319-OR: First Responder Beta-Cell Subpopulation Affects Islet Response to Glucose

Glucose-stimulated insulin secretion from the pancreatic β-cells is driven by calcium (Ca²⁺) uptake. In mice Ca²⁺ is disproportionally controlled by functional subpopulations of β-cells, identified in affecting 2^nd phase oscillatory Ca²⁺ response. Yet, the “1^st-responder” cells that lead the 1^st Ca²⁺phase disrupted in early diabetes were overlooked. It is unknown whether 1^st responders are a distinct subpopulation, and if so, which factors underlie this distinction, and what is their role. We hypothesized that 1^st responder metabolic and electrical parameters are distinct from the known β-cell subpopulations, and they play an important role in the 1^st Ca²⁺phase of the islet response. We simultaneously measured Ca²⁺ dynamics and electrical coupling in intact islets using β-cells specific expression of the Ca²⁺ sensor GCaMP6s. We performed repeated glucose and Kapt channel blocker stimulation of the islet. We used femtosecond laser ablation of specific cells. This was complimented by multicellular islet electrophysiology model where we could remove specific cells from the islet and evaluate glucokinase rate, Katp and coupling conductance of the cells. We found no overlap of 1^st responder with either “wave-initiator”, leading Ca²⁺ wave, or highly connected “hub” cell subpopulations, based on the oscillatory 2^nd phase Ca²⁺ wave coordination. Interestingly 1^st responders were less electrically coupled (p=0.0157), supported by simulations. 1^st responders were consistent under repeatable glucose stimulation and remained 1^st responders under the Katp channel blocker, supported by computational results of lower than average Katp channel conductance (p<0.0001). Removing 1^st responder from the islet resulted in delayed 1^st phase islet response compared to the random cell removal, both in experiment and simulation (p=.0428).

In conclusion, 1^st responders are distinct β-cell sub-population, which influences the islet 1^st phase Ca²⁺response.