Abstract
In this study, the transport mechanism of NG-nitro-l-arginine (L-NA), a nitric oxide synthase inhibitor that may be useful for alleviating intraocular inflammation, was characterized in the pigmented rabbit conjunctiva. L-NA, when applied to the mucosal side of the conjunctiva, led to dose-dependent increases in the short-circuit current (Isc) at 37°C but not at 4°C or under the Na+-free condition. Serosally added 1 mM L-NA did not elicit any change in the Isc. Mucosally added 1 mM L-NA elicited a net absorptive Na+ flux of 0.09 μEq/(cm2·hr), comparable with the Isc change. L-NA transport at 0.1 mM in the mucosal-to-serosal (ms) direction was 22 times greater than that in the serosal-to-mucosal direction. There was a good correlation between the ms flux of L-NA and the Isc changes elicited by L-NA under the same experimental conditions. L-NA transport was saturable, with aKm of 0.35 mM and a maximal flux of 290 pmol/(cm2·min). Hill analysis of L-NA flux observed at 0.1 mM L-NA in response to varying Na+concentrations in the mucosal bathing fluid yielded a Hill coefficient of 0.98, suggesting a 1:1 coupling between Na+ and L-NA. Moreover, ms 3H-L-NA transport was inhibited by basic amino acids (L-Arg and L-Lys) and a neutral amino acid (L-Leu), but not by an acidic amino acid (L-Glu) and the d-stereoisomer of L-NA. In the case of L-Arg, inhibition was competitive with aKi of 0.034 mM. Taken together, the above findings are consistent with the involvement of the L-Arg transport system B0,+ in the conjunctival transport of L-NA.
Footnotes
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Send reprint requests to: Vincent H. L. Lee, Ph.D., Department of Pharmaceutical Sciences, University of Southern California, School of Pharmacy, 1985 Zonal Avenue, 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 (V.H.L.L.) and HL38658 (K.-J.K.).
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↵2 Present address: Department of Pharmaceutics, Faculty of Pharmaceutical Sciences, Tohoku University, Aoba, Aramakiaza, Aoba-ku, Sendai 980–8578, Japan.
- Abbreviations:
- L-NA
- NG-nitro-l-arginine
- ms
- mucosal-to-serosal
- sm
- serosal-to-mucosal
- Papp
- apparent permeability coefficient
- L-Arg
- l-arginine
- L-Lys
- l-lysine
- L-Leu
- l-leucine
- L-Glu
- l-glutamic acid
- NO
- nitric oxide
- NOS
- nitric oxide synthase, iNOS, inducible nitric oxide synthase
- L-MMA
- NG-monomethyl-l-arginine
- L-NAME
- NG-nitro-l-arginine methyl ester
- D-NA
- NG-nitro-d-arginine
- PD
- potential difference
- Isc
- short-circuit current
- ΔIsc
- increase in short-circuit current
- TEER
- transepithelial electrical resistance
- JNams
- Na+ flux in the ms direction
- JNasm
- Na+ flux in the sm direction
- JNanet
- net Na+flux
- Received July 21, 1997.
- Accepted December 3, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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