Oleic acid interacts with GPR40 to induce Ca2+ signaling in rat islet beta-cells: mediation by PLC and L-type Ca2+ channel and link to insulin release.
It has long been thought that long-chain free fatty acids (FFAs) stimulate insulin secretion via mechanisms involving their metabolism in pancreatic beta-cells. Recently, it was reported that FFAs function as endogenous ligands for GPR40, a G protein-coupled receptor, to amplify glucose-stimulated insulin secretion in an insulinoma cell line and rat islets. However, signal transduction mechanisms for GPR40 in beta-cells are little known. The present study was aimed at elucidating GPR40-linked Ca(2+) signaling mechanisms in rat pancreatic beta-cells. We employed oleic acid (OA), an FFA that has a high affinity for the rat GPR40, and examined its effect on cytosolic Ca(2+) concentration ([Ca(2+)](i)) in single beta-cells by fura 2 fluorescence imaging. OA at 1-10 microM concentration-dependently increased [Ca(2+)](i) in the presence of 5.6, 8.3, and 11.2 mM, but not 2.8 mM, glucose. OA-induced [Ca(2+)](i) increases at 11.2 mM glucose were inhibited in beta-cells transfected with small interfering RNA targeted to rat GPR40 mRNA. OA-induced [Ca(2+)](i) increases were also inhibited by phospholipase C (PLC) inhibitors, U73122 and neomycin, Ca(2+)-free conditions, and an L-type Ca(2+) channel blocker, nitrendipine. Furthermore, OA increased insulin release from isolated islets at 8.3 mM glucose, and it was markedly attenuated by PLC and L-type Ca(2+) channel inhibitors. These results demonstrate that OA interacts with GPR40 to increase [Ca(2+)](i) via PLC- and L-type Ca(2+) channel-mediated pathway in rat islet beta-cells, which may be link to insulin release.
Fujiwara
Ken
K
Dept. of Physiology, Div. of Integrative Physiology, Jichi Medical School, Minamikawachi, Tochigi 329-0498, Japan.
Maekawa
Fumihiko
F
Yada
Toshihiko
T
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D019301:Oleic Acid / Q000008:administration & dosage*; D051381:Rats; D017208:Rats, Wistar; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D010738:Type C Phospholipases / Q000378:metabolism*
D020746:Calcium Channels, L-Type; C473035:G-protein-coupled receptor 40, rat; D007328:Insulin; D043562:Receptors, G-Protein-Coupled; D019301:Oleic Acid; D010738:Type C Phospholipases; D002118:Calcium