Oscillations in cytosolic free Ca2+, oxygen consumption, and insulin secretion in glucose-stimulated rat pancreatic islets.
Insulin secretion in the intact organism, and by the perfused pancreas and groups of isolated perifused islets, is pulsatile. We have proposed a metabolic model of glucose-induced insulin secretion in which oscillations in the ATP/ADP ratio drive alterations in metabolic and electrical events that lead to insulin release. A key prediction of our model is that metabolically driven Ca2+ oscillations will also occur. Using the fluorescent Ca2+ probe, fura 2, digital image analysis, and sensitive O2 electrodes, we investigated cytosolic free Ca2+ responses and O2 consumption in perifused rat islets that had been maintained in culture for 1-4 days. We found that elevated ambient glucose increased the average cytosolic free Ca2+ level, the ATP/ADP ratio, and oxygen consumption, as previously found in freshly isolated islets. Oscillatory patterns were obtained for Ca2+, O2 consumption, and insulin secretion in the presence of 10 and 20 mM glucose. Very low amplitude oscillations in cytosolic free Ca2+ were observed at 3 mM nonstimulatory glucose levels. Evaluation of the Ca2+ responses of a large series of individual islets, monitored by digital image analysis and perifused at both 3 and 10 mM glucose, indicated that the rise in glucose concentration caused more than a doubling of the average cytosolic free Ca2+ value and a 4-fold increase in the amplitude of the oscillations with little change in period. The pattern of Ca2+ change within the islets was consistent with recruitment of responding cells. The coexistence of oscillations with similar periods in insulin secretion, oxygen consumption, and cytosolic free Ca2+ is consistent with the model of metabolically driven pulsatile insulin secretion.
Longo
E A
EA
Evans Department of Medicine, Boston University School of Medicine, Massachusetts 02118.
Tornheim
K
K
Deeney
J T
JT
Varnum
B A
BA
Tillotson
D
D
Prentki
M
M
Corkey
B E
BE
D000227:Adenine Nucleotides / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000494:pharmacology*; D005905:Glyburide / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D008297:Male; D010101:Oxygen Consumption; D010507:Periodicity; D051381:Rats; D011919:Rats, Inbred Strains; D012636:Secretory Rate
D000227:Adenine Nucleotides; D007328:Insulin; D005947:Glucose; D005905:Glyburide; D002118:Calcium