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1 Prince Henry's Institute of Medical Research, PO Box 5152, Clayton, Victoria 3168, Australia2 Department of Physiology, Fourth Military Medical University, Xi'an 710032, China3 School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
(Correspondence should be addressed to C Chen; Email: chen.chen{at}uq.edu.au)
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionDeclaration of interestReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of interestReferences |
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The pancreatic β-cell is excitatory and exhibits depolarization of membrane potential (MP) and bursting of action potentials when stimulated by glucose (Rorsman 1997). MP is very important to insulin secretion because it determines the opening and closure of voltage-dependent calcium channels and other voltage-dependent channels. There is evidence that linoleic acid (LA) influences the action of voltage-dependent potassium channels on the membrane of rat pancreatic β-cells via GPR40 and the cAMP and protein kinase A (PKA) intracellular signalling system (Feng et al. 2006). In addition, it is found that LA inhibits voltage-dependent calcium channels via calcium-dependent inactivation pathway in rat β-cells (Feng et al. 2008). However, the effects of LA on MP and KATP channel activity are not clarified. In this study, we first observed the effects of LA on MP. Surprisingly, we found that LA strongly hyperpolarizes MP of rat pancreatic β-cells by activating KATP channels. Both the intracellular metabolic pathway and the GPR40 receptor pathway are involved in the effects of LA on KATP channels.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of interestReferences |
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LA was purchased from Sigma. GW9508 was obtained from GlaxoSmithKline. Histopaque-1077, dispase, collagenase (type V), DNase I, BSA, Roswell Park Memorial Institute (RPMI) 1640 medium, tolbutamide and all reagents for bath solution and pipette solutions were purchased from Sigma. H89 and chelerythrine was from Calbiochem (San Diego, CA, USA). Fetal calf serum, HEPES and penicillin/streptomycin were obtained from Thermo Electron (Melbourne, Australia).
Preparation and culture of rat pancreatic β-cells
Pancreatic islets were isolated from 10- to 12-week-old male Sprague–Dawley rats as described previously (Zhao et al. 2003). The rats were obtained from the Monash University and killed by CO2 inhalation as approved by the Animal Ethics Committee of Monash University. The pancreas was inflated by injecting 10 ml collagenase solution into it through the bile duct. The collagenase solution was composed of 0.5 mg/ml collagenase, 0.1 mg/ml DNase I and 1 mg/ml BSA in Hank's balanced salt solution (HBSS). The pancreas was collected and digested at 37 °C for 30 min in a stationary state, and then dispersed by shaking. The islets were separated from the pancreas by Histopaque-1077 density gradient centrifugation and collected under microscope. The islets were dispersed into single cells by digestion with dispase solution (1 mg/ml dispase, 0.1 mg/ml DNase I and 1 mg/ml BSA in Ca2+-free HBSS). The islet cells were plated onto 35 mm Petri dishes and cultured in RPMI 1640 medium at 8 mM glucose supplemented with 10% heat-inactivated fetal calf serum, 100 IU/ml penicillin and 100 g/ml streptomycin in a humidified atmosphere of 95% air and 5% CO2. The culture medium was changed every 2 days. The experiments were performed during days 3–6 in culture.
Electrophysiological recording
Cells were washed and kept in bath solution before recording. The recordings were made under perforated whole-cell patch-clamp configuration. Electrodes were pulled by a Sutter P-87 microelectrode puller from borosilicate micropipettes and had an initial input resistance of 3–5 M
. All recordings were performed using the Axopatch 200A amplifier (Axon Instrument, Union City, CA, USA). The bath solution for MP and KATP current recordings was composed of (mM): 140 NaCl, 4.7 KCl, 2.6 CaCl2, 1.2 MgSO4, 1 NaHCO3, 1.2 Na2HPO4, 5 glucose and 5 HEPES (pH 7.4 with NaOH). The pipette solution for the recording was composed of (mM): 76 K2SO4, 10 KCl, 10 NaCl, 8 MgSO4, 20 HEPES (pH 7.3 with NaOH). After the formation of a high-resistance seal, the voltage in the pipette was held at –80 mV. Membrane perforation was achieved by 0.24 mg/ml nystatin in the pipette solution, and a series resistance decreasing to lower than 30 M was considered indicative of sufficient access to the cell interior. The whole-cell capacitance and series resistance were well compensated. MP or KATP current was recorded using different protocols. MP was recorded under current-clamp mode using AxoScope 8 program, as the current was held at 0 pA. KATP current was recorded under voltage-clamp mode using Clampex 8 program. The cells were held at –80 mV, and a trial of sweeps was obtained by clamping from –110 to –50 mV at intervals of 1 s, with 20 mV increments and 300 ms duration of each step. Drugs were given through a perfusion system at 3 ml/min. β-Cells were identified by cell size and cell membrane capacitance. The mean capacitances of β- and 
-cells are 5.5±0.3 and 2.8±0.1 pF respectively (Gopel et al. 2000, Leung et al. 2005). For the current experiment, β-cell measurements were limited to cells whose whole-cell capacitance, after clamping, equalled to or exceeded 6 pF. Experiments were performed at room temperature.
