Channel-forming tight junction protein with selectivity for anions, including chloride and hydrogencarbonate, and for solutes smaller than 9 Angstrom in diameter. In the kidney proximal tubule, may be involved in paracellular reabsorption of filtered anions. Does not affect water permeability. {ECO:0000269|PubMed:22402829, ECO:0000269|PubMed:26194246}. This is the function of CLDN17 (claudin 17, Ensembl gene identifier ENSG00000156282).