Abstract
We evaluated the role of extracellular UTP and other nucleotides in the regulation of active ion transport across the pigmented rabbit conjunctiva. When added to the mucosal side of the conjunctiva, UTP (0.01–1000 μM), increased the short-circuit current by up to 14.6 ± 2.1 μA/cm2. The half-maximal concentration was 11.4 ± 2.3 μM. The serosal absence of Cl−, serosal presence of 10 μM bumetanide, and mucosal presence of 0.3 mMN-phenylanthranilic acid significantly reduced the change in the short-circuit current (ΔIsc) induced by 10 μM UTP by 78, 77, and 42%, respectively. Mucosal 10 μM UTP significantly increased 36Cl flux in the serosal-to-mucosal direction by 0.17 μEq/cm2/h, while not affecting mucosal-to-serosal36Cl flux. By contrast, 22Na transport in either direction was unaffected. The rank order of ΔIsc elicited by adenosine and nucleotides was consistent with the predominant involvement of P2Y purinergic receptors in the UTP effect on conjunctival ion transport. Moreover, the ΔIsc elicited by UTP was inhibited by 0.05 and 1 mM suramin (a P2-purinergic receptor antagonist), resulting in a rightward shift of the half-maximal concentration to 106.7 ± 1.3 μM. In conclusion, the primary effect of UTP on ion transport in the pigmented rabbit conjunctiva is stimulation of Cl− secretion, possibly at the P2Y2 and/or the P2Y4 receptor on the mucosal side of the tissue. Because of the coupling of fluid flow with Cl− secretion, UTP or its analogs may be considered for stimulating transconjunctival fluid flow in the dry-eye state.
Footnotes
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Send reprint requests to: Vincent H. L. Lee, Department of Pharmaceutical Sciences, University of Southern California, School of Pharmacy, 1985 Zonal Ave., PSC 704, Los Angeles, CA 90033. E-mail: vincentl{at}hsc.usc.edu
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↵1 This work was supported in part by National Institutes of Health Grants EY10421 (to V.H.L.L.), HL38658 (to K.-J.K.), and HL46943 (to K.-J.K.).
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↵2 Present address: Department of Molecular Biopharmacy and Genetics, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan.
- Abbreviations:
- PD
- potential difference
- ATPγS
- adenosine 5′-O-(3-thiotriphosphate)
- α,β-methylene ATP
- α,β-methyleneadenosine 5′-triphosphate
- BzATP
- 2′-3′-O-(4-benzoylbenzoyl)-adenosine 5′-triphosphate
- CF
- cystic fibrosis
- DMPX
- 3,7-dimethyl-1-propargylxanthine
- DPCPX
- 8-cyclopentyl-1,3-dipropylxanthine
- G protein
- guanine nucleotide-binding protein
- Isc
- short-circuit current
- ΔIsc
- change in short-circuit current
- Jms
- flux in the mucosal to serosal direction
- Jsm
- flux in the serosal to mucosal dorection
- Jnet
- net flux
- ΔJnet
- change in net flux
- ΔJIsc, eq
- net flux based on short-circuit current
- 2-MeSADP
- 2-(methylthio)-adenosine 5′-diphosphate
- 2-MeSATP
- 2-(methylthio)-adenosine 5′-triphosphate
- NPAA
- N-phenylanthranilic acid
- PPADS
- pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonic acid tetrasodium
- T1/2
- half-life
- TEER
- transepithelial electrical resistance
- Received March 23, 1999.
- Accepted May 25, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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