Fig. 1.

Schematic diagram of the evolutionary relationships among some key families in the ion channel superfamily. On the top of the figure is the structure of the channels moving from left to right showing a linear leak K⁺ channel that is composed of two membrane-spanning helices and a pore (blue), a 6TM channel with a single voltage sensor (red), and four domain 4x6TM channels with four voltage sensors. There is uncertainty about the origin of the 4x6TM family, which more likely evolved in eukaryotes than prokaryotes, as indicated in this figure. A more precise and detailed relationship among Cav and Nav channels in basal metazoans and their sister group, the choanoflagellates, is given in Fig. 3. Reprinted from Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 129/1, Peter A. V. Anderson, Robert M. Greenberg, Phylogeny of ion channels: Cues to structure and function, 12-17, Copyright (2001), with permission from Elsevier.