1100-OR: The Sodium/Potassium ATPase Complex: A Central Regulator of Sodium-Dependent Alpha-Cell Calcium Handling and Glucagon Secretion

Introduction and Objective: Precise control of α-cell glucagon secretion is essential for glucose homeostasis, yet the mechanisms coupling α-cell nutrient sensing and hormone secretion remain incomplete. As a primary consumer of ATP, Na+/K+ ATPases (NKAs) are positioned to translate changes in nutrient availability into ionic regulation of α-cell glucagon secretion. Therefore, our objective was to determine the physiological role of NKA complexes in governing glucose-dependent control of Na+ and Ca2+ fluxes required for glucagon secretion. Methods: Electrophysiology, fluorescence imaging, and hormone secretion assays were used to study how NKA regulates α-cell function. To reduce plasma membrane NKA, we targeted the NKAβ1 trafficking subunit using α-cell-specific knockout mice (NKAβ1Δα) and human pseudoislets with α-cell-specific NKAβ1 knockdown (NKAβ1αKD). Results: NKAβ1Δα mice were glucose intolerant (37±14% AUC increase; P<0.05). Under hyperglycemic conditions (11 mM glucose) α-cell Ca2+ was elevated 110±31% in NKAβ1Δα islets compared to controls (P<0.05). Although glucagon secretion from NKAβ1Δα islets was suppressed by 11 mM glucose, following a switch to hypoglycemia (1 mM glucose), Ca2+ in control α-cells rose by 174±30% (P<0.01) whereas NKAβ1Δα α-cell Ca2+ remained elevated. Interestingly, glucose-mediated inhibition of Ca2+ influx was delayed and Na+ levels were elevated for NKAβ1Δα α-cells at low glucose compared to controls. Moreover, hypoglycemia-induced glucagon secretion increased by 357±25% (P<0.01) in NKAβ1Δα mouse islets and 158±22% (P<0.01) in NKAβ1αKD human pseudoislets compared to controls. Electrophysiological recordings revealed that the defect in Ca2+ handling is due in part to greater depolarization of NKAβ1Δα α-cells. Conclusion: These results establish NKAβ1 as a critical metabolic transducer in α-cells, where it maintains the ionic and electrical gradients necessary to couple glucose sensing with glucagon secretion. Disclosure M. Dickerson: None. P. Dadi: None. J.R. Dobson: None. S. Behera: None. D. Jacobson: None. Funding Vanderbilt Integrated Training in Engineering and Diabetes grant (T32DK101003), an Initiative for Maximizing Student Development at Vanderbilt grant (T32GM139800), a Multidisciplinary Training in Molecular Endocrinology grant (T32DK007563), National Institutes of Health grants (DK-097392, DK-115620, DK-129340, and DK-136768), an American Diabetes Association Grant (1-17-IBS-024), a Juvenile Diabetes Research Foundation grant (2-SRA-2019-701-S-B), a grant from The Leona M & Harry B. Helmsley Charitable Trust (2306-06066), and a Pilot and Feasibility grant through the Vanderbilt Diabetes Research and Training Center grant (P60-DK-20593).