Regulation of ATP/ADP in pancreatic islets.
ATP and ADP levels are critical regulators of glucose-stimulated insulin secretion. In many aerobic cell types, the phosphorylation potential (ATP/ADP/P(i)) is controlled by sensing mechanisms inherent in mitochondrial metabolism that feed back and induce compensatory changes in electron transport. To determine whether such regulation may contribute to stimulus-secretion coupling in islet cells, we used a recently developed flow culture system to continuously and noninvasively measure cytochrome c redox state and oxygen consumption as indexes of electron transport in perifused isolated rat islets. Increasing substrate availability by increasing glucose increased cytochrome c reduction and oxygen consumption, whereas increasing metabolic demand with glibenclamide increased oxygen consumption but not cytochrome c reduction. The data were analyzed using a kinetic model of the dual control of electron transport and oxygen consumption by substrate availability and energy demand, and ATP/ADP/P(i) was estimated as a function of time. ATP/ADP/P(i) increased in response to glucose and decreased in response to glibenclamide, consistent with what is known about the effects of these agents on energy state. Therefore, a simple model representing the hypothesized role of mitochondrial coupling in governing phosphorylation potential correctly predicted the directional changes in ATP/ADP/P(i). Thus, the data support the notion that mitochondrial-coupling mechanisms, by virtue of their role in establishing ATP and ADP levels, may play a role in mediating nutrient-stimulated insulin secretion. Our results also offer a new method for continuous noninvasive measures of islet cell phosphorylation potential, a critical metabolic variable that controls insulin secretion by ATP-sensitive K(+)-dependent and -independent mechanisms.
Sweet
Ian R
IR
Robert H. Williams Laboratory, Department of Medicine, University of Washington, Seattle, Washington, USA. isweet@u.washington.edu
Cook
Daniel L
DL
DeJulio
Eric
E
Wallen
Angela R
AR
Khalil
Gamal
G
Callis
James
J
Reems
JoAnna
J
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D045304:Cytochromes c / Q000187:drug effects / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D006706:Homeostasis; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects; D011190:Potassium Cyanide / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344
D007004:Hypoglycemic Agents; D000244:Adenosine Diphosphate; D000968:Antimycin A; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D005947:Glucose; D011190:Potassium Cyanide; D005905:Glyburide