Overlapping expression of anion exchangers in the cochlea of a non-human primate suggests functional compensation

Ion homeostasis in the inner ear is essential for proper hearing. Anion exchangers are one of the transporters responsible for the maintenance of homeostasis, but their expression profile in the primate cochlea has not been fully characterized. However, species-specific overlapping expression patterns and functional compensation in other organs, such as the kidney, pancreas and small intestine, have been reported. Here, we determined the expression patterns of the anion exchangers SLC26A4, SLC26A5, SLC26A6, SLC26A7, SLC26A11, SLC4A2 and SLC4A3 in the cochlea of a non-human primate, the common marmoset (Callithrix jacchus). Although the pattern of expression of SLC26A4 and SLC26A5 was similar to that in rodents, SLC26A7, SLC4A2, SLC4A3 exhibited different distributions. Notably, five transporters, SLC26A4, SLC26A6, SLC26A11 SLC4A2 and SLC4A3, were expressed in the cells of the outer sulcus. Our results reveal a species-specific distribution pattern of anion exchangers in the cochlea, particularly in the outer sulcus cells, suggesting functional compensation among these exchangers. This "primate-specific" pattern may be related to the human-specific hearing loss phenotypes of channelopathy disorders, including the SLC26A4-related diseases Pendred syndrome/DFNB4.