Figure 1: Scheme representing the general topology of Cx channels. Each connexin molecule [lower insert, bottom] has four transmembrane domains [M1-M4], two extracellular loops [E1 and E2], one cytoplasmic loop [CL] and both the N and C-terminus on the cytoplasmic side. Six Cx molecules form a hemichannel and docking of two hemichannels forms a gap junction channel. Thus, hemichannels connect the intracellular and the extracellular space, whereas gap-junction channels connect neighboring cells [cell 1 and cell 2].