title: Acute metabolic amplification of insulin secretion in mouse islets is mediated by mitochondrial export of metabolites, but not by mitochondrial energy generation.
abstract: OBJECTIVE
  The β-cell metabolism of glucose and of some other fuels (e.g. α-ketoisocaproate) generates signals triggering and acutely amplifying insulin secretion. As the pathway coupling metabolism with amplification is largely unknown, we aimed to narrow down the putative amplifying signals.
  
  
  METHODS
  An experimental design was used which previously prevented glucose-induced, but not α-ketoisocaproate-induced insulin secretion. Isolated mouse islets were pretreated for one hour with medium devoid of fuels and containing the sulfonylurea glipizide in high concentration which closed all ATP-sensitive K(+) channels. This concentration was also applied during the subsequent examination of fuel-induced effects. In perifused or incubated islets, insulin secretion and metabolic parameters were measured.
  
  
  RESULTS
  The pretreatment decreased the islet ATP/ADP ratio. Whereas glucose and α-ketoisovalerate were ineffective or weakly effective, respectively, when tested separately, their combination strongly enhanced the insulin secretion. Compared with glucose, the strong amplifier α-ketoisocaproate caused less increase in NAD(P)H-fluorescence and less mitochondrial hyperpolarization. Compared with α-ketoisovalerate, α-ketoisocaproate caused greater increase in NAD(P)H-fluorescence and greater mitochondrial hyperpolarization. Neither α-ketoacid anion enhanced the islet ATP/ADP ratio during onset of the insulin secretion. α-Ketoisocaproate induced a higher pyruvate content than glucose, slowly elevated the citrate content which was not changed by glucose and generated a much higher acetoacetate content than other fuels. α-Ketoisovalerate alone or in combination with glucose did not increase the citrate content.
  
  
  CONCLUSIONS
  In β-cells, mitochondrial energy generation does not mediate acute metabolic amplification, but mitochondrial production of acetyl-CoA and supplemental acetoacetate supplies cytosolic metabolites which induce the generation of specific amplifying signals.
authors.affiliation: Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technical University of Braunschweig, Mendelssohnstrasse 1, D-38106 Braunschweig, Germany. Electronic address: u.panten@tu-bs.de.
authors.forename: Uwe
authors.initials: U
authors.lastname: Panten
authors.forename: Michael
authors.initials: M
authors.lastname: Willenborg
authors.forename: Kirstin
authors.initials: K
authors.lastname: Schumacher
authors.forename: Asmaa
authors.initials: A
authors.lastname: Hamada
authors.forename: Hany
authors.initials: H
authors.lastname: Ghaly
authors.forename: Ingo
authors.initials: I
authors.lastname: Rustenbeck
mesh_terms: D000090:Acetoacetates / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D019343:Citric Acid / Q000378:metabolism; D005260:Female; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D005453:Fluorescence; D005913:Glipizide / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D045782:Hemiterpenes; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism*; D007651:Keto Acids / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D013453:Sulfonylurea Compounds / Q000494:pharmacology
chemical_list: D000090:Acetoacetates; D045782:Hemiterpenes; D007328:Insulin; D007651:Keto Acids; D013453:Sulfonylurea Compounds; D005182:Flavin-Adenine Dinucleotide; D019343:Citric Acid; D009249:NADP; D000244:Adenosine Diphosphate; C001505:alpha-ketoisovalerate; C013082:alpha-ketoisocaproic acid; D019289:Pyruvic Acid; D000255:Adenosine Triphosphate; D005947:Glucose; D005913:Glipizide
keywords: 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid; Acetoacetate; Acetyl-CoA; BCH; Beta-cell; CCCP; FAD fluorescence; Glucose; KC; KIC; KIV; NAD(P)H; PA; PEP; TMRE; carbonyl cyanide m-chlorophenylhydrazone; fluorescence of oxidized flavoproteins; phenylacetate; phosphoenolpyruvate; reduced pyridine nucleotides (NADH+NADPH); tetramethylrhodamine ethyl ester; α-Ketoisocaproate; α-ketocaproate; α-ketoisocaproate; α-ketoisovalerate