Statistical analysis
Data are presented as mean±S.E.M. for each group. One-way ANOVA was used to analyse the statistical significance between different groups. P<0.05 was taken as the minimum level of significance.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of interestReferences |
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Rat pancreatic β-cells had a MP between –60 and –40 mV at 5 mM glucose condition. MP remained stable during 20 min recording in control. LA induced a quick hyperpolarization of MP. The MP of the control was –48.33±3.964 mV and became hyperpolarized to –76.25±1.962 mV when 20 µM LA was added (P<0.01, n=12). LA instantly induced hyperpolarization and the time to reach the stable level was 4.199±0.562 min (n=12). After washout of LA, the MP had a slow partial recovery, and 8.547±2.041 min elapsed before 50% recovery was reached (Fig. 1A and B). Glucose (15 mM) stimulated depolarization of β-cells, and in the presence of glucose, LA induced hyperpolarization of β-cells (–40.69±5.062 mV at 15 mM glucose and –73.58±4.531 mV with LA, P<0.01, n=6; Fig. 1C and D).
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The blockade of LA-induced hyperpolarization by tolbutamide, a specific blocker of KATP channels, indicated that activation of KATP channels is responsible for the LA-induced hyperpolarization. In 5 mM glucose, there was a small KATP current. LA induced an increased opening of KATP channels. Ten minutes after LA incubation, the KATP currents reached maximal levels. The I–V curve shows that KATP currents were significantly increased at each clamping step. KATP currents increased from –2.052±0.273 pA/pF to –24.621±3.818 pA/pF at –110 mV (P<0.01, n=12; Fig. 3A). With the addition of 0.1 mM tolbutamide, LA could not induce the opening of KATP channels (Fig. 3B).
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LA can get into β-cells by flip-flop across the plasma membrane and metabolized to generate acyl-CoA, and it was found that acyl-CoA can induce opening of KATP channels (Larsson et al. 1996, Branstrom et al. 2004). We next tested the effects of blockade of acyl-CoA formation by inhibiting acyl-CoA synthetase using triacsin C. Triacsin C (10 µM) itself did not influence KATP currents after 10-min incubation. In the presence of triacsin C, LA could induce opening of KATP channels (Fig. 4A). However, the maximal levels of KATP currents were significantly reduced by triacsin C treatment. The change in the currents from –110 to –50 mV was significantly reduced in the group with triacsin C treatment (19.09±4.403 in control versus 6.950±2.240 in triacsin C treatment, P<0.05, n=6; Fig. 4B).
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The partial inhibition of LA-induced activation of KATP channels by triacsin C indicates that non-metabolic pathways such as the GPR40 receptor pathway may take part in the action of LA on KATP channels. Since use of LA could not exclude the involvement of metabolic pathways, we used GW9508, a small-molecule non-metabolic agonist of GPR40, to test whether GPR40 activation contributes to LA-induced opening of KATP channels. GW9508 induced hyperpolarization and opening of KATP channels in rat β-cells. As shown in Fig. 5A, GW9508 at 40 µM hyperpolarized the MP of rat β-cells from –48.25±2.477 to –66.50±1.812 mV (P<0.01, n=8). Tolbutamide totally blocked the hyperpolarization induced by GW9508 (–28.14±3.203 mV versus –30.01±1.543 mV, P>0.5, n=7). In contrast to LA-induced hyperpolarization, the hyperpolarization induced by GW9508 recovered fully and quickly in 5 min after washout of GW9508. According to the hyperpolarization, GW9508 induced opening of KATP channels. It increased the KATP currents from –2.691±0.478 to –11.056±1.599 pA/pF at –110 mV (P<0.01, n=8). However, the KATP currents induced by GW9508 were significantly smaller than that induced by LA (–11.056±1.599 pA/pF at –110 mV for GW9508, n=8; –24.621±3.818 pA/pF at –110 mV for LA, n=12, P<0.01). The opening of KATP channels induced by GW9508 was totally reversed by tolbutamide in 5 min (Fig. 5B). To exclude the possibility of non-receptor-mediated effects of GW9508 on KATP channels, we observed the effects of GW9508 on KATP channels in GH3 cells, a growth hormone (GH)-secreting cell line that does not express GPR40 as identified by reverse transcription PCR (Yang et al. 2005, Feng et al. 2006). GW9508 at 40 µM did not increase the KATP channels in GH3 cells (–1.587±0.208 pA/PF in control and –1.641±0.249 pA/pF after GW9508, no significant difference, n=5).
