Inhibition of mitochondrial Na+-Ca2+ exchanger increases mitochondrial metabolism and potentiates glucose-stimulated insulin secretion in rat pancreatic islets.
The mitochondrial Na(+)-Ca(2+) exchanger (mNCE) mediates efflux of Ca(2+) from mitochondria in exchange for influx of Na(+). We show that inhibition of the mNCE enhances mitochondrial oxidative metabolism and increases glucose-stimulated insulin secretion in rat islets and INS-1 cells. The benzothiazepine CGP37157 inhibited mNCE activity in INS-1 cells (50% inhibition at IC(50) = 1.5 micro mol/l) and increased the glucose-induced rise in mitochondrial Ca(2+) ([Ca(2+)](m)) 2.1 times. Cellular ATP content was increased by 13% in INS-1 cells and by 49% in rat islets by CGP37157 (1 micro mol/l). Krebs cycle flux was also stimulated by CGP37157 when glucose was present. Insulin secretion was increased in a glucose-dependent manner by CGP37157 in both INS-1 cells and islets. In islets, CGP37157 increased insulin secretion dose dependently (half-maximal efficacy at EC(50) = 0.06 micro mol/l) at 8 mmol/l glucose and shifted the glucose dose response curve to the left. In perifused islets, mNCE inhibition had no effect on insulin secretion at 2.8 mmol/l glucose but increased insulin secretion by 46% at 11 mmol/l glucose. The effects of CGP37157 could not be attributed to interactions with the plasma membrane sodium calcium exchanger, L-type calcium channels, ATP-sensitive K(+) channels, or [Ca(2+)](m) uniporter. In hyperglycemic clamp studies of Wistar rats, CGP37157 increased plasma insulin and C-peptide levels only during the hyperglycemic phase of the study. These results illustrate the potential utility of agents that affect mitochondrial metabolism as novel insulin secretagogues.
Lee
Bumsup
B
Division of Metabolic Diseases, MitoKor, San Diego, California 92121, USA.
Miles
Philip D
PD
Vargas
Leonardo
L
Luan
Peng
P
Glasco
Susan
S
Kushnareva
Yulia
Y
Kornbrust
Elisabeth S
ES
Grako
Kathryn A
KA
Wollheim
Claes B
CB
Maechler
Pierre
P
Olefsky
Jerrold M
JM
Anderson
Christen M
CM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000331:Aequorin / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000032:analysis; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D002998:Clonazepam / Q000031:analogs & derivatives* / Q000494:pharmacology; D015870:Gene Expression; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000032:analysis / Q000037:antagonists & inhibitors*; D013841:Thiazepines / Q000494:pharmacology; D014162:Transfection
D007328:Insulin; D017382:Reactive Oxygen Species; D019831:Sodium-Calcium Exchanger; D013841:Thiazepines; D009243:NAD; D000331:Aequorin; D002998:Clonazepam; C079032:CGP 37157; D000255:Adenosine Triphosphate; D005947:Glucose; D002118:Calcium