Developmental Expression of Membrane Pumps and Ion Channels in Human Vestibular Endolymph Homeostasis

The expression patterns of key membrane pumps and ion channels involved in endolymph cycling have been studied in the rodent inner ear and the developing and adult human cochlea. However, little is known about their expression during the development of the human vestibular system. In this study, we provide a comprehensive overview of expression profiles of ion pumps, cotransporters, and exchangers in the developing human utricle and ampullae from fetal week (FW) 8 to 17. Immunohistochemistry analysis revealed that ATP1A1 and ATP1B2 co-localize at the basolateral membranes of dark cells. In addition, BSND expression was observed in transitional cells and dark cells in both the ampulla and utricle from FW10. We further characterized the expression of gap junction proteins (GJA1, GJB2, and GJB6) and found that KCNQ1 was expressed by transitional cells and dark cells starting from FW14. SLC12A2 immunostaining was detected in dark cells around FW10. Lastly, we investigated the spatiotemporal expression of pendrin. These detailed observations of protein expression during human inner ear development enhance our understanding of endolymph homeostasis.