Linoleic Acid Stimulates [Ca2+]i Increase in Rat Pancreatic Beta-Cells through Both Membrane Receptor- and Intracellular Metabolite-Mediated Pathways

The role of the free fatty acid (FFA) receptor and the intracellular metabolites of linoleic acid (LA) in LA-stimulated increase in cytosolic free calcium concentration ([Ca2+]i) was investigated. [Ca2+]i was measured using Fura-2 as indicator in rat pancreatic beta-cells in primary culture. LA (20 mu M for 2 min) stimulated a transient peak increase followed by a minor plateau increase in [Ca2+]i. Elongation of LA stimulation up to 10 min induced a strong and long-lasting elevation in [Ca2+]i. Activation of FFA receptors by the non-metabolic agonist GW9508 (40 mu M for 10 min) resulted in an increase in [Ca2+]i similar to that of 2-min LA treatment. Inhibition of acyl-CoA synthetases by Triacsin C suppressed the strong and long-lasting increase in [Ca2+]i. The increase in [Ca2+]i induced by 2 min LA or GW9508 were fully eliminated by exhaustion of endoplasmic reticulum (ER) Ca2+ stores or by inhibition of phospholipase C (PLC). Removal of extracellular Ca2+ did not influence the transient peak increase in [Ca2+]i stimulated by 2 min LA or GW9508. The strong and long-lasting increase in [Ca2+]i induced by 10 min LA was only partially suppressed by extracellular Ca2+ removal or thapsigargin pretreatment, whereas remaining elevation in [Ca2+]i was eliminated after exhaustion of mitochondrial Ca2+ using triphenyltin. In conclusion, LA stimulates Ca2+ release from ER through activation of the FFA receptor coupled to PLC and mobilizes mitochondrial Ca2+ by intracellular metabolites in b-cells.