Triggering and amplification of insulin secretion by dimethyl alpha-ketoglutarate, a membrane permeable alpha-ketoglutarate analogue.
Cytosolic alpha-ketoglutarate is a potential signalling compound at late steps of stimulus-secretion-coupling in the course of insulin secretion induced by glucose and other fuels. This hypothesis is mainly based on the insulin-releasing effect of the membrane permeable ester dimethyl alpha-ketoglutarate which enters the beta-cell and is cleaved to produce cytosolic monomethyl alpha-ketoglutarate and eventually alpha-ketoglutarate. The present study tested this hypothesis. Insulin release, K(ATP) channel currents, membrane potential, ATP/ADP ratio and fluorescence of NAD(P)H (reduced pyridine nucleotides) were measured in mouse pancreatic islets and beta-cells. At a substimulatory glucose concentration (5 mM), dimethyl alpha-ketoglutarate (15 mM) produced a sustained insulin release, but no change of the islet ATP/ADP ratio and NAD(P)H fluorescence. In the absence of glucose, however, dimethyl alpha-ketoglutarate (15 mM) did not stimulate insulin release although it increased the ATP/ADP ratio and NAD(P)H fluorescence. Insulin secretion induced by a maximally effective concentration of the K(ATP) channel-blocking sulfonylurea glipizide was strongly amplified by dimethyl alpha-ketoglutarate in the presence of 5 mM glucose, but only moderately in the absence of glucose. Dimethyl alpha-ketoglutarate directly inhibited K(ATP) channels in inside-out membrane patches, depolarized the plasma membrane of intact beta-cells and generated action potentials. In conclusion, the stimulation of insulin secretion by extracellularly applied dimethyl alpha-ketoglutarate depends on inhibition of beta-cell K(ATP) channels by direct action of dimethyl alpha-ketoglutarate. The metabolism of alpha-ketoglutarate generated intracellularly by ester cleavage contributes to stimulation of insulin secretion both by indirect K(ATP) channel inhibition (via activation of ATP production) and by an amplifying effect.
Willenborg
Michael
M
Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technical University of Braunschweig, Mendelssohnstrasse 1, D-38106 Braunschweig, Germany.
Panten
Uwe
U
Rustenbeck
Ingo
I
D000200:Action Potentials / Q000187:drug effects; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004594:Electrophysiology; D005260:Female; D005453:Fluorescence; D005947:Glucose / Q000008:administration & dosage; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D054086:KATP Channels / Q000037:antagonists & inhibitors*; D007656:Ketoglutaric Acids / Q000493:pharmacokinetics / Q000494:pharmacology*; D051379:Mice; D009249:NADP / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000493:pharmacokinetics / Q000494:pharmacology*
D007328:Insulin; D054086:KATP Channels; D007656:Ketoglutaric Acids; D026902:Potassium Channel Blockers; C541783:dimethyl alpha-ketoglutarate; D009249:NADP; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D005947:Glucose