Release of a peptide co-transmitter from INS-1 beta cells is potentiated by cAMP.

<p>(A). Example of secretory events recorded from a transfected INS-1 cell before and after the application of 5 µM forskolin. The number of secretory events are indicated by the filled symbols to the right of the records. Shown are sections of 5 consecutive traces before (sweeps 1–5) and 5 consecutive traces after (sweeps 58–62) the application of forskolin. (B). Example experiment showing the time course of the potentiating effect of 5 µM forskolin on peptide secretion (open circles; same cell as in A). Square symbols show the amplitude of the depolarization-evoked calcium current over the course of the experiment. (C). Group data showing the effect of forskolin (n = 8 cells). The effect was quantified by comparing the gradient of the time-cumulative event amplitude relationship before and after the addition of 1–5 µM forskolin (n = 8 cells; mean ± SD; P<0.05, paired one-tailed t test). Cells in (A–C) were stimulated using the perforated patch technique at 0.1 or 1 Hz with a 20 ms depolarizing step from −80 to +20 mV. (D). Inclusion of 100 µM N⁶-benzoyl-cAMP, a selective activator of PKA, in the whole cell patch pipette solution significantly potentiated peptide secretion (n = 8 cells, mean ± SD; P<0.05, Mann-Whitney test). (E). Inclusion of 100 µM 2′-O-Me-cAMP, an EPAC activator, in the pipette solution did not significantly increase peptide secretion (n = 6 cells, mean ± SD; P<0.05, Mann-Whitney test). Cells in D and E were stimulated as described (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0019478#pone-0019478-g004" target="_blank">Figure 4C</a>).