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RESEARCH COMMUNICATION |
a Department of Science and Technology and Institute of Bioengineering, Campus de San Juan, Miguel Hernandez University, Alicante, Spain
b Department of Biochemistry, Veterinary Faculty, Complutense University, Madrid, Spain
c Department of Physiology and Institute of Bioengineering, Campus de San Juan, Miguel Hernandez University, Alicante, Spain
In pancreatic ß-cells, stimulatory glucose concentrations increase cytosolic diadenosine polyphosphates ([ApnA]i) to concentrations sufficient to block ATP-sensitive K+ (KATP) channels. High-performance liquid chromatography and patch clamp techniques were used to study the metabolic pathways by which pancreatic ß-cells synthesize ApnA and the mechanism through which ApnA inhibit KATP channels. ApnA show a glucose- and time-dependent cytosolic concentration increase parallel, though 30- to 50-fold higher, to changes observed in adenine nucleotides. Other fuel secretagogues, leucine and 2-ketoisocaproate, raise [ApnA]i as efficiently as 22 mM glucose. Blockade of glycolysis or Krebs cycle decreases glucose-induced [ApnA]i. No significant increase in cytosolic ApnA concentrations is induced by nonnutrient secretagogues or nonmetabolizable nutrient secretagogues. Inorganic pyrophosphatase inhibition with sodium fluoride blocks 22 mM glucose-induced [ApnA]i increase. ApnA inhibition of KATP channel resembles that of ATP in efficacy, but shows clear functional differences. Unlike ATP, Ap4A does not restore channel activity after rundown. Furthermore, these compounds do not compete with each other for the same site. These features suggest a prominent role for Ap4A in ß-cell function, comparable to ATP. We conclude that nutrient metabolism through pyrophosphatase activation is necessary to induce ApnA synthesis, which in turn constitutes a new, ATP-independent, metabolic regulator of KATP channel activity.—Martín, F., Pintor, J., Rovira, J. M., Ripoll, C., Miras-Portugal, M. T., Soria, B. Intracellular diadenosine polyphosphates: a novel second messenger in stimulus-secretion coupling. FASEB J. 12, 1499–1506 (1998)
Key Words: KATP channel • pancreatic ß-cell • stimulus-secretion coupling • diabetes
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