Pulsatile insulin secretion from individual beta cells is driven by oscillation of the calcium concentration in the cells. In beta cells lacking contact (i.e. outside islet of Lagerhans), the periodicity of these oscillations is rather variable (2-10 min). However, within an islet of Langerhans, the oscillations become synchronized by electrical coupling between closely located beta cells that are connected by gap junctions, and the periodicity is more uniform (3-6 min).  In addition to gap junctions, pulse coordination is managed by ATP signaling. α and δ cells in the pancreas also share secrete factors in a similar pulsatile manner.