![PKA- and Epac2-dependent effects of glucose and forskolin on depolarization-induced somatostatin secretion by ER Ca2+ release. PKA- and Epac2-dependent intracellular Ca2+ release is involved in somatostatin secretion in depolarized δ-cells—an effect that is independent of membrane depolarization. (A) Somatostatin secretion in response to 1 mM and 20 mM glucose in islets depolarized with 70 mM [K+]o under control conditions and in the presence of PKI (1 µM), ESI-05 (25 µM), or both blockers, as indicated. ***, P < 0.001 vs. 1 mM glucose under same condition; ††, P < 0.01 and †††, P < 0.001 vs. 20 mM glucose alone. (B) Somatostatin secretion measured in the absence and presence of 2 µM forskolin (at 1 mM glucose) in islets depolarized with 70 mM [K+]o. Effect of PKI (1 µM), ESI-05 (25 µM), or simultaneous application of both blockers on forskolin-stimulated somatostatin secretion was tested. *, P < 0.05 and ***, P < 0.001 vs. somatostatin secretion under control condition; †††, P < 0.001 vs. somatostatin in the presence of 2 µM forskolin alone. (C) As in B but testing the effect of preincubation with thapsigargin (10 µM, 1 h) on 2 µM forskolin-stimulated somatostatin secretion (triggered by 70 mM [K+]o). ***, P < 0.001 vs. somatostatin secretion under the control condition; †††, P < 0.001 vs. somatostatin secretion in the presence of 2 µM forskolin alone. (D) Somatostatin secretion in response to 1 mM and 20 mM glucose in islets depolarized with 70 mM [K+]o under control condition and in the presence of ryanodine, PKI or ESI-05 as indicated. *, P < 0.05; **, P < 0.01; and ***, P < 0.001 vs. 1 mM glucose alone; †††, P < 0.001 vs. 20 mM glucose alone. (E) 70 mM [K+]o-triggered somatostatin secretion measured in the absence and presence of forskolin (2 µM), Sp-8-Br-cAMP (100 µM), or Epac2 agonist (S-223, 100 µM). ESI-05 (25 µM) was applied in the presence of Sp-8-Br-cAMP or S-223 to test the specificity of the agonists. ***, P < 0.001 vs. somatostatin secretion under the control condition; †††, P < 0.001 vs. somatostatin secretion in the presence of 100 µM Sp-8-Br-cAMP alone; and ‡‡‡, P < 0.001 vs. somatostatin secretion in the presence of 100 µM S-223 alone. In A–E, data are presented as mean values ± SEM for the indicated numbers of independent experiments (n). Islets from more than three animals were used for each experiment.](https://cdn.rupress.org/rup/content_public/journal/jgp/151/9/10.1085_jgp.201912351/10/jgp_201912351_fig4.jpeg?Expires=1767786881&Signature=01BXPI~3dIzvf716Lfm4AVPVSVLtOioqZX9rysRG50CZ9LRgdj~S6wgx3xwdkuNbt6dN89qro9P25qM17fWdH4oe63zGDsRMY139TPXOpejXR8wWN4zofiDwyX~WjEN4Z1IxK-BY55xi4gvvOlONzQfS2i4YGKlwJXWf4zTGUPCO2dfP9WDvKDAF-3wSF0L1S8RCw3tfWlmckUrQ5k7uvOn6pOMtNe8ypl~J0v1C8lMOBYgdeM5-fdhQdEkGa0d3mv-NDG94rNLPxpW46Bb~NFFz~S02bek6MPye2X1axnFfB6b8L1nCb~KNO-UdaPozKaZ1UVY0GlSFpWMNvonhYw__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
PKA- and Epac2-dependent effects of glucose and forskolin on depolarization-induced somatostatin secretion by ER Ca2+ release. PKA- and Epac2-dependent intracellular Ca2+ release is involved in somatostatin secretion in depolarized δ-cells—an effect that is independent of membrane depolarization. (A) Somatostatin secretion in response to 1 mM and 20 mM glucose in islets depolarized with 70 mM [K+]o under control conditions and in the presence of PKI (1 µM), ESI-05 (25 µM), or both blockers, as indicated. ***, P < 0.001 vs. 1 mM glucose under same condition; ††, P < 0.01 and †††, P < 0.001 vs. 20 mM glucose alone. (B) Somatostatin secretion measured in the absence and presence of 2 µM forskolin (at 1 mM glucose) in islets depolarized with 70 mM [K+]o. Effect of PKI (1 µM), ESI-05 (25 µM), or simultaneous application of both blockers on forskolin-stimulated somatostatin secretion was tested. *, P < 0.05 and ***, P < 0.001 vs. somatostatin secretion under control condition; †††, P < 0.001 vs. somatostatin in the presence of 2 µM forskolin alone. (C) As in B but testing the effect of preincubation with thapsigargin (10 µM, 1 h) on 2 µM forskolin-stimulated somatostatin secretion (triggered by 70 mM [K+]o). ***, P < 0.001 vs. somatostatin secretion under the control condition; †††, P < 0.001 vs. somatostatin secretion in the presence of 2 µM forskolin alone. (D) Somatostatin secretion in response to 1 mM and 20 mM glucose in islets depolarized with 70 mM [K+]o under control condition and in the presence of ryanodine, PKI or ESI-05 as indicated. *, P < 0.05; **, P < 0.01; and ***, P < 0.001 vs. 1 mM glucose alone; †††, P < 0.001 vs. 20 mM glucose alone. (E) 70 mM [K+]o-triggered somatostatin secretion measured in the absence and presence of forskolin (2 µM), Sp-8-Br-cAMP (100 µM), or Epac2 agonist (S-223, 100 µM). ESI-05 (25 µM) was applied in the presence of Sp-8-Br-cAMP or S-223 to test the specificity of the agonists. ***, P < 0.001 vs. somatostatin secretion under the control condition; †††, P < 0.001 vs. somatostatin secretion in the presence of 100 µM Sp-8-Br-cAMP alone; and ‡‡‡, P < 0.001 vs. somatostatin secretion in the presence of 100 µM S-223 alone. In A–E, data are presented as mean values ± SEM for the indicated numbers of independent experiments (n). Islets from more than three animals were used for each experiment.
