The Intracellular II-III Loops of Cav1.2 and Cav1.3 Uncouple L-Type Voltage-Gated Ca2+ Channels from Glucagon-Like Peptide-1 Potentiation of Insulin Secretion in INS-1 Cells via Displacement from Lipid Rafts

Abstract

L-type Ca 2ϩ channels play a key role in the integration of physiological signals regulating insulin secretion that probably requires their localization to specific subdomains of the plasma membrane. We investigated the role of the intracellular II-III loop domains of the L-type channels Ca v 1.2 and 1.

An Improved Targeted cAMP Sensor to Study the Regulation of Adenylyl Cyclase 8 by Ca2+ Entry through Voltage-Gated Channels

“…Pancreatic β-cells express both Ca v 1.2 and Ca v 1.3 channels [43,48], which contain the α1C and α1D subunits respectively. Overexpression of GFP-α1C and GFP-α1D in HEK293 cells produced bands of expected size on a Western blot (Figure 5A).…”

Cav1.2 and Cav1.3 Are Differentially Coupled to Glucagon-Like Peptide-1 Potentiation of Glucose-Stimulated Insulin Secretion in the Pancreatic β-Cell Line INS-1

“…2C, 50 nM GLP-1 robustly potentiated 7.5 mM GSIS in Ca v 1.3/DHPi cells, to an extent similar to untransfected INS-1 cells. In contrast to both untransfected INS-1 cells and Ca v 1.2/DHPi cells, 10 M nifedipine did not significantly block insulin secretion in response to 7.5 mM glucose ϩ 50 nM GLP-1 in (Jacobo et al, 2009), and cell-permeable analogs of cAMP can potentiate GSIS in INS-1 cells (Liu et al, 2006). Therefore, we examined the effect of the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX; 100 M) on 50 nM GLP-1 potentiation of 7.5 mM GSIS in INS-1 cells, and Ca v 1.2/DHPi, and Ca v 1.3/DHPi cells in the presence of 10 M nifedipine (Fig.…”

“…Biochemical evidence also supports the specific relationship between EPAC2 and Ca v 1.2. The intracellular loop between homologous domains II and III of Ca v 1.2, but not Ca v 1.3, binds to the scaffolding proteins Rab3-interacting molecule 2 (RIM2) and Piccolo in vitro (Shibasaki et al, 2004), and immunoprecipitates full-length RIM2 from INS-1 cells (Jacobo et al, 2009). RIM2 and Piccolo are both involved in EPAC2 mediated, cAMP-dependent potentiation of GSIS (Fujimoto et al, 2002).…”

Molecular physiology of glucagon-like peptide-1 insulin secretagogue action in pancreatic β cells

“…Both Piccolo and Rim2 are reported to bind to the α1.2 subunit of L-type Ca 2+ channels in β cells (Shibasaki et al, 2004a), and this interaction may anchor L-type Ca 2+ channels in lipid rafts to form a signaling complex important for glucose and GLP-1 regulated insulin secretion (Jacobo et al, 2009b). The intracellular II-III loop of Ca V 1.2 immunoprecipitates with Rim2 (Jacobo et al, 2009b), consistent with previous data showing that Rim2 specifically binds Ca V 1.2 through its C2 domain (Shibasaki et al, 2004a). These findings correlate with the fact that that the knockdown of Ca V 1.2 expression in INS-1 cells disrupts GSIS (Nitert et al, 2008).…”