KB-R7943 Increases Glucose-Stimulated Insulin Secretion from INS-1E Cells through an NCX1-Independent Pathway

KB-R7943, a Na+/Ca+ exchanger 1 (NCX1) inhibitor, was found to enhance Glucose-Stimulated Insulin Secretion (GSIS) from human and mouse pancreatic islets through inhibiting the forward mode of NCX1. This report studied the effects of KB-R7943 and a different NCX1 inhibitor SN-6, on GSIS from INS-1E cells, a rat pancreatic beta-cell line and the potential mechanisms of action. It was found that KB-R7943 significantly enhanced GSIS from INS-1E cells in a concentration-dependent manner. In contrast, no significant effect was observed for SN-6 on GSIS. Similarly, KB-R7943 but not SN-6, enhanced glipizide, a sulfonylurea, stimulated insulin secretion from INS-1E cells. In addition, KB-R7943 but not SN-6, significantly enhanced glipizide-stimulated increase of intracellular Ca2+ ([Ca2+](i)). Transient transfection with an NCX1 siRNA resulted in 70 and 62% knockdown of NCX1 gene and protein expression, respectively, in INS-1E cells. Surprisingly, knockdown of NCX1 had little impact on KB-R7943-induced enhancement of glucose- or glipizide-stimulated insulin secretion. Similarly knockdown of NCX1 did not affect KB-R7943 mediated enhancement of glipizide-stimulated increase of [Ca2+](i). Data suggest that the enhancement effect of KB-R7943 on GSIS in INS-1E cells most likely is mediated through an NCX1-independent pathway