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We next tested whether protein kinases A and C (PKA and PKC) signalling pathways mediate the effects of LA on KATP channels. PKA inhibitor, 1 µM H89, did not influence KATP channels. After treatment with H89 for 10 min, LA induced opening of KATP channels, and we observed no difference in the amplitude at each clamping step. PKC inhibitor, 10 µM chelerythrine, neither influenced KATP channels by itself nor influenced LA-induced opening of KATP channels. In addition, H89 and chelerythrine did not influence GW9508-induced opening of KATP channels. The amplitude of KATP currents at –110 mV is shown in Fig. 6.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of interestReferences |
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First, we showed that activation of KATP channels is responsible for LA-induced hyperpolarization in rat β-cells. Pancreatic KATP channels are formed by two different types of subunits, the Kir6.2 inwards rectifying potassium channels and sulphonylurea receptor subunit SUR1 (Mikhailov & Ashcroft 2000, Mikhailov et al. 2000). Pancreatic KATP channels can be specifically blocked by sulphonylurea such as tolbutamide (Ashfield et al. 1999, Gribble & Ashcroft 2000). LA-induced hyperpolarization was reversed by tolbutamide and was deterred by tolbutamide pretreatment, indicating that opening of KATP channels is responsible for the hyperpolarization. This was confirmed by the current recording. LA induced strong non-voltage-dependent currents that were totally blocked by tolbutamide, confirming that LA opened KATP channels. KATP channels play an important role in the process of GSIS. Glucose goes to aerobic oxidation to produce ATP from ADP in β-cells. The resulting increase in the ATP/ADP ratio closes KATP channels and leads to depolarization of MP and subsequent activation of voltage-gated Ca2+ channels (Ca2+(v) channels). The influx of Ca2+ results in an increase in intracellular Ca2+ concentration ([Ca2+]i), which triggers exocytosis of insulin granules (Rorsman 1997). Activation of KATP channels results in a decrease in the excitability of β-cells and inhibits insulin secretion. Although FFAs stimulate insulin secretion, FFAs substantially inhibits GSIS in a long-term condition (Zraika et al. 2002, Haber et al. 2003). LA-induced activation of KATP channels may play a role in decreasing β-cell glucose sensitivity and be the reason for the inhibition of GSIS by FFAs. The stimulatory effects of FFAs on insulin secretion should be due to the KATP channel-independent pathway. For example, FFAs stimulate calcium release from intracellular calcium stores via GPR40 membrane receptor and then trigger insulin secretion. Moreover, FFAs metabolites such as long-chain acyl-CoA activate PKC that facilitates insulin secretion in the distal step of exocytosis. Long-chain acyl-CoA may involve acylation of exocytosis-related proteins and facilitate the exocytosis of secretory granules of insulin (Hess et al. 1992, Braun & Scheller 1995).
The mechanism of activation of KATP channels was not previously fully understood. It was suggested that long-chain acyl-CoA activates KATP channels (Larsson et al. 1996, Branstrom et al. 2004, Manning Fox et al. 2004). Single-channel recording has shown that long-chain acyl-CoA esters induce a rapid, strong and slowly reversible opening of KATP channels in mouse β-cells (Larsson et al. 1996). Long-chain acyl-CoA is the metabolically active form of FFAs: an important signalling molecule in β-cells (Corkey et al. 2000). Extracellular FFAs enter β-cells and are first acylated by acyl-CoA synthetase to form long-chain acyl-CoA before moving to other pathways. Triacsin C is the inhibitor of acyl-CoA synthetase and inhibits the formation of long-chain acyl-CoA (Omura et al. 1986). It partly inhibited LA-induced activation of KATP channels, suggesting the involvement of LA metabolism in the activation of KATP channels. The slow partial recovery of hyperpolarization after washout of LA also indicates that LA metabolism is involved in the opening of KATP channels.
