ObjectiveTo elucidate GPR40/FFA1 and its downstream signaling pathways in regulating insulin secretion. Methods GPR40/FFA1 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 ([Ca

2+

]

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 [Ca

2+

]

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

[Ca

2+

]

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 [Ca

2+

]

i

increase. Conclusion LA activates GPR40/FFA1 and PLC to stimulate Ca

2+

release

resulting in an increase in [Ca2+]

i

and insulin secretion in rat islet β-cells.