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To elucidate GPR40/FFA 1 and its downstream signaling pathways in regulating insulin secretion.Methods GPR40/FFA 1 expression was detected by immunofluorescence imaging.We employed linoleic acid (LA),a free fatty acid that has a high affinity to the rat GPR40,and examined its effect on cytosolic free calcium concentration ([Ca2+]i) in primary rat β-cells by Fluo-3 intensity under confocal microscopy recording.Downregulation of GPR40/FFA1 expression by antisense oligonucleotides was performed in pancreatic β-cells,and insulin secretion was assessed by enzyme-linked immunosorbent assay.Results LA acutely stimulated insulin secretion from primary cultured rat pancreatic islets.LA induced significant increase of [Ca2+]i in the presence of 5.6 mmol/L and 11.1 mmol/L glucose,which was reflected by increased Fluo-3 intensity under confocal microscopy recording.LA-stimulated increase in [Ca2+]i and insulin secretion were blocked by inhibition of GPR40/FFA1 expression in β-cells after GPR40/FFA1-specific antisense treatment.In addition,the inhibition of phospholipase C (PLC) activity by U73122,PLC inhibitor,also markedly inhibited the LA-induced [Ca2+]i increase.Conclusion LA activates GPR40/FFA1 and PLC to stimulate Ca2+ release,resulting in an increase in [Ca2+]i and insulin secretion in rat islet β-cells.