PT - JOURNAL ARTICLE AU - Guohong Liu AU - Sarah Melissa P. Jacobo AU - Nathan Hilliard AU - Gregory H. Hockerman TI - Differential Modulation of Ca<sub>v</sub>1.2 and Ca<sub>v</sub>1.3-Mediated Glucose-Stimulated Insulin Secretion by cAMP in INS-1 Cells: Distinct Roles for Exchange Protein Directly Activated by cAMP 2 (Epac2) and Protein Kinase A AID - 10.1124/jpet.105.097477 DP - 2006 Jul 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 152--160 VI - 318 IP - 1 4099 - http://jpet.aspetjournals.org/content/318/1/152.short 4100 - http://jpet.aspetjournals.org/content/318/1/152.full SO - J Pharmacol Exp Ther2006 Jul 01; 318 AB - Using insulin-secreting cell line (INS)-1 cells stably expressing dihydropyridine-insensitive mutants of either Cav1.2 or Cav1.3, we previously demonstrated that Cav1.3 is preferentially coupled to insulin secretion and [Ca2+]i oscillations stimulated by 11.2 mM glucose. Using the same system, we found that insulin secretion in 7.5 mM glucose plus 1 mM 8-bromo-cAMP (8-Br-cAMP) is mediated by both Cav1.2 and Cav1.3. Treatment of INS-1 cells or INS-1 cells stably expressing Cav1.2/dihydropyridine-insensitive (DHPi) channels in the presence of 10 μM nifedipine, with effector-specific cAMP analogs 8-(4-chlorophenylthio)-2′-O-methyladenosine-cAMP [8-pCPT-2′-O-Me-cAMP; 100 μM; Exchange Protein directly Activated by cAMP 2 (Epac2)-selective] or N6-benzoyl-cAMP [50 μM; Protein Kinase A (PKA)-selective] partially increased insulin secretion. Secretion stimulated by a combination of the two cAMP analogs was additive and comparable with that stimulated by 1 mM 8-Br-cAMP. In INS-1 cells stably expressing Cav1.3/DHPi in the presence of 10 μM nifedipine, N6-benzoyl-cAMP, but not 8-pCPT-2′-O-Me-cAMP, significantly increased glucose-stimulated insulin secretion. However, the combination of N6-benzoyl-cAMP and 8-pCPT-2′-O-Me-cAMP significantly increased glucose-stimulated secretion compared with N6-benzoyl-cAMP alone. In INS-1 cells, 8-Br-cAMP potentiation of insulin secretion in 7.5 mM glucose is blocked by thapsigargin (1 μM) and ryanodine (0.5 μM). In contrast, ryanodine has no effect on insulin secretion or [Ca2+]i oscillations stimulated by 11.2 mM glucose in INS-1 cells. Our data suggest that both Cav1.2 and Cav1.3 mediate insulin secretion stimulated by 7.5 mM glucose and cAMP via a mechanism that requires internal stores of Ca2+. Furthermore, cAMP modulation of secretion mediated by Cav1.2 seems to involve both Epac2 and PKA independently. In contrast, cAMP modulation of Cav1.3-mediated secretion depends upon PKA activation, whereas the contribution of Epac2 is dependent upon PKA activation. The American Society for Pharmacology and Experimental Therapeutics