title: Anaplerosis via pyruvate carboxylase is required for the fuel-induced rise in the ATP:ADP ratio in rat pancreatic islets.
abstract: OBJECTIVE
  The molecular mechanisms of insulin release are only partially known. Among putative factors for coupling glucose metabolism to insulin secretion, anaplerosis has lately received strong support. The anaplerotic enzyme pyruvate carboxylase is highly expressed in beta cells, and anaplerosis influences insulin secretion in beta cells. By inhibiting pyruvate carboxylase in rat islets, we aimed to clarify the hitherto unknown metabolic events underlying anaplerotic regulation of insulin secretion.
  
  
  METHODS
  Phenylacetic acid (5 mmol/l) was used to inhibit pyruvate carboxylase in isolated rat islets, which were then assessed for insulin secretion, fuel oxidation, ATP:ADP ratio, respiration, mitochondrial membrane potential, exocytosis and ATP-sensitive K(+) channel (K(ATP)-channel) conductance.
  
  
  RESULTS
  We found that the glucose-provoked rise in ATP:ADP ratio was suppressed by inhibition of pyruvate carboxylase. In contrast, fuel oxidation, respiration and mitochondrial membrane potential, as well as Ca(2+)-induced exocytosis and K(ATP)-channel conductance in single cells, were unaffected. Insulin secretion induced by alpha-ketoisocaproic acid was suppressed, whereas methyl-succinate-stimulated secretion remained unchanged. Perifusion of rat islets revealed that inhibition of anaplerosis decreased both the second phase of insulin secretion, during which K(ATP)-independent actions of fuel secretagogues are operational, as well as the first and K(ATP)-dependent phase.
  
  
  CONCLUSIONS
  Our results are consistent with the concept that anaplerosis via pyruvate carboxylase determines pyruvate cycling, which has previously been shown to correlate with glucose responsiveness in clonal beta cells. These processes, controlled by pyruvate carboxylase, seem crucial for generation of an appropriate ATP:ADP ratio, which may regulate both phases of fuel-induced insulin secretion.
authors.affiliation: Department of Experimental Medical Science,Division of Diabetes, Metabolism, and Endocrinology, Lund University, Lund, Sweden. ulrika.fransson@med.lu.se
authors.forename: U
authors.initials: U
authors.lastname: Fransson
authors.forename: A H
authors.initials: AH
authors.lastname: Rosengren
authors.forename: F C
authors.initials: FC
authors.lastname: Schuit
authors.forename: E
authors.initials: E
authors.lastname: Renström
authors.forename: H
authors.initials: H
authors.lastname: Mulder
mesh_terms: D000244:Adenosine Diphosphate / Q000032:analysis*; D000255:Adenosine Triphosphate / Q000032:analysis*; D000818:Animals; D002478:Cells, Cultured; D005260:Female; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D005973:Glutamine / Q000378:metabolism / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000737:chemistry* / Q000187:drug effects* / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D010084:Oxidation-Reduction; D019308:Palmitic Acid / Q000378:metabolism / Q000494:pharmacology; D011766:Pyruvate Carboxylase / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D007328:Insulin; D005973:Glutamine; D019308:Palmitic Acid; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D011766:Pyruvate Carboxylase; D005947:Glucose