Ca2+ influx through L-type Ca2+ channels and Ca2+-induced Ca2+ release regulate cAMP accumulation and Epacl-dependent ERK 1/2 activation in INS-1 cells

We previously reported that INS-1 cells expressing the intracellular II-Ill loop of the L-type Cat} channel Ca(v)1.2 (Ca(v)1.2/II-III cells) are deficient in Ca2+-induced Ca2+ release (CICR). Here we show that glucose stimulated ERR 1/2 phosphorylation (GSEP) is slowed and reduced in Ca(v)1.2/II-III cells compared to INS-1 cells. This parallels a decrease in glucose-stimulated cAMP accumulation (GS-cAMP) in Ca(v)1.2/II-III cells. Influx of Ca2+ via L-type Ca2+ channels and CICR play roles in both GSEP and GS-cAMP in INS-1 cells since both are inhibited by nicardipine or ryanodine. Further, the Epac1-selective inhibitor CE3F4 abolishes glucose-stimulated ERR activation in INS-1 cells, as measured using the FRET-based sensor EKAR. The non-selective Epac antagonist ESI-09 but not the Epac2-selective antagonist ESI-05 nor the PICA antagonist Rp-cAMPs inhibits GSEP in both INS-1 and Ca(v)1.2/II-III cells. We conclude that L-type Ca2+ channel dependent cAMP accumulation, that's amplified by CICR, activates Epac1 and drives GSEP in INS-1 cells. (C) 2015 Elsevier Ireland Ltd. All rights reserved.