On the other hand, blockade of LA metabolism only partially inhibited the effects of LA on KATP channels, indicating another signalling pathway is involved in the action of LA on KATP channels. The GPR40 signalling pathway is a newly discovered pathway for FFAs in mediating β-cell function (Briscoe et al. 2003, Itoh et al. 2003). FFAs not only bind to GPR40 as ligands but also cross the β-cells plasma membrane to be metabolized. The metabolic effects of FFAs cannot be fully excluded when FFAs are used to activate GPR40. The discovery of a new molecule, GW9508, sheds light on the research in GPR40. GW9508 is a small-molecule agonist of FFA's membrane receptor GPR40 (Briscoe et al. 2006, Sum et al. 2007). GW9508 induced opening of KATP channels in a manner similar to that of LA under triacsin C treatment. This supports the view that GPR40 activation also takes part in the activation of KATP channels. Moreover, compared with the effects of LA on KATP channels, GW9508-induced opening of KATP channels was recovered fully and quickly, suggesting that its effect is mediated by the membrane receptor. In addition, GH3 cells with KATP channels but without GPR40 expression did not show KATP current change to the action of GW9508. This suggests that the effects of GW9508 on KATP channels are mediated by GPR40.
The involvement of GPR40 in the activation of KATP channels describes a new mechanism for FFAs to regulate KATP channels and GSIS. There are two apparently conflicting hypotheses regarding the regulation of β-cell function by FFAs. First, considerable evidence supports the notion that intracellular metabolism of FFAs is essential to their effects on β-cells (Haber et al. 2006). On the other hand, the role of GPR40 receptor in FFA-induced insulin secretion is reported (Itoh et al. 2003). The results of our experiments demonstrate that both signalling pathways mediate the effects of FFAs on KATP channels. This result may suggest a complimentary action of the two pathways in the functional regulation of β-cells. GPR40 knockout mice do not express dysfunction in GSIS (Steneberg et al. 2005, Latour et al. 2007). However, GPR40-overexpressing mice have impaired GSIS (Steneberg et al. 2005), the mechanism of which was not understood. Our study demonstrates that activation of KATP channels due to overexpression of GPR40 may be responsible for the impaired GSIS in GPR40-overexpressing mice.
We attempted to clarify the molecular mechanism of LA-induced activation of KATP channels. Both activation of GPR40 and FFA metabolites can activate PKC (Poitout 2003) and GPR40 may also activate PKA (Feng et al. 2006). H89 is a cell-permeable and potent inhibitor of PKA with IC50 of 50 nM (Chijiwa et al. 1990). Chelerythrine is a potent and selective PKC inhibitor with IC50 of 0.66 µM (Herbert et al. 1990). By inhibiting these protein kinases by H89 and chelerythrine, we found that neither PKA nor PKC signalling pathways take part in the effects of LA on KATP channels. Further research is required to clarify the molecular mechanisms of intracellular metabolites of FFAs and GR40-mediated activation of KATP channels.
In conclusion, our study demonstrates that both intracellular metabolites and GPR40 membrane receptors take part in LA-induced opening of KATP channels. This describes a new mechanism for FFA-induced impairment of GSIS. The present study provides new data to revaluate the role of GPR40 in pancreatic β-cells.
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Declaration of interest |
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Funding |
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Acknowledgements |
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References |
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Branstrom R, Aspinwall CA, Valimaki S, Ostensson CG, Tibell A, Eckhard M, Brandhorst H, Corkey BE, Berggren PO & Larsson O 2004 Long-chain CoA esters activate human pancreatic β-cell KATP channels: potential role in type 2 diabetes. Diabetologia 47 277–283.[CrossRef][Web of Science][Medline]
Braun JE & Scheller RH 1995 Cysteine string protein, a DnaJ family member, is present on diverse secretory vesicles. Neuropharmacology 34 1361–1369.[CrossRef][Web of Science][Medline]
Briscoe CP, Tadayyon M, Andrews JL, Benson WG, Chambers JK, Eilert MM, Ellis C, Elshourbagy NA, Goetz AS, Minnick DT et al. 2003 The orphan G protein-coupled receptor GPR40 is activated by medium and long chain fatty acids. Journal of Biological Chemistry 278 11303–11311.
