蝸牛外側壁におけるGastric H<SUP>+</SUP>,K<SUP>+</SUP>-ATPase の発現と蝸牛内リンパ電位への役割

Cochlear endolymph has a highly positive potential of ∼+80 mV. This so-called endocochlear potential (EP) is essential for hearing and maintained by K⁺-circulation from perilymph to endolymph through cochlear lateral wall. Gastric H⁺,K⁺-ATPase is reported to occur in stria vascularis and spiral ligament of the lateral wall. However, its precise distribution and physiological roles are still unknown. In this study, we therefore examined the localization and function of the H⁺,K⁺-ATPase in mammalian cochlea. RT-PCR analysis identified that gastric α1 but not colonic α2 subunit of H⁺,K⁺-ATPase dominates in cochlea. The immunolabeling using an antibody specific for the α1 subunit revealed that the H⁺,K⁺-ATPase is strongly expressed in intermediate cells of stria vascularis, the tissue which plays a central role in formation of EP. The clear immunoreactivity was also detected in types II, IV, and V fibrocytes of spiral ligament and those of spiral limbus, all of which are involved in cochlear K⁺-circulation. Finally, vascular perfusion of a specific blocker for gastric H⁺,K⁺-ATPase, SCH28080, dramatically reduced EP. These results strongly suggest that gastric H⁺,K⁺-ATPase in cochlear lateral wall positively regulates the K⁺ circulation and is crucial for generation of positive EP. [Jpn J Physiol 55 Suppl:S162 (2005)]