Excitation wave propagation as a possible mechanism for signal transmission in pancreatic islets of Langerhans

In response to glucose application, beta -cells forming pancreatic islets o f Langerhans start bursting oscillations of the membrane potential and intr acellular calcium concentration, inducing insulin secretion by the cells, U ntil recently, it has been assumed that the bursting activity of beta -cell s in a single islet of Langerhans is synchronized across the whole islet du e to coupling between the cells. However, time delays of several seconds in the activity of distant cells are usually observed in the islets of Langer hans, indicating that electrical/calcium wave propagation through the islet s can occur. This work presents both experimental and theoretical evidence for wave propagation in the islets of Langerhans. Experiments with Fura-2 f luorescence monitoring of spatiotemporal calcium dynamics in the islets hav e clearly shown such wave propagation. Furthermore, numerical simulations o f the model describing a cluster of electrically coupled beta -cells have s upported our view that the experimentally observed calcium waves are due to electric pulses propagating through the cluster. This point of view is als o supported by independent experimental results. Based on the model equatio ns, an approximate analytical expression for the wave velocity is introduce d, indicating which parameters can alter the velocity. We point to the poss ible role of the observed waves as signals controlling the insulin secretio n inside the islets of Langerhans, in particular, in the regions that canno t be reached by any external stimuli such as high glucose concentration out side the islets.