1658-P: Hyperpolarization as a Driver of Alpha-Cell Function—The Role of Sodium/Potassium ATPases in Glucose-Regulated Glucagon Secretion

Introduction and Objective: The catalytic (NKAα1) and auxiliary (NKAβ1) subunits of the NKA protein complex are highly expressed in α-cells, yet their influence is poorly understood. Given the importance of NKA to cation handling and membrane potential regulation, we aimed to define the role of NKA in tuning α-cell Ca²⁺-handling and glucagon secretion.Methods: Electrophysiology, fluorescence imaging, and hormone secretion assays were employed to study NKA subunit-specific regulation of α-cell function. Transgenic mice with α-cell-specific NKAβ1 (αNKAβ1KO) or NKAα1 (αNKAα1KO) knockout and a ratiometric Ca²⁺ indicator (Salsa6f) were utilized to examine the function of α-cell NKA. These mouse lines utilized two α-cell-specific Cre lines, a constitutive Gcg^iCre and a conditional Gcg-creERT2. Furthermore, human pseudoislets with α-cell-specific NKAβ1 knockdown (αNKAβ1KD) were generated to investigate the role of this subunit in human α-cells.Results: α-cell Ca²⁺ was elevated 210±31% in αNKAβ1KO islets compared to controls at 11 mM glucose (11G; P<0.05); NKAβ1KO α-celI Ca²⁺ was unchanged at low glucose (1G), while control α-celI Ca²⁺ increased 274±30% (P<0.01). Glucagon secretion at 1G decreased 40±15% (P<0.01) from αNKAβ1KO islets and 23±11% (P<0.05) from αNKAβ1KD human pseudoislets. αNKAβ1KO mice were glucose intolerant (37±14% increase in AUC; P<0.05), and plasma glucagon decreased 71±12% in αNKAβ1KO mice compared to controls after an insulin tolerance test (ITT; P<0.001). Salsa6f-positive α-cells were present 7 days post-tamoxifen in αNKAα1KO islets, indicating NKAα1 loss does not cause rapid cell death. Seven days post-tamoxifen, glucagon secretion at 1G from αNKAα1KO islets decreased 70±12% (P<0.01) and plasma glucagon decreased 62±13% (P<0.01) in response to an ITT.Conclusion: These findings establish NKAα1 and β1 as key regulators of mouse and human α-cell function. This also suggests that glucose control of NKA activity likely promotes glucose inhibition of glucagon secretion.

M. Dickerson: None. P. Dadi: None. J. Dobson: None. S. Behera: None. S. Peachee: None. S. Gibson: None. D. Jacobson: None.

Vanderbilt ITED (T32DK101003); NIH (R01 DK136768, R01 DK09739, and R01 DK115620)



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