β-Cell Secretory Products Activate α-Cell ATP-Dependent Potassium Channels to Inhibit Glucagon Release
Article Figures & Tables
Figures
- FIG. 1.
Quantitative comparison of zinc (A) and insulin (B) secretion from batch-incubated islets in response to 2.5 or 16 mmol/l glucose. Data are means ± SE, n ≥ 3, *P < 0.005. Dose response of glucagon (C) or insulin (D) secretion from static-incubated islets to zinc in the presence of 0 (C) or 10 (D) mmol/l glucose. E and F: Membrane potential recordings from isolated α-cells using the perforated-patch whole-cell configuration. Response of electrical activity to zinc (0.3–30 μmol/l, E) and zinc (30 μmol/l) with Ca2+EDTA (2.5 mmol/l, F). G: Dose response of spike frequency to zinc. Data are means ± SE, n = 6, *P < 0.05, **P < 0.001.
- FIG. 2.
A and B: Glucagon secretion from FACS-isolated adherent α-cells incubated for 30 min in the presence of basal (2.5 mmol/l) glucose. Where indicated, incubation medium included tolbutamide (100 μmol/l), monomethylsuccinate (10 mmol/l), pyruvate (5 mmol/l), GLP-1 (10 nmol/l), isobutylmethylxanthine (IBMX) (100 μmol/l), and forskolin (1 μmol/l). EGTA (10 mmol/l) or glucose was increased to 16 mmol/l. Secreted glucagon was calculated as percent of content and is expressed here relative to basal (100%). A: Inset: Glucagon secretion from dispersed islets, incubated for 60 min in 2.5 or 16 mmol/l glucose (n = 3). Data are means ± SE, n ≥ 3, *P < 0.01, **P < 0.005. C and D: Membrane potential recordings from isolated α-cells using the perforated-patch whole-cell configuration in glucose-free basal conditions. Where indicated (bar), superfusate included glucose (15 mmol/l), pyruvate (2 mmol/l), or tolbutamide (0.1 mmol/l). Recordings are typical of seven cells.
- FIG. 3.
A: Glucagon secretion from isolated α-cells incubated for 30 min in basal (0 mmol/l) glucose conditions. Where indicated, incubation medium included glucose (16 mmol/l) or pyruvate (5 mmol/l) or arginine (10 mmol/l) ± zinc (30 μmol/l). Secreted glucagon was calculated as percent of content and is expressed relative to basal (100%). Data are means ± SE, n = 3, *P < 0.05. Whole-cell patch-clamp recordings of KATP channel current activity in isolated α-cells, exposed to zinc (30 μmol/l) (B) or zinc and Ca2+ EDTA (2.5 mmol/l) and subsequently diazoxide (0.1 mmol/l) (C). Traces are representative of seven or more experiments. D: Relative increases in K+ current amplitude in response to zinc, where I = current in presence of zinc and Io = current under control conditions. EC50 = 2.2 μmol/l with cooperativty factor of 1.1. Data are means ± SE, n = 7 for each point. Diazoxide (100 μmol/l) increased relative current amplitude (I/Io) to 3.2 ± 0.3, n = 6. E: Relative transcript abundance of KATP channel subunits Kir6.2 and SUR1 in FACS-isolated α- and β-cells, quantified by real-time RT-PCR. Data are presented relative to β-cells (1), n = 3, *P < 0.05.
- FIG. 4.
A: Relative abundance of insulin receptor and GLP-1 receptor transcripts in FACS-isolated α- and β-cells quantified by real-time RT-PCR and compared with liver. Transcript for GLP-1 receptor was not detected (nd) in α-cell or liver cDNA. Data are presented relative to β-cells (1), n ≥ 3, *P < 0.05, **P < 0.01. B–D: Analysis of islet hormone secretion after 1-h static incubations. Glucagon secretion was compared in 2.5 vs. 16 mmol/l glucose in the absence (□) or presence ([cjs2112]) of insulin antiserum (B) or “zinc-free” exogenous insulin (100 ng/ml) (C). Endogenous insulin secretion was investigated by measuring cosecreted C-peptide (D) in 2.5 mmol/l glucose in the presence or absence of monomethylsuccinate (10 mmol/l) and exogenous insulin (100 ng/ml, [cjs2112]). Similar results were obtained with high glucose (not shown). Secreted hormone data are expressed as percent of content and are means ± SE of four (B and C) or three (E) independent experiments. **P < 0.01.
- FIG. 5.
A: Glucagon secretion from in situ–perfused rat pancreata measured in basal (2.8 mmol/l) glucose conditions and upon stimulation with pyruvate at 15 min (10 mmol/l, 30-min duration). Exogenous “zinc-free” insulin was included for the indicated time period (bar). C-peptide secretion, analyzed in the same experiments, confirmed that endogenous insulin secretion was unaltered on exposure to pyruvate or exogenous insulin (not shown). Data are means ± SE of six independent perfusions. B: Membrane potential recording from an isolated α-cell using the perforated-patch whole-cell configuration. Electrical activity response to “zinc-free” insulin (100 ng/ml) was analyzed and the effect on spike frequency calculated (C). The recording is typical of six cells and data are means ± SE of six experiments. D: Glucagon secretion from isolated α-cells measured after a 15-min static incubation in basal (2.5 mmol/l) glucose conditions in the presence or absence of pyruvate (5 mmol/l), insulin (100 ng/ml), or wortmanin (100 nmol/l), as indicated. Secreted glucagon was calculated as percent of content and shown here relative to basal (100%). Data are means ± SE of more than or equal to four experiments. *P < 0.05, **P < 0.005. E: KATP channel current activity measured in isolated α-cells by whole-cell patch clamp. Relative changes in K+ current amplitude are shown, where I = current in the presence of insulin (100 ng/ml) and/or wortmannin (100 nmol/l) and Io = current under control conditions. Insulin-induced changes in K+ current were transient. Data were collected 6 min after hormone addition when the effect was maximal. Data are means ± SE, n ≥ 5, *P < 0.05.
In this Issue
