Regulation of ATP/ADP in Pancreatic Islets

  1. Ian R. Sweet1,
  2. Daniel L. Cook2,
  3. Eric DeJulio1,
  4. Angela R. Wallen1,
  5. Gamal Khalil3,
  6. James Callis3 and
  7. JoAnna Reems4
  1. 1Robert H. Williams Laboratory, Department of Medicine, University of Washington, Seattle, Washington
  2. 2Department of Physiology and Biophysics, University of Washington, Seattle, Washington
  3. 3Department of Chemistry, University of Washington, Seattle, Washington
  4. 4Puget Sound Blood Center, Seattle, Washington
  1. Address correspondence and reprint requests to Ian R. Sweet, HSB K-165, Box 357710, University of Washington, 1959 NE Pacific St., Seattle, WA 98195-7710. E-mail: isweet{at}u.washington.edu

Abstract

ATP and ADP levels are critical regulators of glucose-stimulated insulin secretion. In many aerobic cell types, the phosphorylation potential (ATP/ADP/Pi) 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/Pi was estimated as a function of time. ATP/ADP/Pi 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/Pi. 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.

Footnotes

    • Accepted November 29, 2003.
    • Received July 2, 2003.
| Table of Contents