Overnight Culture Unmasks Glucose-induced Insulin Secretion in Mouse Islets Lacking ATP-sensitive K+ Channels by Improving the Triggering Ca2+ Signal

• Published in: The Journal of biological chemistry Vol. 282; no. 20; pp. 14768 - 14776
• Main Authors: Szollosi, Andras, Nenquin, Myriam, Henquin, Jean-Claude
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 18-05-2007; American Society for Biochemistry and Molecular Biology
• Subjects: Adenosine Triphosphate - metabolism; Animals; ATP-Binding Cassette Transporters - metabolism; Calcium - metabolism; Calcium Signaling - genetics; Cells, Cultured; Dose-Response Relationship, Drug; Glucose - pharmacology; Insulin - metabolism; Insulin Secretion; Islets of Langerhans - cytology; Islets of Langerhans - metabolism; Mice; Mice, Knockout; Models, Biological; Multidrug Resistance-Associated Proteins - deficiency; Multidrug Resistance-Associated Proteins - metabolism; Potassium Channels - deficiency; Potassium Channels - metabolism; Potassium Channels, Inwardly Rectifying; Receptors, Drug; Sulfonylurea Receptors; Sweetening Agents - pharmacology; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M701382200

A current model ascribes glucose-induced insulin secretion to the interaction of a triggering pathway (KATP channel-dependent Ca2+ influx and rise in cytosolic [Ca2+]c) and an amplifying pathway (KATP channel-independent augmentation of secretion without further increase of [Ca2+]c). However, several studies of sulfonylurea receptor 1 null mice (Sur1KO) failed to measure significant effects of glucose in their islets lacking KATP channels. We addressed this issue that challenges the model. Compared with controls, fresh Sur1KO islets showed slightly elevated basal [Ca2+]c and insulin secretion. In 15 mm glucose, the absolute rate of secretion was ∼3-fold lower in Sur1KO than control islets, with only poor increase above base line. Overnight culture of Sur1KO islets in 10 mm glucose (not in 5 mm) augmented basal insulin secretion and considerably improved the response to 15 mm glucose, which reached higher values than in control islets, in which culture had little impact. Glucose stimulation during KCl depolarization showed that the amplifying pathway is functional in fresh and cultured Sur1KO islets. The differences in insulin secretion between fresh and cultured Sur1KO islets and between Sur1KO and control islets were not attributable to differences in insulin content, glucose oxidation rate, or synchronization of [Ca2+]c oscillations. The unmasking of glucose-induced insulin secretion in β-cells lacking KATP channels is paradoxically due to improvement in the production of a triggering signal (elevated [Ca2+]c). The results show that KATP channels are not the only transducer of glucose effects on [Ca2+]c in β-cells. They explain controversies in the literature and refute arguments raised against the model implicating an amplifying pathway in glucose-induced insulin secretion.