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 β-cells in primary culture. LA (20 µM 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 µM 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 β-cells.