Ca2+, NAD(P)H and membrane potential changes in pancreatic beta-cells by methyl succinate: comparison with glucose.
The present study was undertaken to determine the main metabolic secretory signals generated by the mitochondrial substrate MeS (methyl succinate) compared with glucose in mouse and rat islets and to understand the differences. Glycolysis and mitochondrial metabolism both have key roles in the stimulation of insulin secretion by glucose. Both fuels elicited comparable oscillatory patterns of Ca2+ and changes in plasma and mitochondrial membrane potential in rat islet cells and clonal pancreatic beta-cells (INS-1). Saturation of the Ca2+ signal occurred between 5 and 6 mM MeS, while secretion reached its maximum at 15 mM, suggesting operation of a K(ATP)-channel-independent pathway. Additional responses to MeS and glucose included elevated NAD(P)H autofluorescence in INS-1 cells and islets and increases in assayed NADH and NADPH and the ATP/ADP ratio. Increased NADPH and ATP/ADP ratios occurred more rapidly with MeS, although similar levels were reached after 5 min of exposure to each fuel, whereas NADH increased more with MeS than with glucose. Reversal of MeS-induced cell depolarization by Methylene Blue completely inhibited MeS-stimulated secretion, whereas basal secretion and KCl-induced changes in these parameters were not affected. MeS had no effect on secretion or signals in the mouse islets, in contrast with glucose, possibly due to a lack of malic enzyme. The data are consistent with the common intermediates being pyruvate, cytosolic NADPH or both, and suggest that cytosolic NADPH production could account for the more rapid onset of MeS-induced secretion compared with glucose stimulation.
Heart
Emma
E
Obesity Research Center, Evans Department of Medicine, Boston University School of Medicine, Boston, MA 02118, USA.
Yaney
Gordon C
GC
Corkey
Richard F
RF
Schultz
Vera
V
Luc
Esthere
E
Liu
Lihan
L
Deeney
Jude T
JT
Shirihai
Orian
O
Tornheim
Keith
K
Smith
Peter J S
PJ
Corkey
Barbara E
BE
D000818:Animals; D002118:Calcium / Q000502:physiology*; D018929:Cell Culture Techniques; D005947:Glucose / Q000494:pharmacology*; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008815:Mice, Inbred Strains; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D009249:NADP / Q000031:analogs & derivatives* / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013386:Succinates / Q000494:pharmacology*
D013386:Succinates; D009249:NADP; C024376:NAADP; D005947:Glucose; D002118:Calcium; C041105:monomethyl succinate