Many Cl- channels such as CFTR, ClC, CaCC, and ligand-gated anion channels are permeable to bicarbonate (HCO3-) which is an important anion in the regulation of pH. Many tissues, including retinal pigment epithelium (RPE), utilize HCO3- transporters to mediate transport of HCO3-. Bestrophns 1-4 (BEST1-4, aka vitelliform macular dystrophy proteins) have high permeability to HCO3- (Hu & Hartzell 2008). Defective BEST1 may play a role in macular degeneration in the eye due to impaired HCO3- and Cl- conductance (Hu & Hartzell 2008).