101-OR: Revelations in Regulation—Sodium/Potassium ATPase Subunit Control of Beta-Cell Cation Handling and Insulin Secretion

Background and Aims: Na⁺/K⁺ ATPases (NKAs) control ß-cell Ca²⁺ influx and insulin secretion by integrating the signal strength of stimulatory (G_s) and inhibitory (G_i) G protein-coupled receptors (GPCRs). However, there is a significant gap in our understanding of how specific NKA subunits contribute to ß-cell function. Therefore, due to the importance of NKA-mediated cation handling to islet function, we set out to provide a clear understanding of the roles of NKA subunits in tuning β-cell Ca²⁺ handling and hormone secretion.

Materials and Methods: Electrophysiology, fluorescence imaging, and hormone secretion assays were employed to study NKA subunit regulation of ß-cell function. A transgenic mouse model with ß-cell knockout of NKAß1 (ßNKAß1KO) was used to determine the importance of this subunit. Human pseudoislets were generated with ß-cell-restricted NKAß1 knockdown (ßNKAß1KD) to investigate the function of this subunit in human islets.

Results: NKAß1 KO increased ß-celI Na⁺ by 45±1% (P<0.001) and diminished SST-induced NKA currents by 37±6% (P<0.05). Glucose-stimulated Ca²⁺ influx into ßNKAß1KO islets was delayed by 143±28 seconds (P<0.01) and Ca²⁺ plateau fraction reduced by 30±3% (P<0.01). ßNKAß1KO mice displayed glucose intolerance (36±17% AUC increase; P<0.5). Glucose-stimulated insulin secretion (GSIS; 9 mM glucose (G)) was decreased by 19±2% from ßNKAß1KO mouse islets (P<0.05) and by 36±11% from human ßNKAß1KD islets (11G; P<0.05). G_i signaling-mediated ßNKAß1KO islet Ca²⁺ decreases were amplified by 30±7% (P<0.01) and 46±9% (P<0.01) for SSTRs and αADRs respectively. Islet Ca²⁺ increases due to activation of G_s-coupled GLP1Rs were decreased by 23±6% (P<0.05).

Conclusion: NKAß1 serves a critical role in maintaining the driving force for Na⁺ entry into ß-cells as well as by shaping the capacity of G_i- and G_s-GPCRs to tune NKA function. Together these findings establish NKAß1 as a key regulator of mouse and human ß-cell function.