SAT061 Deficiency Of ENaC Excites Pancreatic β Cells To Promote Insulin Secretion

Abstract

Abstract Disclosure: Y. Que: None. X. Ma: None. Y. Wu: None. J. Chen: None. J. Guo: None. Y. Ruan: None. In response to glucose elevation or other physiological stimuli, pancreatic islet β cells are excited to mobilize intracellular Ca2+ leading to insulin secretion, which is a complex cellular event with underlying mechanisms not fully elucidated. The present study explored possible involvement of the epithelial Na+ channel (ENaC) in β cell excitability and insulin secretion. Analyzing human databases, primary rat/mouse pancreatic tissues as well as RINm5F, a rat β-cell line, we confirmed the expression of Scnn1a, Scnn1b and Scnn1g genes (encoding ENaC subunits, α, β and γ, respectively) in human and rodent β cells. To our surprise, inhibiting this Na+ channel by selective blockers, amiloride (1-10 µM) or benzamil (1 µM), did not retard insulin secretion, but instead triggered a slow membrane depolarization with electrical bursts (41.5 ± 5.9 mV, measured by patch-clamp, n = 5-6), elicited substantial Ca2+ oscillations (135.2 ± 2.5% of baseline, by Fura-2 imaging, n = 256-380) and promoted insulin secretion (158.2 ± 25.6% of control, by ELISA, t-test, p < 0.05, n = 6) in RINm5F or isolated mouse β cells. siRNA-based knockdown of ENaCα, the rate-limiting subunit of ENaC, in RINm5F cells confirmed that deficiency of ENaC induced a significant increase in insulin secretion (230.2 ± 20.2% of control, t-test, p < 0.001, n = 6). Proteomic analysis of RINm5F cells (n = 5) through mass spectrometry showed that signaling pathways key to glucose metabolism and insulin secretion were significantly activated in RINm5F cells with ENaC knockdown in comparison with control cells, consistently suggesting a role of ENaC deficiency in exciting β cells to release insulin. We next built a mouse model with β cell-specific knockout of ENaCα (Scnn1afl/fl, Ins1-Cre+), which exhibited disturbed responses in glucose tolerance test in comparison with the loxp-negative Cre control mice (Scnn1awt/wt, Ins1-Cre+). Taken together, these results have suggested an important role of ENaC in regulating the excitability of β cells and insulin secretion, which may contribute to the understanding of Na+ environment in relation to insulin homeostasis. This work was supported in part by National Natural Science Foundation of China (82071599), Areas of Excellence Scheme of Hong Kong (AoE/M-402/20) and Bai Cheng Bai Yuan Start-up Fund (I2022A008). Presentation: Saturday, June 17, 2023