Mammalian Cl^- channels can be broadly classified into four different families: voltage-dependent Cl^- channels (CLCs), the cystic fibrosis transmembrane conductance regulator (CFTR), ligand-gated Cl^- channels (g-aminobutyric acid (GABA)) and glycine channels) and Ca²⁺-activated Cl^- channels (Bestrophin and Anoctamin channels).

Bestrophins were first found by genetic linkage of human-Bestrophin-1 (hBest1) to a juvenile form of macular degeneration called Best vitelliform macular dystrophy (BVMD)^1,2. BVMD is mainly electrophysiologically characterized by a decrease in the light peak and physiologically by the thinning of the retina layer which eventually leads to the loss of central vision³. To date Bestrophin 1-4 have been identified, although Bestrophin-3 and Bestrophin-4 have been observed only at the RNA level³. In addition, splice variants of some of these Ca²⁺-activated Cl^- channels (CaCCs) have also been detected^2,4,5. CaCCs are known to be involved in the regulation of olfaction, taste, phototransduction, and excitability in the nervous system. Recently, Bestrophin-1 was shown to be functionally expressed in astrocytes in both primary cell culture and in situ⁶. Bestrophin-1 is also detected in retina, brain, spinal cord and testes⁷.

Two different topologies for Bestrophin-1 have been proposed. The first, the preferred structure, proposes that six hydrophobic domains span the membrane⁸, while the second suggests that there are only four membrane-spanning domains⁹. Bestrophin-1, along with its counterparts, is activated by intracellular Ca²⁺. A recent study demonstrated that Bestrophin-1 indeed binds Ca²⁺ and by mutating specific residues, showed which amino acid residues are essential for binding Ca^{2+ 10}, providing additional evidence that Bestrophin-1 is activated by direct binding of Ca²⁺ to the channel^11,12.