Regional differences in rat conjunctival ion transport activities

Active ion transport and coupled osmotic water flow are essential to maintain ocular surface health. We investigated regional differences in the ion transport activities of the rat conjunctivas and compared these activities with those of cornea and lacrimal gland. The epithelial sodium channel (ENaC...

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Bibliographic Details
Published in:American Journal of Physiology: Cell Physiology 2012-10, Vol.303 (7), p.C767-C780
Main Authors: Yu, Dongfang, Thelin, William R, Rogers, Troy D, Stutts, M Jackson, Randell, Scott H, Grubb, Barbara R, Boucher, Richard C
Format: Article
Language:English
Subjects:
Animals
Cell culture
Cells, Cultured
Conjunctiva - metabolism
Female
Gene expression
Humans
Ion Channels - metabolism
Ion Transport - physiology
Ions
Male
Organ Culture Techniques
Proteins
Rats
Rats, Sprague-Dawley
Rodents
Tissues
Xenopus laevis
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Summary:Active ion transport and coupled osmotic water flow are essential to maintain ocular surface health. We investigated regional differences in the ion transport activities of the rat conjunctivas and compared these activities with those of cornea and lacrimal gland. The epithelial sodium channel (ENaC), sodium/glucose cotransporter 1 (Slc5a1), transmembrane protein 16 (Tmem16a, b, f, and g), cystic fibrosis transmembrane conductance regulator (Cftr), and mucin (Muc4, 5ac, and 5b) mRNA expression was characterized by RT-PCR. ENaC proteins were measured by Western blot. Prespecified regions (palpebral, fornical, and bulbar) of freshly isolated conjunctival tissues and cell cultures were studied electrophysiologically with Ussing chambers. The transepithelial electrical potential difference (PD) of the ocular surface was also measured in vivo. The effect of amiloride and UTP on the tear volume was evaluated in lacrimal gland excised rats. All selected genes were detected but with different expression patterns. We detected αENaC protein in all tissues, βENaC in palpebral and fornical conjunctiva, and γENaC in all tissues except lacrimal glands. Electrophysiological studies of conjunctival tissues and cell cultures identified functional ENaC, SLC5A1, CFTR, and TMEM16. Fornical conjunctiva exhibited the most active ion transport under basal conditions amongst conjunctival regions. PD measurements confirmed functional ENaC-mediated Na(+) transport on the ocular surface. Amiloride and UTP increased tear volume in lacrimal gland excised rats. This study demonstrated that the different regions of the conjunctiva exhibited a spectrum of ion transport activities. Understanding the specific functions of distinct regions of the conjunctiva may foster a better understanding of the physiology maintaining hydration of the ocular surface.
ISSN:0363-6143
1522-1563
1522-1563
DOI:10.1152/ajpcell.00195.2012