Inhibition of insulin secretion via distinct signaling pathways in alpha2-adrenoceptor knockout mice

Abstract

Objective: Adrenaline inhibits insulin secretion through activation of a 2 -adrenoceptors (ARs). These receptors are linked to pertussis toxin-sensitive G proteins. Agonist binding leads to inhibition of adenylyl cyclase, inhibition of Ca 2þ channels and activation of K þ channels. Recently, three distinct subtypes of a 2 -AR were described, a 2A -AR, a 2B -AR and a 2C -AR. At present, it is unknown which of these a 2 -AR subtype(s) may regulate insulin secretion. We used mice deficient in a 2 -ARs to analyze the coupling and role of individual a 2 -AR subtypes in insulin-secreting b cells. Methods: The inhibitory effect of adrenaline on insulin secretion was measured in freshly isolated and cultured wild type (wt) and a 2 -AR knockout (KO) mouse islets in order to examine the receptor subtypes which mediate adrenaline-induced inhibition of insulin secretion. Adenylyl cyclase activity was measured in isolated cultured islets. Membrane potential was measured using the amphotericin B permeabilized patch clamp method in isolated and cultured single islet cells. Results: In wt, a 2A -and a 2C -AR KO mouse islets, adrenaline, 1 mmol/l, inhibited secretion by 83, 80 and 100% respectively. In contrast, in a 2A/2C -AR double KO mouse islets, adrenaline had no effect on stimulated secretion indicating that both a 2A -AR and a 2C -AR, but not a 2B -AR, are functionally expressed in mouse islets. Surprisingly, glucose (16.7 mmol/l)-induced secretion in the presence of 1 mmol/l forskolin was greatly impaired in a 2A -AR KO islets. However, when cAMP levels were increased further by the combination of forskolin (5 mmol/l) and 3-isobutyl-1-methylxanthine (100 mmol/l), secretion was stimulated 2.7-fold (8.5-fold in wt islets). Adrenaline lowered the concentration of cAMP in wt and a 2C -AR KO mouse islets by 74%. Adrenaline also hyperpolarized wt and a 2C -AR KO b cells. In contrast, adrenaline did not inhibit adenylyl cyclase in islets of a 2A -AR KO mice, nor did it hyperpolarize a 2A -AR KO b cells. Conclusion: Adrenaline inhibits insulin release through a 2A -and a 2C -ARs via distinct intracellular signaling pathways.

Leucine Stimulates Insulin Secretion via Down-regulation of Surface Expression of Adrenergic α2A Receptor through the mTOR (Mammalian Target of Rapamycin) Pathway

“…expressed in the pancreatic islets, ␣ 2A AR is the major subtype in regulating insulin release (27). Previous studies revealed that activation of ␣ 2A AR by either electric stimulation or norepinephrine inhibits insulin secretion, which is likely through inhibition of cAMP production (33).…”

“…Previous studies revealed that ␣ 2 AR internalization involves clathrin-coated pits (24). We transiently transfected ␣ 2A AR, the major subtype in regulating insulin release (22,27), into HEK293T cells in which its expression is low, along with clathrin-CFP. We monitored ␣ 2 AR internalization using total internal reflection fluorescent microscopy (TIRF).…”

Endurance Training Activates Pancreatic Islets Amp-Activated Kinase-Uncoupling Protein 2 Pathway and Reduces Insulin Secretion

“…adrenaline, noradrenaline) rise. Catecholamines reduce insulin secretion mainly by adrenergic receptors a (2A) and a (2C)-G protein-mediated decreases in cAMP (Peterhoff et al 2003). Thus, it is possible that exercise training could enhance b-cell responsiveness to catecholamines, and consequently reduce GIIS.…”

G-protein-coupled receptors and islet function—Implications for treatment of type 2 diabetes

“…A recent study explored which of those that is of relevance for the inhibition of insulin secretion by using selective knockout mice (Peterhoff et al, 2003). It was found that adrenaline did not inhibit insulin secretion in mice with a double knockout of α 2A -and α 2C -adrenoceptors, and that the inhibition of insulin secretion by adrenaline was partially reduced in mice with single knockout of these receptors.…”