195-OR: To Which Degree Do Alpha Cells Shape the Role of the Beta Cells First Responders?

Abstract

Calcium (Ca2+) uptake drives glucose-stimulated insulin secretion from the pancreatic β-cells. The “1st responder” subpopulation of β-cells disproportionally control the Ca2+ uptake during the first phase, which is disrupted with ageing and in diabetes. Here we determine whether alpha and delta cells play a formative role in the 1st responder β-cells state. We used MIP-CreER GCaMP6s mouse model which expresses Ca2+-sensitive GFP specifically in β-cells. We performed simultaneous recording of Ca2+ dynamics and gap junction permeability in individual islets. We stimulated islets with glucose, and with the GLP1-R antagonist, exendin 9-39 (Ex9). Based on the first-phase Ca2+ dynamics we defined the “1st responder” and the “last responder” cells. We tested their consistency under repeated glucose stimulation with and without the Ex9. We next stained them for insulin, glucagon, and somatostatin and measured distances in 3D from all β-cells to alpha and delta cells. The Ex9 disrupted the 1st responder consistency (only half of the original 1st responders remained such under repeated glucose stimulation), compared to the control experiment. Ex9 increased the islet's first-to-last cell response time by 150 +/- 74 seconds making islet's response to glucose two times more heterogeneous compared to control (p=0.0517). On average 1st responders were located closer to the alpha cells, and last responders - further from them (p=0.0039). At the same time, first responders had significantly less delta cell neighbors compared to the last responders (p=0.0137). Our gap junction permeability data showed no gap junction activity in alpha-beta cell couples. In conclusion, 1st responder beta cells have more alpha cell and less delta cell neighbors than last responders. The role of the alpha cell in the formation of the 1st responder cell state is likely realized via paracrine interaction. Disclosure V.Kravets: None. C.H.Levitt: None. R.K.Benninger: None. Funding Burroughs Wellcome Fund (25B1756 to V.K.); National Institutes of Health (R01DK102950, R01DK106412 to R.K.B.); Human Islet Research Network (UC24DK104162 to V.K.)