Distinguishing features of leucine and alpha-ketoisocaproate sensing in pancreatic beta-cells.
Culturing rat islets in high glucose (HG) increased 1-(14)C-alpha-ketoisocaproate (KIC) oxidation compared with culturing them in low glucose. Leucine caused insulin secretion (IS) in low glucose but not in HG rat islets, whereas KIC did so in both. Pretreatment with HG for 40 min abolished leucine stimulation of IS by mouse islets and prevented the cytosolic Ca(2+) rise without inhibiting IS and Ca(2+) increments caused by KIC. When islets were pretreated without glucose and glutamine, aminooxyacetic acid (AOA) markedly decreased KIC effects. When islets were pretreated without glucose and with glutamine, AOA potentiated leucine effects but attenuated KIC effects. AOA stimulated glutamine oxidation in the presence but not the absence of +/-2-amino-2-norbornane-carboxylic acid, a nonmetabolized leucine analog. Pretreatment with HG and glutamine partially reversed AOA inhibition of KIC effects. Glucose increased intracellular ATP and GTP, whereas it decreased ADP and GDP in beta HC9 cells. Glutamate dehydrogenase activity of beta HC9 cell extracts was increased by leucine and attenuated by GTP, but it was potentiated by ADP. In conclusion, leucine and KIC stimulated beta-cells via distinct mechanisms. Glutamate dehydrogenase is the sensor of leucine, whereas transamination plays an important role in KIC stimulation of pancreatic beta-cells.
Gao
Zhiyong
Z
Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine and The Children's Hospital, Philadelphia, Pennsylvania 19104, USA.
Young
Robert A
RA
Li
Guizhu
G
Najafi
Habiba
H
Buettger
Carol
C
Sukumvanich
Siam S
SS
Wong
Ryan K
RK
Wolf
Bryan A
BA
Matschinsky
Franz M
FM
D000625:Aminooxyacetic Acid / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002457:Cell Extracts / Q000737:chemistry; D002460:Cell Line; D002628:Chemoreceptor Cells / Q000502:physiology*; D046508:Culture Techniques; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000008:administration & dosage; D005969:Glutamate Dehydrogenase / Q000032:analysis; D005973:Glutamine / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007425:Intracellular Membranes / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000294:innervation* / Q000378:metabolism; D007651:Keto Acids / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism*; D051379:Mice; D008815:Mice, Inbred Strains; D009711:Nucleotides / Q000494:pharmacology / Q000502:physiology; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar
D002457:Cell Extracts; D007328:Insulin; D007651:Keto Acids; D009711:Nucleotides; D005973:Glutamine; D000625:Aminooxyacetic Acid; C013082:alpha-ketoisocaproic acid; D005969:Glutamate Dehydrogenase; D007930:Leucine; D005947:Glucose; D002118:Calcium