Glucolipotoxic Conditions Affect Membrane Potential Wave Velocity Determined in Intact Islets Using Microelectrode Arrays

Pancreatic β-cells form highly connected networks within pancreatic islets. Each cell shows upon stimulation an oscillatory depolarization of the membrane potential and subsequent changes in [Ca2+]c. These signals propagate through the islet. The extent to which this coordinated islet cell activity is determined by a subset of β-cells is currently under discussion. In order to determine factors that influence this propagation, we have chosen a new method to identify wave propagation. We used high-resolution microelectrode arrays (CMOS-MEA) to measure voltage changes in the membrane potential of islet cells within the intact mouse islet. For network analysis, the individual electrode traces were compared with each other to gain insight into connectivity. The node degree of an islet (treated with 10 mM glucose) appears to be higher in the middle, but on average it was 8±2 degrees. Furthermore, algorithms were established to track the wave propagation from electrode to electrode, i.e. approximately from cell to cell. Treatment of isolated islets from C57BL6 mice with increasing glucose concentrations revealed that 15 mM glucose significantly reduced the wave duration compared to 6, 8 and 10 mM glucose (6 mM glucose: 10±4 s, n=32, vs. 15 mM glucose 7±2 s, n=26, p=0.0007). Additionally, the wave velocity was increased with rising glucose concentrations (6 mM glucose: 72±33 µm/s, n=20, vs. 8 mM glucose 118±69 µm/s, n=25, p=0.009). However, when the islets were pre-incubated with glucolipotoxic medium (25 mM glucose, 100 µM palmitate) for 72 h to mimic pre-diabetic conditions the wave velocity (waves induced by 8 mM glucose) was reduced (control: 87±40 µm/s, n=19, vs. GLT 64±32 µm/s, n=25, p=0.04). The results show that propagating waves of membrane depolarization are likely an important aspect for a functioning islet. The established technique proves to be suitable for tracking signal propagation and opens a wide field for further studies on islet network signaling. Disclosure A.K.Gresch: None. T.Deickert: None. J.D.Hüwel: None. J.Briggs: None. C.Beecks: None. R.K.Benninger: None. M.Düfer: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (R01DK102950R01, DK106412)