Briscoe CP, Peat AJ, McKeown SC, Corbett DF, Goetz AS, Littleton TR, McCoy DC, Kenakin TP, Andrews JL, Ammala C et al. 2006 Pharmacological regulation of insulin secretion in MIN6 cells through the fatty acid receptor GPR40: identification of agonist and antagonist small molecules. British Journal of Pharmacology 148 619–628.[CrossRef][Web of Science][Medline]
Chijiwa T, Mishima A, Hagiwara M, Sano M, Hayashi K, Inoue T, Naito K, Toshioka T & Hidaka H 1990 Inhibition of forskolin-induced neurite outgrowth and protein phosphorylation by a newly synthesized selective inhibitor of cyclic AMP-dependent protein kinase, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), of PC12D pheochromocytoma cells. Journal of Biological Chemistry 265 5267–5272.
Corkey BE, Deeney JT, Yaney GC, Tornheim K & Prentki M 2000 The role of long-chain fatty acyl-CoA esters in β-cell signal transduction. Journal of Nutrition 130 299S–304S.[Web of Science][Medline]
Faergeman NJ & Knudsen J 1997 Role of long-chain fatty acyl-CoA esters in the regulation of metabolism and in cell signalling. Biochemical Journal 323 1–12.[Web of Science][Medline]
Feng DD, Luo Z, Roh SG, Hernandez M, Tawadros N, Keating DJ & Chen C 2006 Reduction in voltage-gated K+ currents in primary cultured rat pancreatic β-cells by linoleic acids. Endocrinology 147 674–682.
Feng DD, Zhao YF, Luo ZQ, Keating DJ & Chen C 2008 Linoleic acid induces Ca2+-induced inactivation of voltage-dependent Ca2+ currents in rat pancreatic β-cells. Journal of Endocrinology 196 377–384.
Fujiwara K, Maekawa F & Yada T 2005 Oleic acid interacts with GPR40 to induce Ca2+ signaling in rat islet β-cells: mediation by PLC and L-type Ca2+ channel and link to insulin release. American Journal of Physiology. Endocrinology and Metabolism 289 E670–E677.
Gopel SO, Kanno T, Barg S, Weng XG, Gromada J & Rorsman P 2000 Regulation of glucagon release in mouse -cells by KATP channels and inactivation of TTX-sensitive Na+ channels. Journal of Physiology 528 509–520.
Gribble FM & Ashcroft FM 2000 Sulfonylurea sensitivity of adenosine triphosphate-sensitive potassium channels from β cells and extrapancreatic tissues. Metabolism 49 3–6.[Web of Science][Medline]
Haber EP, Ximenes HM, Procopio J, Carvalho CR, Curi R & Carpinelli AR 2003 Pleiotropic effects of fatty acids on pancreatic β-cells. Journal of Cellular Physiology 194 1–12.[CrossRef][Web of Science][Medline]
Haber EP, Procopio J, Carvalho CR, Carpinelli AR, Newsholme P & Curi R 2006 New insights into fatty acid modulation of pancreatic β-cell function. International Review of Cytology 248 1–41.[Web of Science][Medline]
Herbert JM, Augereau JM, Gleye J & Maffrand JP 1990 Chelerythrine is a potent and specific inhibitor of protein kinase C. Biochemical and Biophysical Research Communications 172 993–999.[CrossRef][Web of Science][Medline]
Hess DT, Slater TM, Wilson MC & Skene JH 1992 The 25 kDa synaptosomal-associated protein SNAP-25 is the major methionine-rich polypeptide in rapid axonal transport and a major substrate for palmitoylation in adult CNS. Journal of Neuroscience 12 4634–4641.[Abstract]
Itoh Y, Kawamata Y, Harada M, Kobayashi M, Fujii R, Fukusumi S, Ogi K, Hosoya M, Tanaka Y, Uejima H et al. 2003 Free fatty acids regulate insulin secretion from pancreatic β cells through GPR40. Nature 422 173–176.[CrossRef][Web of Science][Medline]
Kahn BB & Flier JS 2000 Obesity and insulin resistance. Journal of Clinical Investigation 106 473–481.[Web of Science][Medline]
Kamp F, Zakim D, Zhang F, Noy N & Hamilton JA 1995 Fatty acid flip-flop in phospholipid bilayers is extremely fast. Biochemistry 34 11928–11937.[CrossRef][Web of Science][Medline]
Larsson O, Deeney JT, Branstrom R, Berggren PO & Corkey BE 1996 Activation of the ATP-sensitive K+ channel by long chain acyl-CoA. A role in modulation of pancreatic β-cell glucose sensitivity. Journal of Biological Chemistry 271 10623–10626.
