title: Reduction in voltage-gated K+ currents in primary cultured rat pancreatic beta-cells by linoleic acids.
abstract: Free fatty acids (FFAs), in addition to glucose, have been shown to stimulate insulin release through the G protein-coupled receptor (GPCR)40 receptor in pancreatic beta-cells. Intracellular free calcium concentration ([Ca(2+)](i)) in beta-cells is elevated by FFAs, although the mechanism underlying the [Ca(2+)](i) increase is still unknown. In this study, we investigated the action of linoleic acid on voltage-gated K(+) currents. Nystatin-perforated recordings were performed on identified rat beta-cells. In the presence of nifedipine, tetrodotoxin, and tolbutamide, voltage-gated K(+) currents were observed. The transient current represents less than 5%, whereas the delayed rectifier current comprises more than 95%, of the total K(+) currents. A long-chain unsaturated FFA, linoleic acid (10 microm), reversibly decreased the amplitude of K(+) currents (to less than 10%). This reduction was abolished by the cAMP/protein kinase A system inhibitors H89 (1 microm) and Rp-cAMP (10 microm) but was not affected by protein kinase C inhibitor. In addition, forskolin and 8'-bromo-cAMP induced a similar reduction in the K(+) current as that evoked by linoleic acid. Insulin secretion and cAMP accumulation in beta-cells were also increased by linoleic acid. Methyl linoleate, which has a similar structure to linoleic acid but no binding affinity to GPR40, did not change K(+) currents. Treatment of cultured cells with GPR40-specific small interfering RNA significantly reduced the decrease in K(+) current induced by linoleic acid, whereas the cAMP-induced reduction of K(+) current was not affected. We conclude that linoleic acid reduces the voltage-gated K(+) current in rat beta-cells through GPR40 and the cAMP-protein kinase A system, leading to an increase in [Ca(2+)](i) and insulin secretion.
authors.affiliation: Prince Henry's Institute of Medical Research, Clayton, Victoria, Australia. chen.chen@princehenrys.org
authors.forename: Dan Dan
authors.initials: DD
authors.lastname: Feng
authors.forename: Ziqiang
authors.initials: Z
authors.lastname: Luo
authors.forename: Sang-Gun
authors.initials: SG
authors.lastname: Roh
authors.forename: Maria
authors.initials: M
authors.lastname: Hernandez
authors.forename: Neveen
authors.initials: N
authors.lastname: Tawadros
authors.forename: Damien J
authors.initials: DJ
authors.lastname: Keating
authors.forename: Chen
authors.initials: C
authors.lastname: Chen
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D019787:Linoleic Acid / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: C473035:G-protein-coupled receptor 40, rat; D007328:Insulin; D024642:Potassium Channels, Voltage-Gated; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D019787:Linoleic Acid; D017868:Cyclic AMP-Dependent Protein Kinases