Ligand-gated anion channel that allows the movement of anions across cell membranes when activated by calcium (Ca2+) (PubMed:11904445, PubMed:18400985, PubMed:32251414, PubMed:35789156, PubMed:36289327). Transports a large specter of anions, namely mediates the movement of chloride, L-glutamate and iodide (PubMed:11904445, PubMed:18400985, PubMed:32251414, PubMed:35789156, PubMed:36289327). Calcium-binding triggers the dilation of the aperture, but calcium- dependent gating is only effective when the size of the passing anion is bigger than the closed aperture (By similarity). Mediates the calcium-activated hydrogencarbonate movement and participates in colonic hydrogencarbonate secretion concomitant with mucin secretion (By similarity). In non-pigmented epithelium (NPE), mediates the efflux of intracellular L-glutamate; binding of intracellular L-glutamate activates and open both the neck and the aperture of the channel, leading to L-glutamate exit promoting chloride influx movement from the extracellular side in trans (PubMed:36289327). Also exhibits a directional permeability for intracellular glutamine, in a similar manner as for L-glutamate (PubMed:36289327). {ECO:0000250|UniProtKB:E1BF86, ECO:0000250|UniProtKB:Q8BGM5, ECO:0000269|PubMed:11904445, ECO:0000269|PubMed:18400985, ECO:0000269|PubMed:32251414, ECO:0000269|PubMed:35789156, ECO:0000269|PubMed:36289327}. This is the function of BEST2 (bestrophin 2, ENSG00000039987).