Latour MG, Alquier T, Oseid E, Tremblay C, Jetton TL, Luo J, Lin DC & Poitout V 2007 GPR40 is necessary but not sufficient for fatty acid stimulation of insulin secretion in vivo. Diabetes 56 1087–1094.
Leung YM, Ahmed I, Sheu L, Tsushima RG, Diamant NE, Hara M & Gaisano HY 2005 Electrophysiological characterization of pancreatic islet cells in the mouse insulin promoter-green fluorescent protein mouse. Endocrinology 146 4766–4775.[CrossRef][Web of Science][Medline]
Manning Fox JE, Nichols CG & Light PE 2004 Activation of adenosine triphosphate-sensitive potassium channels by acyl coenzyme A esters involves multiple phosphatidylinositol 4,5-bisphosphate-interacting residues. Molecular Endocrinology 18 679–686.
Mikhailov MV & Ashcroft SJ 2000 Interactions of the sulfonylurea receptor 1 subunit in the molecular assembly of β-cell K(ATP) channels. Journal of Biological Chemistry 275 3360–3364.
Mikhailov MV, Mikhailova EA & Ashcroft SJ 2000 Investigation of the molecular assembly of β-cell K(ATP) channels. FEBS Letters 482 59–64.[CrossRef][Web of Science][Medline]
Moller DE & Kaufman KD 2005 Metabolic syndrome: a clinical and molecular perspective. Annual Review of Medicine 56 45–62.[CrossRef][Web of Science][Medline]
Omura S, Tomoda H, Xu QM, Takahashi Y & Iwai Y 1986 Triacsins, new inhibitors of acyl-CoA synthetase produced by Streptomyces sp. Journal of Antibiotics 39 1211–1218.[Medline]
Poitout V 2003 The ins and outs of fatty acids on the pancreatic β cell. Trends in Endocrinology and Metabolism 14 201–203.[CrossRef][Web of Science][Medline]
Rorsman P 1997 The pancreatic β-cell as a fuel sensor: an electrophysiologist's viewpoint. Diabetologia 40 487–495.[CrossRef][Web of Science][Medline]
Shapiro H, Shachar S, Sekler I, Hershfinkel M & Walker MD 2005 Role of GPR40 in fatty acid action on the β cell line INS-1E. Biochemical and Biophysical Research Communications 335 97–104.[CrossRef][Web of Science][Medline]
Steneberg P, Rubins N, Bartoov-Shifman R, Walker MD & Edlund H 2005 The FFA receptor GPR40 links hyperinsulinemia, hepatic steatosis, and impaired glucose homeostasis in mouse. Cell Metabolism 1 245–258.[CrossRef][Web of Science][Medline]
Sum CS, Tikhonova IG, Neumann S, Engel S, Raaka BM, Costanzi S & Gershengorn MC 2007 Identification of residues important for agonist recognition and activation in GPR40. Journal of Biological Chemistry 282 29248–29255.
Unger RH 1995 Lipotoxicity in the pathogenesis of obesity-dependent NIDDM. Genetic and clinical implications. Diabetes 44 863–870.[Abstract]
Wyne KL 2003 Free fatty acids and type 2 diabetes mellitus. American Journal of Medicine 115 29S–36S.[CrossRef][Medline]
Yaney GC & Corkey BE 2003 Fatty acid metabolism and insulin secretion in pancreatic β cells. Diabetologia 46 1297–1312.[CrossRef][Web of Science][Medline]
Yang SK, Parkington HC, Blake AD, Keating DJ & Chen C 2005 Somatostatin increases voltage-gated K+ currents in GH3 cells through activation of multiple somatostatin receptors. Endocrinology 146 4975–4984.
Zhao YF, Xu R, Hernandez M, Zhu Y & Chen C 2003 Distinct intracellular Ca2+ response to extracellular adenosine triphosphate in pancreatic β-cells in rats and mice. Endocrine 22 185–192.[CrossRef][Web of Science][Medline]
Zraika S, Dunlop M, Proietto J & Andrikopoulos S 2002 Effects of free fatty acids on insulin secretion in obesity. Obesity Reviews 3 103–112.[CrossRef][Medline]
Received in final form 14 May 2008
Accepted 11 June 2008
Made available online as an Accepted Preprint 11 June 2008
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