Inhibition of β-Cell Sodium-Calcium Exchange Enhances Glucose-Dependent Elevations in Cytoplasmic Calcium and Insulin Secretion

Abstract

OBJECTIVEThe sodium-calcium exchanger isoform 1 (NCX1) regulates cytoplasmic calcium (Ca2+c) required for insulin secretion in β-cells. NCX1 is alternatively spliced, resulting in the expression of splice variants in different tissues such as NCX1.3 and -1.7 in β-cells. As pharmacological inhibitors of NCX1 splice variants are in development, the pharmacological profile of β-cell NCX1.3 and -1.7 and the cellular effects of NCX1 inhibition were investigated.RESEARCH DESIGN AND METHODSThe patch-clamp technique was used to examine the pharmacological profile of the NCX1 inhibitor KB-R7943 on recombinant NCX1.3 and -1.7 activity. Ca2+ imaging and membrane capacitance were used to assess the effects of KB-R7943 on Ca2+c and insulin secretion in mouse and human β-cells and islets.RESULTSNCX1.3 and -1.7 calcium extrusion (forward-mode) activity was ∼16-fold more sensitive to KB-R7943 inhibition compared with cardiac NCX1.1 (IC50s = 2.9 and 2.4 vs. 43.0 μmol/l, respectively). In single mouse/human β-cells, 1 μmol/l KB-R7943 increased insulin granule exocytosis but was without effect on α-cell glucagon granule exocytosis. KB-R7943 also augmented sulfonylurea and glucose-stimulated Ca2+c levels and insulin secretion in mouse and human islets, although KB-R7943 was without effect under nonstimulated conditions.CONCLUSIONSIslet NCX1 splice variants display a markedly greater sensitivity to pharmacological inhibition than the cardiac NCX1.1 splice variant. NCX1 inhibition resulted in glucose-dependent increases in Ca2+c and insulin secretion in mouse and human islets. Thus, we identify β-cell NCX1 splice variants as targets for the development of novel glucose-sensitive insulinotropic drugs for type 2 diabetes.

Calcium Signaling in ß-cell Physiology and Pathology: A Revisit

“…Notably, the activity of the forward-mode (i.e., 1Ca 2+ out/3Na + in) of the NCX in the pancreatic β-beta-cell is sensitive to long-chain acyl-coenzyme and alterations in intracellular acyl-CoA levels may cause negatively control Ca 2+ -mediated exocytosis and insulin secretion [108]. Moreover, the forward mode of the NCX1 splice variants of that is expressed in the pancreatic β-cells (NCX1.3 and NCX1.7) exhibit an unusually high sensitivity to KB-R7943 [109] that rather selectively inhibits the reversed mode of the NCX (i.e., 1Ca 2+ in/3Na + out) in most other cell types. Consequently, the pharmacological inhibition of the NCX1 with KB-R7943 results in a considerable augmentation in glucose-stimulated increases in cytosolic Ca 2+ concentrations and insulin secretion in mouse and human β-cell islets, while KB-R7943 was without effect under non-stimulated conditions.…”

Local and regional control of calcium dynamics in the pancreatic islet

“…While their contribution compared with the ER is small, membrane exchangers and pumps still play an important role in Ca 2+ homeostasis in the β‐cell. Recent studies have shown that inhibition of the sodium‐calcium exchanger isoform 1 (NCX1) results in glucose‐dependent increases in cytosolic Ca 2+ concentration and insulin secretion . Similarly, heterozygous inactivation of the plasma membrane Ca 2+ ATPase (PMCA) leads to intracellular Ca 2+ accumulation, augmented insulin release and, strikingly, improved β‐cell proliferation, viability and mass …”

2-Aminoadipic acid is a biomarker for diabetes risk

“…We also performed studies in murine islets isolated from male C57BL/6J mice as previously reported (27). Islets were obtained by collagenase digestion of the pancreas, purified by Ficoll density gradient, handpicked, and then cultured for 24 hours.…”