Glucose-stimulated insulin secretion correlates with changes in mitochondrial and cytosolic Ca2+ in aequorin-expressing INS-1 cells.
Nutrient-stimulated insulin secretion is dependent upon the generation of metabolic coupling factors in the mitochondria of the pancreatic B cell. To investigate the role of Ca2+ in mitochondrial function, insulin secretion from INS-1 cells stably expressing the Ca2+-sensitive photoprotein aequorin in the appropriate compartments was correlated with changes in cytosolic calcium ([Ca2+]c) and mitochondrial calcium ([Ca2+]m). Glucose and KCl, which depolarize the cell membrane, as well as the Ca2+-mobilizing agonist, carbachol (CCh), cause substantial increases in [Ca2+]m which are associated with smaller rises in [Ca2+]c. The L-type Ca2+-channel blocker, SR7037, abolished the effects of glucose and KCl while attenuating the CCh response. Glucose-induced increases in [Ca2+]m, [Ca2+]c, and insulin secretion all demonstrate a pronounced initial peak followed by a sustained plateau. All three parameters are increased synergistically when glucose and CCh are combined. Finally, [Ca2+]m, [Ca2+]c, and insulin secretion also display desensitization phenomena following repeated additions of the three stimuli. The high sensitivity of [Ca2+]m to Ca2+ influx and the desensitization-resensitization effects can be explained by a model in which the mitochondria of INS-1 cells are strategically located to sense Ca2+ influx through plasma membrane Ca2+ channels. In conclusion, the correlation of [Ca2+]m and [Ca2+]c with insulin secretion may indicate a fundamental role for Ca2+ in the adaptation of oxidative metabolism to the generation of metabolic coupling factors and the energy requirements of exocytosis.
Kennedy
E D
ED
Department of Medicine, University of Geneva, Switzerland.
Rizzuto
R
R
Theler
J M
JM
Pralong
W F
WF
Bastianutto
C
C
Pozzan
T
T
Wollheim
C B
CB
D000331:Aequorin / Q000096:biosynthesis*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D004164:Diphosphonates / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008163:Luminescent Measurements; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011994:Recombinant Proteins / Q000096:biosynthesis; D014162:Transfection
D002121:Calcium Channel Blockers; D004164:Diphosphonates; D007328:Insulin; D011994:Recombinant Proteins; C061154:belfosdil; D000331:Aequorin; D011189:Potassium Chloride; D002217:Carbachol; D005947:Glucose; D002118:Calcium