Figure 2: Different membrane proteins account for different modalities of β-cell communication. Connexins mediate the direct cell-to-cell transfer of cytosolic molecules (dotted, double arrow head) between adjacent cells, an event referred to as cell-to-cell coupling. Pannexins mediate the exchange of molecules (dotted) between the cytosol and the extracellular space of cells. Some of the cytosolic molecules which exit cells through pannexin channels could ensure paracrine communication between close-by cells. Occludin and claudins provide for the sealing of small domains of the cell membrane and of portions of the islet extracellular spaces, hence establishing the polarity of β-cells. Cadherins and N-CAM ensure the adhesion between islet cells in contact. Integrins mediate the adherence of islet cells to the extracellular basal lamina (grey band) and matrix. Claudins, cadherins, N-CAM, and integrins also provide for the in-out and out-in signaling of β-cells (curved, double arrow heads) notably with regard to gene expression.