT/insulin release, in terms of the time integral of the current response for each cycle (in pC, left) and oscillation frequency (right). Both parameters were assessed at the steady state of 11 and 20 mM glucose (data from four experiments including that depicted in A, represented by circles). Each point represents the mean value ± s.e.m. (n = 6 cycles). Statistical significance of differences was assessed by Student's t test (* P < 0.05; ** P < 0.001). C, correlation between the integrated current response per cycle and the duration (time from half-rise to half-decay) of the underlying [Ca2+]i oscillation. Both parameters were assessed at the steady state of 11 and 20 mM glucose. Pooled non-normalized data from four experiments (open and filled symbols for 11 and 20 mM glucose, respectively). The straight line was drawn by least squares fitting to the whole data (slope, 0.97 pC s−1; correlation coefficient, 0.93). D, maximal amplitude of the [Ca2+]i oscillations as a function of glucose concentration. Δ (F340 /F380) was assessed at the steady state of 11 and 20 mM glucose (data from the same experiments used to generate the data in B). Each point represents the mean value ± s.e.m., for n = 6 cycles (the differences within each experiment were not statistically significant by Student's t test, P > 0.05).