Molecular basis of ocular abnormalities associated with proximal renal tubular acidosis
Tomohiko Usui, … , Makoto Araie, George Seki
Tomohiko Usui, … , Makoto Araie, George Seki
Published July 1, 2001
Citation Information: J Clin Invest. 2001;108(1):107-115. https://doi.org/10.1172/JCI11869.
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Article

Molecular basis of ocular abnormalities associated with proximal renal tubular acidosis

Abstract

Proximal renal tubular acidosis associated with ocular abnormalities such as band keratopathy, glaucoma, and cataracts is caused by mutations in the Na+-HCO3– cotransporter (NBC-1). However, the mechanism by which NBC-1 inactivation leads to such ocular abnormalities remains to be elucidated. By immunological analysis of human and rat eyes, we demonstrate that both kidney type (kNBC-1) and pancreatic type (pNBC-1) transporters are present in the corneal endothelium, trabecular meshwork, ciliary epithelium, and lens epithelium. In the human lens epithelial (HLE) cells, RT-PCR detected mRNAs of both kNBC-1 and pNBC-1. Although a Na+-HCO3– cotransport activity has not been detected in mammalian lens epithelia, cell pH (pHi) measurements revealed the presence of Cl–-independent, electrogenic Na+-HCO3– cotransport activity in HLE cells. In addition, up to 80% of amiloride-insensitive pHi recovery from acid load in the presence of HCO3–/CO2 was inhibited by adenovirus-mediated transfer of a specific hammerhead ribozyme against NBC-1, consistent with a major role of NBC-1 in overall HCO3– transport by the lens epithelium. These results indicate that the normal transport activity of NBC-1 is indispensable not only for the maintenance of corneal and lenticular transparency but also for the regulation of aqueous humor outflow.

Authors

Tomohiko Usui, Masumi Hara, Hiroaki Satoh, Nobuo Moriyama, Humie Kagaya, Shiro Amano, Tetsuro Oshika, Yasuo Ishii, Nobuhiro Ibaraki, Chiaki Hara, Motoei Kunimi, Eisei Noiri, Kazuhisa Tsukamoto, Jun Inatomi, Hayato Kawakami, Hitoshi Endou, Takashi Igarashi, Astuo Goto, Toshiro Fujita, Makoto Araie, George Seki

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Figure 8

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Possible roles of NBC-1 in the ocular tissues. Large arrows indicate the...
Possible roles of NBC-1 in the ocular tissues. Large arrows indicate the direction of net fluid transport. In the cornea (a) and lens (b), NBC-1 likely contributes to the net fluid transport. In the trabecular meshwork cells (c), NBC-1 may affect the contractility of these cells via interaction with L-type Ca2+ channels. In the ciliary epithelium (d), the contribution of NBC-1 to the net fluid transport remains to be established.