Galanin inhibits glucagon-like peptide-1 secretion through pertussis toxin-sensitive G protein and ATP-dependent potassium channels in rat ileal L-cells

Abstract

The neuropeptide galanin is widely distributed in the gastrointestinal tract and exerts several inhibitory effects, especially on intestinal motility and on insulin release from pancreatic -cells. The presence of galanin fibres not only in the myenteric and submucosal plexus but also in the mucosa, prompted us to investigate the regulatory role of galanin, and its mechanism of action, on the secretion of the insulinotropic hormone glucagon-like peptide-1 (GLP-1). Rat ileal cells were dispersed through mechanical vibration followed by moderate exposure to hyaluronidase, DNase I and EDTA, and enriched for L-cells by counterflow elutriation. A 6-to 7-fold enrichment in GLP-1 cell content was registered after elutriation, as compared with the crude cell preparation (929 81 vs 138 14 fmol/10 6 cells). L-cells then accounted for 4-5% of the total cell population. Bombesin induced a time-(15-240 min) and dose-(0·1 nM-1 µM) dependent release of GLP-1. Glucose-dependent insulinotropic peptide (GIP, 100 nM), forskolin (10 µM) and the phorbol ester 12-0-tetradecanoylphorbol-13-acetate (TPA, 1 µM) each stimulated GLP-1 secretion over a 1-h incubation period. Galanin (0·01-100 nM) induced a dose-dependent inhibition of bombesin-and of GIP-stimulated GLP-1 release (mean inhibition of 90% with 100 nM galanin). Galanin also dose-dependently inhibited forskolininduced GLP-1 secretion (74% of inhibition with 100 nM galanin), but not TPA-stimulated hormone release. Pretreatment of cells with 200 ng/ml pertussis toxin for 3 h, or incubation with the ATP-sensitive K + channel blocker disopyramide (200 µM), prevented the inhibition by galanin of bombesin-and GIP-stimulated GLP-1 secretion. These studies indicate that intestinal secretion of GLP-1 is negatively controlled by galanin, that acts through receptors coupled to pertussis toxin-sensitive G protein and involves ATP-dependent K + channels.

Gut chemosensing mechanisms

“…These findings are in line with reported effects of galanin in humans, which include a robust inhibition of gastrointestinal motility together with suppression of several gut peptides including PYY and GLP1 but not GIP (135). Galanin is likely to act via a G i -coupled, pertussis-sensitive galanin receptor (134). Interestingly, recent publications reported significantly elevated plasma galanin levels in patients with obesity and diabetes (136,137).…”

“…Galanin is widely expressed in the ENS and, along with somatostatin, is another inhibitor of EEC secretion. In isolated perfused rat ileum, galanin inhibited GIP-stimulated GLP1 release (132); in vitro, galanin inhibited the secretion of several gut hormones including CCK and GLP1 (133,134). These findings are in line with reported effects of galanin in humans, which include a robust inhibition of gastrointestinal motility together with suppression of several gut peptides including PYY and GLP1 but not GIP (135).…”

Signaling Mechanisms Underlying the Release of Glucagon-Like Peptide 1

“…Several model systems have been developed for the study of GLP-1 secretion in vitro, including partially purified canine or rat L-cells prepared by elutriation (19,20), cultured fetal rat intestinal cells (21), and GLP-1-secreting cell lines such as GLUTag (22), STC-1 (23), and NCI-H716 (24). GLUTag cells were derived from a colonic tumor taken from a transgenic mouse expressing SV40 large T antigen under the control of the proglucagon promoter and secrete GLP-1 in response to a range of physiological stimuli (25).…”

Glucose-Sensing in Glucagon-Like Peptide-1-Secreting Cells

“…These preparations have a maximum L-cell content of ϳ30% and have been used to show that GLP-1 secretion is enhanced by activators of PKA and PKC. Such preparations have also been used to demonstrate that GLP-1 secretion is inhibited by the neurotransmitter galanin, acting through a disopyramide-sensitive pathway that might involve K ATP channel opening (27).…”